Changing Oil: Hot or Cold

[zxtman]

I let the car sit overnight and change the oil cold the next day. When you shut down the engine the oil is hot and drains into the pan: all the oil that will make its way to the pan, does so.

 

Why would you start-up the engine to heat-up the oil just to drain it? Not all of the oil will have made its way into the pan.

This makes no sense to me.

 

Besides, who enjoys doing a hot oil change!?

[johnc]

This is all IMHO...

 

Using an engine cleaner, ATF, or diesel fuel to clean the internals of an engine is a waste of time and money. It may have been of some use "back in the day" but since then, engine oil cleaning ability has improved by orders of magnitude and, more importantly, gasoline is better refined and has detergent packages that have significantly reduced the dirt that gets into engines.

 

I just pulled the cam covers on the V10 in my 2000 F350 which has 105K miles on it. Its had regular synthetic oil changes (every 5,000 to 7,500 miles) and unleaded regular fuel run through it the entire time. No cleaners, ATF, or diesel fuel ever. The cams and valvetrain looked brand new with no deposits or varnish of any kind.

[Hyuri]

I prefer changing the oil warm, but I've never had a problem with getting oil all over myself since I learned one simple trick: keep constant, firm but not heavy, pressure on the plug as you unscrew it by hand. Do that until it's completely cleared the threads, then yank it away to the side: if you do it fast enough, your hands will stay completely dry.

[srbigbutt]

I prefer changing the oil warm, but I've never had a problem with getting oil all over myself since I learned one simple trick: keep constant, firm but not heavy, pressure on the plug as you unscrew it by hand. Do that until it's completely cleared the threads, then yank it away to the side: if you do it fast enough, your hands will stay completely dry.

 

I learned that trick as well!! haha. It only took me about 10 years!!

[patzky1]

So simple... just give it 10-20 minutes after running at operating temp (usually enough time to drink at least one beer) before changing it. That way IMHO, the oil has drained back to the pan AND it is still warm enough to flow quickly enough to bring out any crud.

[grumpyvette]

the IDEA is to have as much crud held in suspension when the oils drained as possiable when the plug is removed so that as much crud flows out with the oil as its drained as possiable, that will require the engine oil to have been heated and flowing recently so the loose cruds been recently stirred and mixed, rather than having settled out over night and when the oils thicker and colder, thus allowing some crud to stay on the oil pan floor.......think IM wrong!

try getting a pair of CLEAR glass jars,after running the engine for 5 minutes the night before then turn it off, drain THE first pint of hot oil into one , then put the plug back and drain the NEXT pint the next morning, after taking the second sample let the rest drain into the usually oil pan, lable both, then pour out both into the oil pan and look at whats left in the glass containers, DON,T use the last qt drained hot or cold , as that last qts bound to have more crud than the first with EITHER methoed.

what youll find is that oil that sits awhile and cools allows some crud to settle out to the oil pan floor, crud that gets put back into suspension when the engines been recently run, and before someone points out that the oil filter is supposed to trap and remove suspended crud, yes thats true, but oil filters rarely get 100% of the crud and the older the filter the more it gets restrictive to flow and the more likely its BYEPASSING a certain percentage of the oil flow untill the oil heats and looses some viscosity

 

easily 10%-20% of your oil byepasses the stock filter if you rev the engine while its still cold

[JSM]

Grumpy,

 

I understand your example and explanation.

 

Now if you compared what is in hot oil with suspended particals trapped (or not in the pan yet) versus sitting at the bottom of the pan cold, which would be more?

 

This whole topic may be a waste of time as there may not be much evidence in wear to support either method of oil changes.

 

Just change your oil regularly and don't lose sleep over it, right?! I was more curious then anything.

 

This past weekend change was done after sitting an hour. Just worked out that way.

[grumpyvette]

Grumpy,

 

 

This whole topic may be a waste of time as there may not be much evidence in wear to support either method of oil changes.

 

Just change your oil regularly and don't lose sleep over it, right?! I was more curious then anything.

 

QUOTE]

 

YOUR CORRECT THERE ARE FAR MORE CRITICAL things to worry about, change the oil and filter either way every 3500-5000 miles and your very unlikey to have problems, "its a TEMPEST IN A TEAPOT" or as they say, "much sound and fury signifying nothing"

[biohazard53188]

My dad is a Mechanical engineer in his late 60's. He always told me to change the oil when it is cold so all the used oil can settle in the pan and it is much easier to work on.

 

I'm curious if doing this cold could cause more wear to the motor, being that once drained and cold, oil presure is needed to be built up before parts begin to be lubricated. Where as warm, everything has a nice coating from recently being run.

 

Thoughts? Or even if there is more wear, the difference is not significant.

 

Changing the oil hot is a much better idea. It will get all of the gunk off the sides of the oil pan/crankcase. If you let the engine sit some deposits can form and will not drain out with the cold oil.

[Tony D]

The problem with cold oil is that not only has all the oil settled to the crankcase, all the particulates in the oil have settled and gotten adhered to the pan! Then when you drain the cold oil, it simply leaves that sludge behind, waiting for the next agitation with hot oil to whip it back up into your new, fresh, oil.

 

The ammount of oil you will drain out compared to doing it hot, with all oil contaminants in fresh suspension, is so insignificant as to be inconsequential.

 

But the benefit of draining hot oil with all the contaminants in suspension and ready to come flowing out at a faster rate and lower viscosity is significant.

 

I don't know of one OEM that specifies oil analysis samples to be pulled from an ICE with oil cold. They want it HOT, because that will give them a representative example of particulates, contaminants, etc without any possibility of them falling out of suspension and settling to the pan.

 

I, too, am curious as to the logic espoused. "Get out all the old oil" is a rationale, but sketchy at best. "Get out as much of the contaminants that would affect the new oil" is a far better logic to use...and which will dictate hot oil changes.

 

Always replace the filter when changing oil, as Grumpy stated, it can bypass, and an older filter while holding a bunch of patticulate laden oil in there can also bypass due to pressure drop at a lower pressure than you may think---causing bearing polishing and other issues.

 

On high-speed rotating compressors, we will change filters only 4X annually. Those filters are sent to labs for analysis of particulates in the pleating. The oil will be sampled every 1000 hours (monthly or thereabouts).

 

Then again, they are twisting 74K rpms in some cases...and micronic particles can do lots of damage at that speed. When a filter bypasses on those due to plugging, bad things are precipitated...in short order!

 

There is a lot to be said for John C's comment about new synthetics, or newer oils in general being much more resistant to sludge formation that they have been in the past. The deposits of yesterday were a product of poor ring seal and bad things in the fuel, as well as relatively poor fuel mixture control. It was not uncommon to have to worry about 'fuel dilution' in the days of carbs running in cooler climates and 160 degree thermostats. The good old days weren't...and in many cases today we are much better off dealing with fluids for our vehicles that are much more 'proper' in their forumlation for aparticular application than they ever were before. This goes a long way towards preventing the problems of the past.