woldson Posted December 23, 2009 Share Posted December 23, 2009 Sticky in the misc. section. Fantastic read! Synopsis: Chapter one - motor oil 101 The way motor oil is labeled is inherently misleading. Most people think a 0W-30 is too thin for an engine that recommends 10W-30. This is wrong. People think in terms of the oil thinning when it gets hot, they think this thinning with heat is the problem with motor oil. It is more correct to think that oil thickens when it cools and THIS is the problem. Oils are chosem by the mfr to give the right thickness at the normal operating temperature of the engine. Average everyday oil temp is 212F and on the track up to 302F. These two different operating temperatures require different oils. We are dealing with a system of numbers that does not relate to the viscosity inside the can but at operating temp. The viscosity varies with temperature as well. A 30 weight oil has a viscosity of 3 at 302F and thickens to 10 at 212F. It further thickens to 100 at 104F and is too thick to measure at 32F. Engine designers usually call for their engines to run at 212F oil and water temperature with oil thickness of 10. This is the viscosity/thickness of the oil not the weight as labeled. If the thickness of your oil when you got in your car this morning was 10 and after your commute was nearly done was 10, we'd live in perfectland. There would be little to no engine wear and tear. When you drove home from work that evening the car reached the correct operating temperature and the oil was a thickness of 10 - ideal. Overnight, the engine cooled to ambient temperature and the oil thickened. It's is now 75F and the oil thickness is around 150. It is too thick to lubricate an engine designed to run with an oil having a thickness of 10. Now the concept of lubrication. Most believe pressure = lubrication, this is WRONG. Flow = lubrication. If pressure = lubrication then we would all use the heaviest oil possible. Lubrication is used to separate moving parts, to keep them from touching. There is a 1:1 relationship between flow and separation. Pressure and flow are in opposition. If you change your oil to a thicker formula the pressure will go up - there is more resistance to flow and flow must go down in order for pressure to go up. There is an inverse relationship. Thinner oil will cause pressure to go down, this occurs and flow is increased. Example - Ferrari 575 Maranello driven around town. The manual states the target pressure is 75psi at 6,000RPM. The gold standard is that all engines should have a pressure of 10psi for every 1,000RPM. (10:1) You do need some pressure to move oil along, but only enough pressure, not more. More pressure is not better, it only results from the impedance of oil flow. 2.3L Oil Pressure Target per factory manual: 57-94 PSI @ 3,000 RPM Ferrari is not saying what thickness of oil to use. That can only be determined by experimentation. In this situation oil temp is sitting around 185F around town on a hot Florida day. The thinnest API/SAE certified oil is Mobil 1's thinnest, even so the result is 80psi @ 2,000RPM. Is it too thick for the application (low temp low RPM) yet the thinnest oil money can buy. If on a hot Florida track mid-summer the oil temperature would probably get to 302F and the pressure would be about 40psi @ 6,000RPM - the oil is too thin for this application (high temp high RPM). High flow does more than lubricate, it cools the hottest frictional parts of an engine. Example and older 550 Maranello. It only specified 5W-40 Shell Helix Ultra as the oil to use in all conditions. This car was designed for racing. As it turns out Ferrari now recognizes that not every owner races their cars. The newer 575 now states 0W-40 for around town situations, 5W-40 for racing, and 10w-60 for hot climate racing. They now realize the difference between the daily urban driver and the very different racing situation. Now when manuals call for 10W-30 a 0W-30 is always the better choice, ALWAYS. The 0W-30 is not thinner, it is the same thickness at operating temp as the 10W-30. The difference between them is when cold. As cooling occurs, the oils have gotten thicker, too thick to adequately lubricate the engine. The 10W thickened to a 90 and the 0W to about a 40. Both are too thick (more than the engine's desired 10) to do the job at this temperature. You are better starting off with a viscosity of 40 than 90. People think in terms of the oil thinning when it gets hot, people SHOULD