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L28ET - Suddenly 0 oil pressure (Not a faulty gauge!) *SOLVED*


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You're welcome to put 5w-30 in a 150,000 mile Z car and I will bet it has near zero oil pressure at idle when warm.

 

My point is that it was too thin for the application.

 

Probably too thin for a high mileage L28 as well.

I didn't see that point at all in your previous post. No one, including you, ever mentioned using 5W-30 in an L-series.

 

First off, you said:

 

Careful with the thin oil like 10w-30.

Not sure where this warning comes from, as there is no merit behind it. In fact, that is a recommended viscosity in the FSM. Then you go off on a tangent about some guy putting the wrong oil in his car.

 

FWIW, I use a fully synthetic 10W-30 in my nicely running, beaten up, who-knows-how-many-miles L24. No issues for over the 2 years and thousands of miles. That reminds me, I need to change the oil!

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I was referencing the "30" at the end of "10w-30 and related an experience of "5w-30" being too thin when warm.

 

The "5w" and "10w" apply to the viscosity rating when cold or "w" for winter.

 

The "30" applies to the viscosity rating at operating temperature.

 

Since my reference was only to a low pressure issue at operating temperature, the "10w" and "5w" have zero difference in my reference and you should only look at the last number.

 

Sure, you didn't have problems with an 30 weight oil at operating temperature but I was posting an issue that could possibly rear it's head in a high mileage L28.

 

I fully know what nissan specified for the L28 as I have been a nissan dealership master technician since the early 90s and have been wrenching them at various independents since 1979.

 

That said, I've been running 20w-50 oil in my L28s for about 300,000 miles and over 20 years..........but I have run into plenty of L series engines that will light the low oil pressure idiot light at idle when running on an oil with a "30" at the end and that simply switching to 20w-50 got rid of the light, moved the needle into a safe pressure, and allowed the engine to still be running 15 years later without a rebuild.

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I realize we're diverging from the original topic now, but as OP's issue has been resolved, seems like it's ok to explore...

 

Aren't we missing the bigger picture here? Isn't what matters here that an adequate VOLUME of oil gets to all the lubricated surfaces?. Given that it's difficult and expensive to measure volume, didn't the designers instead choose to measure PRESSURE and assume that as long as the pressure is adequate, the volume will be too? That would seem to work as long as the viscosity of the oil is within the range for which the system is calibrated.

 

Assuming that is correct, then can we also assume that if the pressure is low, that the volume must be low? I think this is where we need more information. I've often wondered if there is any data that shows that by using a thicker oil which results in higher measured pressure, if any more oil actually reaches the surfaces? (I'm deliberately ignoring having adequate pressure to pump up valve lifters as our older Zs don't have them). Alternatively, if the oil is very thin (say 0 weight) we expect the pressure to be lower than with a thicker oil, but how do we know that this means there isn't perhaps MORE oil making it the surfaces?

 

As the saying goes, inquiring minds want to know ...

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If number 6 rod starts to knock, you don't have enough volume or pressure. :-)

 

I ran 5W-30 in my race engine with about 100psi of oil pressure at 7,000 rpm. I could have a run a 0W-20 with the oil pump I had. Just shim the oil pressure spring if you're worried about the idiot light at idle.

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volume is the amount of space occupied by a given substance, pressure is the amount of force applied by a substance in a given space(volume), however pressure and volume do correlate, having volume does not give you indiscriminate pressure. Example a run flat(I'm using run flat since the side wall has no deflection when empty) tire at 35psi has a volume of 2cubic feet, a tire with 0psi still have a volume of 2 cubic feet. Both spaces are occupied by by air, but at different pressure because the KEY is density. Going back to oil, the weight of oils have different density, that causes direct effect on pressure inside the engine and oil passages. Just because air, or oil makes contact with a surface doesn't mean the do the same thing at varying pressures.

 

Also volume in a metallic solid is static, until pressure exceeds the tolerance of the solid and causes it to burst like a balloon, this is why oil is measured in pressure, if volume was measured the "space" occupied by oil would be a constant during engine operation.

 

Large oil pumps increase volume of oil flow, but that in turn with the internal friction and density of the oil causes compression of the oil in the motor, liquids do not like to be compressed so that will increase oil pressure.

Larger volume in between bearings and gallies will reduce oil pressure, thus reducing the oil's need to reduce pressure and to travel to other paths of least resistance. Oil is forced though bearing surfaces because the pressure of the oil is higher of that of the low/no pressure areas crankcase or valve train.

Edited by shri2222
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volume is the amount of space occupied by a given substance, pressure is the amount of force applied by a substance in a given space(volume), however pressure and volume do correlate, having volume does not give you indiscriminate pressure. Example a run flat(I'm using run flat since the side wall has no deflection when empty) tire at 35psi has a volume of 2cubic feet, a tire with 0psi still have a volume of 2 cubic feet. Both spaces are occupied by by air, but at different pressure because the KEY is density. Going back to oil, the weight of oils have different density, that causes direct effect on pressure inside the engine and oil passages. Just because air, or oil makes contact with a surface doesn't mean the do the same thing at varying pressures.

 

Also volume in a metallic solid is static, until pressure exceeds the tolerance of the solid and causes it to burst like a balloon, this is why oil is measured in pressure, if volume was measured the "space" occupied by oil would be a constant during engine operation.

 

Large oil pumps increase volume of oil flow, but that in turn with the internal friction and density of the oil causes compression of the oil in the motor, liquids do not like to be compressed so that will increase oil pressure.

