Pratical oxidation avoidance

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The best way to avoid a very common engine oil oxidation source, is to let the engine shed the heat from the piston crown, by idling it for a minute+ before shutting it down. If you came from a highway, running at 85mph, put the car on the rest area and shoot the engine down, that's a nonono. You can get about 150F temperature decrease with that practice and won't boil the oil in the ring pack area every time you turn the engine off. That heat will go to the coolant and you'll feel the engine hotter, but the pistons,rings and the accompany oil, will not be hotter. Such oil boiling makes the most crud on mineral oils. while the engine is running tha volume is constantly changed by fresh or cooler oil. And, rememmber at shut down, that every 10 degrees of temperature hotter, will cut the oil oxidation capacity to the half, imagine that volume at 400 instead of 250 ... That volume (about one ounce or so) could be toast by a bad practice.

Synthetic oil withstand much better this condtion, but why stress the thing ...

You get the oil a little darker (by oxidation stand point, not for the cleaning agent detergents), every time the engine don't get the excess heat spread form the pistons (the main heat source) to the coolant. Yes, what makes oil darker is also the shut down.

Critics, come by, and have coffee...
 
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You're assuming that color is related to oxidation, which it isn't necessarily. You're also assuming that the latent heat in the piston, which can only possibly decrease in total energy (even if transport shows a temporary rise) can do something that exposure to combustion conditions can't. Finally, you're assuming that there is sufficient oxygen stoichiometry to do this, for a duration, and with enough oxygen transport to do more than just oxidize the atoms exposed in the surface.

And I think you're confusing oxidation for pyrolysis or some other high temperature mechanism..
 
I'm assuming, yes!
Tell me:
1) oil oxidation (by heat) without darkening;
2) a temporary what: 4-5 minutes excess heat over boiling point to be transported, won't do any harm to the oil for your assumptions;
3) you have air between rings and the oil has a bunch of air bubble that will purge in that area (antifoam acting here the bubbles form, just won't endure a lot), feeeding the process, a lot, IMO beyong the atoms exposed on the surface.
 
450 F at crown (average, central superior part get 550F), less at skirt, giving an average of what 400 at ring pack. The boiling point (not flash) of mineral oil is about 300.
 
Given that the oil in the ring belt is there for 10s of seconds, and the ring belt is well over 150C, part of the oil is always at that temperature.

Given also that (for example in my Caprice), the oil being flung from the big end bearings is similarly, well over 100C (I can get to 135C by holding it in "2" and 4,000RPM for a few minutes, I don't think that idling for a few extra minutes is going to make much if any difference in the oxidation life of an engine oil.

You've got me pondering what the chemical composition of blowby gasses is 'though.
 
Originally Posted By: Pontual
450 F at crown (average, central superior part get 550F), less at skirt, giving an average of what 400 at ring pack. The boiling point (not flash) of mineral oil is about 300.


That's why NOAK is done at 250C

300F is only 150C...I think you are a bit low on your estimate of lubricant boiling point
 
Well blowby come from the top, air comes from the bottom of the piston, there is more from the bottom than from the top, specially between oil control and compression rings. The temperature you said is conservative and the time that the oil is exposed with the engine running is very short, because of the substitution from pressurized system.
When you shut down the substitution ceases and the portion will suffer much more than 10 seconds, I believe.
 
Do you really know how a NOAK is done ... There FYI, the disc is turning and the oil is flowing, none of these conditions are seen in the ring pack when the engine is off!
 
I would wonder if the piston would heat up more at idle. At idle it will spend more time at top dead center than at say 3000 rpm. If it sits at top dead center longer during the combustion phase, would it not absorb more heat, than it would at 3000 rpm where the heat goes out the exhaust valve?

Now with a turbo, i would agree with the idle recommendation for the turbo.
 
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No is the answer for the question (heat production is minimal with engine idleing and having no load) the piston crown you get from 260C to 140C and that spread to skirts and out to the liner and quickly will get 100 with engine off, a much smaller step. And yes for the affirmative, turbo will also benefit from idling.
 
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Are you using olive oil as motor oil??

The canola oil that I use for deep frying withstands 465 F before it starts oxidizing, I assume that engine oil resist a little bit more. Your estimates for piston temperature seem a little higher to me, The temperature of the pistons commonly reported is 356F. I would worry more about the oil left in the cylinder wall, that its is partially combusted and then it is washed again into the oil.
 
You're talking about imediate oxidation. and there is a kind of oxidation called gradual. Yes 450F would toast mineral oil, also sofisms appart. I've an study here at bitog about oil temperatures, and the crown temperature of a jag V8 at 5k rpms, was 318C, that's way more than 365F. You're idling before the measurement, huh, rsrsrs
 
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I know diesel engines its good to idle them down, but I know my motorcycle if you let idle, water temp sky rockets pretty quickly. Im sure some cars too, I guess it depends on the particular motor, if any value in idling down.
 
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Great your insite. And that confirms the whole situation! The heat goes from the parts (pistons - combustion chamber) to the coolant by the rings and liners, also to the oil, but the important is to take the heat off, from the pistons and cc ...
 
Just one of the many reasons to use a quality synthetic oil. Resist oxidation better than dino.
 
You mention boiling. This has nothing to do with oxidation. Also you are ignoring the add pack which has antioxidants.
 
Originally Posted By: Pontual
You're talking about imediate oxidation. and there is a kind of oxidation called gradual. Yes 450F would toast mineral oil, also sofisms appart. I've an study here at bitog about oil temperatures, and the crown temperature of a jag V8 at 5k rpms, was 318C, that's way more than 365F. You're idling before the measurement, huh, rsrsrs
with a crown temperature that high, wouldn't that put the aluminium in the recrystallization (annealing) zone that will lead to a catastrophic failure??
 
No, it is 450C, not 450F the Al problem. And Nate79, the antioxidants will give more time, but that's depleteable pretty quick under certain conditions.
 
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