think that it thickens when it gets cold. Chapter Two - motor oil 102 0W-30 and 10W-30 oils have the same thickness at operating temperature. The 0W-30 does not thicken as much when cooling occurs as opposed to the 10W-30. Oil type.........Thickness at 75 F Thickness at 212 F 30 Weight......250......................10 10W-30.........100......................10 0W-30...........40.......................10 10 Weight......30........................6 The difference between the desired thickness your engine requires ( = 10 ) is closest to the 0W-30 oil at startup. It is still too thick for normal operation. But it does not have far to go before it warms up and thins to the correct viscosity. Remember that most engine wear occurs at startup when the oil is too thick to lubricate properly. It cannot flow and therefore cannot lubricate. Most of the thick oil at startup actually goes through the bypass valve back to the engine oil sump and not into your engine oil ways. This is especially true when you really step on that gas pedal. You really need more lubrication and you actually get less. Note that a straight 10 weight oil is also too thick for your engine at startup - thickness of 30. At operating temperatures it is too thin having a thickness of 6. It needs to be around 10. The oil companies have added viscosity index improvers or VI to oils to solve this dilemma. They take a mineral based oil and add VI improvers so that it does not thin as as much when it gets hotter. Now instead of only having a thickness of 6 when hot it has a thickness of 10, just as we need. The penalty is the startup thickness also goes up to 100. It's better than being up at 250 as a straight 30 weight oil though. Oil with a startup thickness of 100 that becomes the appropriate thickness of 10 when fully warmed up is called a 10W-30 weight motor oil. This is NOT as thick as a straight 30 weight oil at startup and it is NOT as thin as a straight 10 weight oil at full operating temperature. The downside of a mineral based multigrade oil is that this VI additive wears out over time and you end up with the original straight 10 weight oil. It will go back to being too thin when hot. It will have a thickness of 6 instead of 10 at operating temperature. This may be why Porsche does not want a 0W-30 but rather a 10W-30. If the VI wears out the mineral 0W-30 will ultimately be thinner, a straight 0 weight oil. When the VI is used up in the 10W-30 oil it too is thinner. It goes back to a straight 10 weight oil. They are both still too thick at startup, both of them. The straight 0 weight oil, a 5 weight oil, and a 10 weight oil are all too thick at startup. With normal oil change intervals the VI improver will not wear out and so the problem does not really exist. In fact, oils do thin a little with use. What is more interesting is that with further use motor oils actually thicken and this is much worse than the minimal thinning that may have occurred earlier. Synthetic oils are a whole different story. There is no VI improver added so there is nothing to wear out. The actual oil molecules never wear out. You could almost use the same oil forever. The problem is that there are other additives and they do get used up. I suppose if there was a good way to keep oil clean you could just add a can of additives every 6 months and just change the filter, never changing the oil. When the additives wear out in a synthetic oil it still has the same viscosity. These oils will always have the correct thickness when hot and will still be too thick at startup as with all oils of all types, regardless of the API / SAE viscosity rating. Automotive engine manufacturers know there is thinning or thickening that will occur. They take these things into account when they write that owners manual. The reality is that motor oils limit is both time itself (with no motor use) and/or mileage use. Chapter 3 - Thinking Synthetic? Good! Discussed before was how mineral oils are too thick at startup yet too thin when hot. The viscosity was corrected with the hot engine by adding VI improvers. A 10W-30 multigrade mineral based oil is made from a 10 weight oil and has VI improvers added to thicken the product in a 212 F engine. It acts as a 30 weight oil when hot. It acts more as a 10 weight oil at startup. A 10 or 5 or 2 weight oil is still too thick to provide lubrication at startup. Again, we are discussing the needs of my single hypothetical engine for around town driving. Oil type............Thickness at 75 F .........Thickness at 212 F Straight 30.......250...................................10 10W-30............100................................. ..10 0W-30................40.............................. ......10 Straight 10.........30..................................... 