Larger volume in between bearings and gallies will reduce oil pressure, thus reducing the oil's need to reduce pressure and to travel to other paths of least resistance. Oil is forced though bearing surfaces because the pressure of the oil is higher of that of the low/no pressure areas crankcase or valve train.

 

What you say is true, but the problem with the air in a tire analogy is that you are using a compressible fluid (air in this case) and oil is essentially uncompressable. So the amount of oil in a given volume at 0 psi is essentially the same as at 35 psi.

 

So my question remains: all else being equal, in our L engines, does using a lower viscosity oil result in more or less VOLUME of oil being delivered to the lubricating surfaces?

Edited by Zmanco
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That would have to deal with the flow rate of the pump. If its rated at 100gph at 5000 rpm, it should flow at 100gph regardless of the viscosity, unless the clearances of the pump aren't tight and the thinner oil can bypass the pump mechanism.

 

By no means fact, just my understanding of fluid.

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Flow rate is also at some psi number. You can't have flow at 0 psi or there would be nothing to impart flow. There has to be pressure (or pressure differential) to get a fluid to flow - unless you're talking about thermodynamics.

 

True, but if you dump a Gatorade tub on a coach, you have high flow at a very minuscule psi. Once again, not saying im anywhere near an expert.

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What you say is true, but the problem with the air in a tire analogy is that you are using a compressible fluid (air in this case) and oil is essentially uncompressable. So the amount of oil in a given volume at 0 psi is essentially the same as at 35 psi.

 

So my question remains: all else being equal, in our L engines, does using a lower viscosity oil result in more or less VOLUME of oil being delivered to the lubricating surfaces?

 

useing a lower viscosity oil will and should not effect volume, that would still be constant. What would change is the force and speed the oil moves though the engine, a lower viscosity oil will travel faster due to its lower desity. A lower density oil will have lower oil pressure, that pressure in the same volume will be more subseptible to displacement. Pressureised oil prevents bearing surfances from comming into contact with eachother, pressurised oil vs low pressure oil, would occupy the same space, but as a boat floats on water in comparison to its desity and weight, pressurised oil keeps the bearing floating. Low oil pressure hence can cause bearing failure.

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What you say is true, but the problem with the air in a tire analogy is that you are using a compressible fluid (air in this case) and oil is essentially uncompressable. So the amount of oil in a given volume at 0 psi is essentially the same as at 35 psi.

 

So my question remains: all else being equal, in our L engines, does using a lower viscosity oil result in more or less VOLUME of oil being delivered to the lubricating surfaces?

 

The viscosity has ABSOLUTELY NOTHING to do with the VOLUME DELIVERED.

 

This is almost a purely mechanical derivitave of the oil pump's capacity. The oil pump moves X cc's of displacement per 360degrees of movement. The volume displaced is that volume multiplied by the pumps input shaft speed.

 

Oil the thickness of tar may have a priming / pickup problem... But once flowing it will be delivered at the exact same volume by the pump as 0W-100 Super Synthetic.

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Pressure is resistance to flow. Thicker oil has more resistance and pressure builds, indicated by instruments.

 

As mentioned this also takes more horsepower to drive the oil pump with this thicker oil.

 

As engines wear, clearances increase allowing for more potential flow across that "orifice" this shows on institments as a "pressure loss" when in fact flow through the bearing juncture has actually increased.

 

"But Tony, you just said a pump is a mechanical device limited to a set flow curve by its internal capacity!"

 

And so it is.

 

It is also routinely so oversized for the application it's not funny. As the engine wears, in reality what is dumped overboard through the pumps relief valve just gets less and less. This allows full pump flow to the bearings and indicated pressure remains constant.

 

This is why bearings with wider clearances don't overheat, they have plenty of cooling oil flow across their working surfaces.

 

As John C says "shim the pump relief spring if you want mor pressure" -- what

You do is simply

Put the full pumps capacity to the ENGINE BEARINGS and not dump it overboard back to the sump.

 

Increasing the viscosity is generally not something recommended unless you have very specific application needs. Street cars are wasting money. Straight 30 or 40 is fully acceptable in less variable environments like where I live.

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As to VW's and oil weight, like most GERMAN engineered things, if you deviate from the engineered specifications, you run the risk of catastrophic damage.

When VW or BMW says an oil weight, they MEAN it.

 

What VW or BMW say doesn't apply to a Nissan, or a Ford. Each application has it's own engineering rationale.

 

Air Cooled VW's were notorious for scuffing cylinders and bearing breakdown when you ran other than the originally designated 30Wt (Straight!)

 

Atlas Copco air compressors did things which confounded simple observations when synthetic or off-weight oils were used. For instance, run an ISOVG32 Mineral Oil (20Wt) and all was good. Cold to hot the oil pressure would go high to low as one would logically expect. Put almost any synthetic and it had trouble not tripping on low oil pressure when cold, and setting off 'high oil pressure' when warm. Cutting and shimming the oil pump was an exercise in futility as the flow on the bypass leg was calibrated for maximum flow with mineral oil, not the dynamics of synthetics.

 

Oil is VERY misunderstood, how it works, how it acts and behaves, what you really want or need.

 

This was so important for VW in the Air Cooled Days, field trainers would spend almost 40 hours training distribution mechanics on proper lubricants and why you needed the ones VW Specified.

 

Apparently little has changed in their design philosophy, they engineer for X, and expect you to use X. If you use Y, and it doesn't work like X, they will give a typical German response: "It isn't X, what did you expect?!"

They do have a point!

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