6 Straight 5...........20.................................... .4 Straight 2...........15.................................... .3 Straight 0...........12.................................... 3 est. A 10W-30 synthetic oil is based on a 30 weight oil unlike the counterpart. There is no VI improver needed. Synthetic oil is already correct for the normal operating temperature of 212 F. It will never thin yet has the same long term problem as the mineral based oil. They both thicken with extended age. There are some properties of synthetic oils that actually result is less wear than with mineral oils. Due to a reduction of internal friction of the synthetic oil your engine will run a bit cooler. Wear increases as temperature increases, all other things being constant. A main advantage that the synthetic has over the mineral based oil is the ability to lubricate at startup. Both types of oil have the same specifications at 104 F, 212 F and 302 F. It is the startup viscosity characteristics that separate these oils. Synthetic oils do not thicken as much on cooling. At temperatures below zero you will not be able to start your car with mineral oils while the synthetic oils may be used to -40 or - 50 F. Motor oil becomes permanently thicker with exposure to northerly winter type weather. This is more of a problem to mineral based oils. Waxes form. This is why it is a bad idea to even store a bottle of oil in a cold garage. It goes bad on the garage self just because it is exposed to the cold. ***** A Synthetic 10W-30 weight oil is based on a heavier 30 weight oil while the mineral based 10W-30 oil is based on a thinner 10 weight oil. They are both similar at operating temperatures yet the 30 weight based synthetic is actually less thick at startup and much less honey-like at low temperatures. This is the opposite of what common sense dictates. ***** Chapter 4 - Goes Nuts Mineral oil: .........................Thickness at 75 F.........212 F.........302 F Straight 30......250..................................10... ..............3 10W-30...........100.................................. .10................3 0W-30.............There are none Synthetic oil: .............................Thickness at 75 F.........212 F........302 F Straight 30...........100.................................1 0...............3 10W-30.................75............................. ......10...............3 0W-30...................40........................... ........10...............3 People sometimes use a thicker oil to minimize gasket leaks. Repair the gasket. Do not destroy your engine with an oil that is too thick for proper function. Some people have said they use thicker oils because they only use their cars every 2, 3 or 4 weeks and are afraid that thin oils will fall off the engine parts and result in a lack of lubrication at startup. Your lawn mower over the winter gets gummed up solid. The oil and fuel thicken over time resulting in engine failure. Oil on the surface of parts does not lubricate. It is the FLOW of oil between parts that lubricates. Thick, old, waxy oil can only be bad. Several car owner manuals are now stating that oils do not need to be changed but every 7,500 miles or more. The same manual also states OR every 12 months, whichever occurs first. My feeling is that you can probably go 5,000 miles on the average (in a sports car) but you must change your oil in the spring time at a minimum, particularly up north. Oils form waxes in icy cold weather causing a permanent thickening of the oil. Some automotive manufacturers are backing down on oil change intervals to 5,000 miles or less and some advocate changing the oil at least every 6 months as well. I think this is because of the tendency for oils to thicken in very hot engines (not ambient conditions, just hot engines). Also because of thickening from the cold of winter and from sludge build up that cannot be filtered out. I believe oil is much better being too thin than too thick. We have been going to thinner and thinner oils despite hotter engines with turbos and the like. Most people figure they need a 40 weight oils but then use a 50 instead. Better thinking is that if you think you need a 40, use a 30 weight oil instead. Synthetic oils do cling to parts better as they have higher film strength than mineral oils, are thinner overall, have greater slipperiness, and stick better to engine parts. Thickness of moving oil is measured in centiStokes or cS. Most engines want the oil viscosity to be around 10 cS at normal operating temperature. The really thick multigrade oils have a viscosity of 20 cS at operating temperature. One is not twice as thick as the other, it is only 10 cS thicker. As we increase the heat from 212 F to 302 F the most commonly recommended oil thins from 10 cS to 3 cS. The thicker oil drops from 20 cS to 4 cS. Note that in a very hot engine the difference between the two oils is now only 1-2 cS. They have about the same thickness. There is a lot of competition to get us the best working motor oil. Independent additives cannot make the oil better and in many cases makes things worse. There have been engine failures as a result of adding some of these aftermarket additives to motor oil. Motor oil that is labeled for RACING ONLY is not usable for every day driving. Often these have more additives that are toxic to your catalytic converters and the environment and generally do not have detergents. These are very important unless you plan on taking it apart every few weeks and cleaning every single surface. The oils do not meet the API / SAE requirements for ratings as SJ, SL, or now SM. You do not need to use the exact oil type and brand that your car manual tells you to use. Oils are pretty general. They are not that different. Ferrari is married to Shell. If you call them up and ask to use Valvoline instead they will tell you that they have not tested that brand in their cars. They only tested the engine with Shell oils. They cannot comment on the performance of other oils in their engines. This is a fair statement (legally). The reality is that the Shell and Valvoline oils of the same specification (viscosity, API and SAE ratings, synthetic or not) are very similar. People often say that their old 1980 car manual says to use a specific Brand-X motor oil. Just about any oil brand that meets the original specifications will do. All oils are much, much better now. The only downside of synthetic lubricants is the cost. They cost 2 or 3 times as much as mineral based oils. Chapter 5 - Racing vs Traffic Your oil will get up to 302 F, but your cooling system is around 212 F. The engine produces tremendous heat but can only pass it off so fast to the cooling system. There is a lot of air moving past the cooling radiator so the antifreeze / coolant is able to get rid of the extra heat from this part of the system with relative ease. The temperature of oil on your gauge is not as hot as it really gets. This temperature is an average, the oil gets as hot as 400 or 500 F in these racing situations in certain areas of your engine. Thicker oils are not necessarily needed in racing situations and a major function of oil is to cool the inside of your engine. Since the oil with a viscosity of 10 cS at 212 F thins to a viscosity of 3 cS at 302 F we will get more flow. This increased flow will result in increased cooling by the oil. This is a good thing. You would probably want more oil flow in these situations and you get it. The hotter oil thins and this increases flow. The higher flow works harder to separate the engine parts that are under very high stress. It all works out for the better. You do not necessarily need to go to a thicker oil while racing. Only experimentation will tell. The best way to figure out what viscosity of oil you need is to drive the car in the conditions you will use. Then use the oil viscosity that gives you 10 PSI per 1,000 RPM under those circumstances. For some reason very few people are able to get this simple principal correct. I cannot explain further. I am using 0W-20 in my Ferrari 575 Maranello right now. It has over 5,000 miles on the clock. There will be a day (my estimate is 50,000 miles) when I will have to go to a 0W-30. In the future I will have to increase the viscosity to a 0W-40, then a 0W-50, maybe. I will use whatever it takes to give me 75 PSI at 6,000 RPM during the lifetime of my engine. This formula works in all situations. Some people get a somewhat low oil pressure while at idle. This is fine. There is no stress on parts at idle, the smallest oil flow will do the trick. It is at higher RPM where more BHP is produced. This is where we need the flow. Ferrari uses 75 PSI at 6,000 RPM as the place to test your oil viscosity needs. If your oil gives this value under your driving conditions then your lubrication system has been maximized. Period. Do not go 5,000 miles with the same oil if you are racing your car. You should change the oil every 1 or 2,000 miles. Use racing oil on the track and urban oil around town. FYI. The Formula 1 cars that run at 15,000 RPM and higher use straight 5 and 10 weight oils. Now let me discuss what people *think* is a similar situation to racing. That is hot summer traffic jam driving. Your car should be able to handle this. When you drive that car down the road mid-winter in upstate New York or mid-summer in Florida the engine and oil temperatures will be around 212 F. But your Florida vacation is suddenly altered by a hurricane. You have to get out of Tampa, but so do a million other people. It is now 95 F and you are in a snarl. Everyone thinks they need a thicker oil for this situation. This is false. Your engine is not producing much heat at low RPM and low BHP output. Heat can easily be transmitted to your cooling system. The problem is that your cooling system has trouble getting rid of the heat. The oil and the coolant will slowly rise in temperature. They both rise together. The increase is no big deal for your oil. It goes to 220, then 230 F. The problem is that the cooling system can only handle heat up to 230 F. After that you overheat the cooling system and the car must be shut off. Do not change to a thicker oil based on your traffic situation. Chapter 6 left out as it is personal opinion and 2 years old on specific products Chapter 7 - Terminology from SAE and API Many think that the “W” in 10W-30 means “winter”. From SAE J300 p.2: "Two series of viscosity grades are defined in Table (1): (a) those containing the letter W and ( those without. Single viscosity grade oils with the letter W are defined by maximum low temperature cranking and pumping viscosities and a minimum kinematic viscosity at 100C. Single grade oils without the letter W are based on a set of minimum and maximum kinematic viscosities at 100C and a minimum high shear rate viscosity at 150C. The shear rate will depend on the test method. Multigrade grade oils are defined by both of these criteria.... The W is just a designation of one type of testing vs another. What is the viscosity of the various weight oils? The definitions are as follows: From SAE J300, viscosities at 212 F 20.........5.6 to 9.2 30.........9.3 - 12.4 40.........12.5 - 16.2 50.........16.3 - 21.8 60.........21.9 - 26.1 By a modified analysis the min. viscosity at 302 F 20..........2.6 30..........2.9 40..........2.9 - 3.7 50..........3.7 60..........3.7 The difference between the 20W and 60 weight oils at 302 F is only about 1 (one) whereas the difference in viscosity at 104 F is 120 units. The American Petroleum Institute, API, and Society of Automotive Engineers, SAE, have rated engine oil performance over the years. There are over 3 dozen tests that oil now must pass in order to make the next higher rating. Some tests have progressed to a zero tolerance level. For example there can be no sticking of any piston rings any more. SJ........SL 30........20......maximum cam plus lifter wear 9..........7.8.....sludge build up 5..........8.9.....varnish rating (more is better) 60.........45.......high temperature deposits 17.........10.......high temperature volatility Other categories include: Resistance to rust, resistance to foaming, resistance to oil consumption, homogeneity and miscibility, flow reduction with varying amounts of absorbed moisture, gelation index and others. From the previous SJ to the current SL rating is a significant improvement. Please note that it makes no difference what oil you are using. The 0W-20 Mobil 1 that is SL rated meets the same criteria as that SL rated 10W-30 synthetic or mineral based Pennzoil. That SJ or in particular that SH oil some people are looking for (from their older automotive owners manual) is no where near as good as any SL oil of today. Always use the most currently available, highest rated motor oil, even in the oldest, most worn engine. You may require a thicker grade in that worn engine but just make sure it is SL rated. (Editor's note: SM is now standard and readily available so use it!) See: American Society for Testing and Materials- www.astm.org Society of Automotive Engineers- www.sae.org American Petroleum Institute- www.api.org Chapter 8 - Stories & Examples One of the members of the Ferrari Chat web site went from a 40 to a 30 weight oil in his Ferrari 355 for racing in Texas. He noticed a drop in temperature but no change in oil pressure. This may seem odd but really makes perfect sense. Since the 30 weight oil is thinner he got better flow and therefore better cooling. The oil was at a lower temperature so it was not as thin than it would have been at the previous higher temperature. Cooler engines last longer. Fact: The higher the temperature, the greater the wear, all other things being equal. All manufacturers I have seen are specifying 0W-XX or 5W-XX oils now. Honda, Ferrari, Ford, Mercedes, Porsche, and others specify a 0 or 5W-XX oil to mention a few. These are appropriate for all engines of all ages of all levels of wear. This second number is the only thing that may change with an older, lose or worn engine. This can only be determined by experimentation. If you are using XW-50, go to a 0W-40. If your pressures are still too high go to a 0W-30 and so on. Most people who buy high powered cars that I have experienced will just get in there cars and step on the gas fully. They do not wait for the oil to warm up. Personally I would not mind running full BHP for short bursts during the break in period but I always fully warm up the engine first. Older engines may in fact benefit from thinner oil use. Over time permanent deposits of carbon and sludge build up in the engine oil ways. It is like a clogging of arteries in humans. We are now all on blood thinners. This is an area I specifically studied while a general surgeon resident at Chapel Hill. For those engines with excessive varnish and carbon buildup the engine oil additives of the detergent type may be of benefit. On the other hand you could just use a thin synthetic oil and change it every 200 miles for a while and end up with an even cleaner engine. With everything working properly you may actually need a thicker oil if that engine is overly worn. There is one more thing. A 20 weight oil is not half as thick as a 40 weight oil. The real scale is more like the oils having an absolute thickness of 108 and 114. Now it can be seen that the 40 weight oil is only around 10 percent thicker than the 20 weight oil. The difference is not that much at operation but at startup the difference is significant. Some think it is good to have a thicker oil for startup since the parts shrink when cold and would otherwise “rattle.” Sure, your piston diameter will shrink on cooling but so will the diameter of your bore. This is not true for your valves. They lengthen when extremely hot. In the Murcielago they use shims instead of self adjusting valve tappets. Here is an interesting tidbit of information. A 75W-90 gear oil has the same viscosity as a 10W-40 engine oil at 212 and 302 F. Once again, those numbers on that oil can are misleading and certainly add to the confusion I see among automotive enthusiasts. At 75 F gear oils are much thicker than motor oils. There are no start up issues so pour-point depressants are not added to minimize the thickening at ambient in gear oils. Chapter 9 - temp, viscosity, pressure, and flow comparisons We have seen that 0W-30, 5W-30, 10W-30 and straight 30 weight oils all have the exact same viscosity at 212 and 302 F. Do 0W-20, 0W-30, and 0W-40 all have the same viscosity at a 75 F startup? The answer is no. Viscosity at 75 F startup 0W-20.....0W-30......0W-40 40..........50............60 I give you the following example to help visualize what is happening. This assumes the oil has no internal resistance. In actuality doubling the pressure will not double the flow but will be slightly less. And thicker oils have more resistance than thinner oils for all situations. But simplified we get the following: 30 wt oil, operating temperature: RPM.......Pressure..Flow 1,000......20 PSI......1 2,000......40 PSI......2 4,000......80 PSI......4 8,000.....160 PSI......8 The maximum flow because of the oil pop off (bypass) valve at 90 PSI will be 5 30 wt oil, operating temperature, higher output oil pump: RPM........Pressure.....Flow 1,000......30 PSI........1.5 2,000......60 PSI........3 4,000......120 PSI......6 The maximum flow because of the oil pop off valve at 90 PSI will be 5 8,000......240 PSI......12 If we stick with the same weight oil and increase the oil pump output we will increase the pressure and the oil flow too. If we double the oil pump output we will double the pressure and we will double the oil flow (in an ideal system). RPM........Pressure.....Flow 1,000......40 PSI........2 2,000......80 PSI........4 4,000......160 PSI......8 The maximum flow because of the oil pop off valve at 90 PSI will be 5 8,000......320 PSI......16 40 wt oil, operating temperature: RPM....Pressure....Flow 1,000......30 PSI....1 2,000......60 PSI....2 4,000....120 PSI....4 The maximum flow because of the oil pop off valve at 90 PSI will be 3 8,000....240 PSI....8 40 wt oil, operating temperature, higher output oil pump: RPM.......Pressure.....Flow 1,000......45 PSI.......1.5 2,000......90 PSI.......3 The maximum flow because of the oil pop off valve at 90 PSI will be 3 4,000....180 PSI.......6 8,000... 360 PSI.......12 40 wt oil, operating temperature, reduced pressure: RPM....Pressure.......Flow 1,000......20 PSI......0.5 2,000......40 PSI......1 4,000......80 PSI......2 8,000... 160 PSI......4 The maximum flow because of the oil pop off valve at 90 PSI will be 3 Increasing the pressure while using the same oil will increase the oil flow but increasing the pressure by increasing the oil thickness will result in less flow. It takes more pressure to move a thicker oil. Pressure does not equal lubrication. Look at a single closed “lifetime lubricated” bearing hooked up to a system to pressurize the bearing. We could have the oil at ambient pressure. We could then double, triple, quadruple the pressure of the oil. The oil is non-compressible. Regardless of the pressure we would have the exact same lubrication, that of the ambient pressure lubrication. Chapter 10 - The graduate I am going to bring up the constant flow pump concept. Principle: the pressure of the same weight oil does not exactly double the flow but it is close, doubling the RPM for the same reason does not exactly double the flow but again it is close. Example: (A) 30 wt oil, operating temperature: RPM....Pressure......Flow 1,000......20 PSI.....1 2,000......40 PSI.....2 4,000......80 PSI.....4 8,000... 160 PSI.....8 The maximum flow because of the oil pop off valve at 90 PSI will be 5 ( 30 wt oil, operating temperature, higher output oil pump: RPM....Pressure......Flow 1,000......30 PSI.....1.5 2,000......60 PSI.....3 4,000....120 PSI.....6 The maximum flow because of the oil pop off valve at 90 PSI will be 5 8,000... 240 PSI.....12 © 40 wt oil, operating temperature: RPM....Pressure.....Flow 1,000......30 PSI....1 2,000......60 PSI....2 4,000....120 PSI....4 The maximum flow because of the oil pop off valve at 90 PSI will be 3 8,000....240 PSI....8 (D) 40 wt oil, operating temperature, higher output oil pump: RPM......Pressure.....Flow 1,000......45 PSI......1.5 2,000......90 PSI.......3 The maximum flow because of the oil pop off valve at 90 PSI will be 3 4,000....180 PSI.......6 8,000... 360 PSI......12 The situations (A) and © are close to real life, assuming no loss in the system. This is what happens when you change the 30 weight oil to a 40 weight oil in your car: At 6,000 RPM the maximum rate of flow has been reached with the thinner oil (A). When you go to 7, 8 or 9,000 RPM you do not get any more flow. You only get a maximum rate of 5. The internal forces on the bearings increase but there is no additional flow of oil. With the thicker oil you reach maximum flow at 3,000 RPM ©. Worse yet is that the maximum flow is now only 3. As we increase RPM to 4, 5, 6, 7, 8, 9,000 RPM we get no additional pressure and no additional flow, no increase in lubrication. Next let us look at a 20 weight oil at operating temperature. We get the same flow out of our constant volume pump but the thinner oil requires less pressure to move through the system. This even goes along with the rule that we should use an oil that gives us 10 PSI per 1,000 RPM: (E) RPM...Pressure....Flow 1,000......10 PSI.......1 2,000......20 PSI.......2 4,000......40 PSI.......4 8,000.. ...80 PSI.......8 The maximum flow rate has not been reached. If the engine went to 9,000 RPM then the flow would be 9 at 90 PSI, our maximum pressure at pop off (bypass). The engine now has 3 times the flow rate as with the 40 weight oil at full RPM. The nozzles at the bottom of each cylinder are spraying 3 times the amount of oil lubricating and cooling this section. Everything runs cooler and the separation forces in the bearings are 3 times higher. For engines that redline at 5,000 RPM they usually pop off the oil pressure at 50 to 60 PSI. For engines that go to 8-9,000 RPM the pressures max out at 90-100 PSI. You can now see that you can only get the maximum flow rate if you follow the 10 PSI per 1,000 RPM rule. So now you can see why I chose 0W-20 weight oil for my Maranello. I said earlier that I could use a 10 weight oil. I actually only run with 185 F oil temperature around town and the pressures are similar to the 40 weight oil example in © above. This is why I also said that in the racetrack condition, with hotter, thinner (0W-20) oil I may actually get the optimal results as in (E) above. The Ferrari recommended parameters in my 575 Maranello manual call for 75 PSI at 6,000 RPM. The pop off pressure has not been reached. As we now increase the RPM we still get an increase in flow rate. We get our maximum flow at the maximum system pressure, at about the maximum engine RPM of 7,700. There is no bypassing of the oil. All oil pumped goes through the system. There is no wasted BHP pumping oil past the bypass valve back to the oil tank. It is the perfect system. Now compare a single, 30 weight oil, at normal (212 F) and at racetrack (302 F) temperatures: (A) 30 wt oil at 212 F: RPM......Pressure.....Flow 1,000......20 PSI.......1 2,000......40 PSI.......2 4,000......80 PSI.......4 8,000... 160 PSI.......8 The maximum flow because of the oil pop off valve at 90 PSI will be 5 (F) 30 wt oil at 302 F: RPM.......Pressure.....Flow 1,000......10 PSI........1 2,000......20 PSI........2 4,000......40 PSI........4 8,000......80 PSI........8 The maximum flow because of the oil pop off valve at 90 PSI will be 9 The hotter (302 F) 30 weight oil is thinner than the cooler (212 F) 30 weight oil. It has the same flow rate in the constant volume oil pump but at a lower pressure than the oil at normal operating temperature. This allows for a doubling of the flow rate at peak RPM. The thinning of oil at higher temperatures is a benefit. You get more flow, more cooling and more lubrication. The 30 weight oil at 302 F has the exact same flow rate and pressures as the 20 weight oil at 212 F. See (E) above. Therefore, use the 20 weight for around town driving and the 30 weight on the hot track (in this example, your car may have different requirements). For YOUR engine, substitute the actual flow at 1,000 RPM. If your engine puts out 1.5 liters/min. at 1,000 RPM it would put out 3 liters/min. at 2,000 RPM and 6 liters/min. at 4,000 RPM and so on. The maximum flow in (A) would be 7.5 liters/min. In situations (E) and (F) you would get a maximum of 13.5 liters/min. Conclusions: Multigrade oils were developed to address the problem of oil thickening after engine shutdown. Over the years we have been able to reduce the amount of thickening that occurs. There is no oil that does not thicken after you turn your engine off. This is why we have to warm up our engines before revving them up. Engine designers always pick the recommended oil based on a hot engine and hot oil. There is no issue with oil thinning as they are both matched when hot. The problem is oil thickening when the engine cools. Cold engine: 40 wt oil, 75 F: RPM......Pressure.....Flow 1,000......60 PSI.......1 2,000....120 PSI.......2 The maximum flow because of the oil pop off valve at 90 PSI will be 1.5 4,000....240 PSI.......4 8,000....480 PSI.......8 At 1,500 RPM you reach the maximum oil flow rate and if you run to 8,000 RPM it is the same rate. The flow cannot increase and it is insufficient. This is why we must wait until our oil temperature comes up to 212 F or higher. The maximum flow rate in this case will then double, up to 3. To get even more flow in our test engine you need to use a lower viscosity grade. I showed evidence that the starting grade should always be 0 or 5 (0W-XX or 5W-XX for thicker oils). If you want the best protection and highest output from your motor use a synthetic based oil. The actual brand is not as critical as the viscosity. The rating must be SM. Change your oil every 3 - 5,000 miles and at least every spring. THE END Quote Link to comment Share on other sites More sharing options...
neotech84 Posted December 24, 2009 Share Posted December 24, 2009 WOW nice Quote Link to comment Share on other sites More sharing options...
FricFrac Posted December 25, 2009 Share Posted December 25, 2009 I had previously read the Oil 101 thread and its very good. I guess what I'm saying is that hot oil is a very broad and vauge term rather than stating the oil should be at operating temperature.... Quote Link to comment Share on other sites More sharing options...
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