Does hot oil create more heat? Please Speculate!

[Killerbees]

Before us today is a vehicle that is max performed. The oil regularly climbs above 240, and occasionally sees up to 380 degrees. Obviously there is a cooling problem.

Not concerned with that now.

What I would like, is to hear open opinions on

what degree of ADDITIONAL heat production occurs, resulting from friction, due the loss of lubricity at elevated oil temps.

Back it up if you can, but don't let lack of data stop you. Unqualified opinions
..............

, LOL.

 

[bruce381]

other than piston/rings there is not a lot of friction as in rubbing stuff in a running engine in good shape so I have no clue.
bruce

 

[Gary Allan]

I would ask what your pressure loss is due to oil temp. Anything above 302F ..you've got to be at near 1-2 CST ..or so I would imagine ..maybe fractional CST (

)

 

[Gary Allan]

Make that about 4.2 CST @ 340 using Delvac 1 as a standard for visc

 

[Pablo]

Ever see an oil starved crank? NOW that, my speculating apprentice, got hot!

 

[Killerbees]

Right on, 4-5 cSt. Pressure goes from 55 @ 200 F, to 30 @ 320 F (est). Sound right?

So what is the harm (heat) in 4 cSt when designed for 10-15?

Let's get some juicey opinions here.

 

[LarryL]

The heat might effect other things, too, which will turn back on the oil temp and the circle could defeat the engine. There may not be one thing to single out, once the process gets going. You might have bearing damage caused by detonation caused by coolant temp that drove the oil temp up, too. Excessive oil temp like you describe could be caused by more than one thing. Looking at just a lubrication failure could cause you to miss the problem. Do you have more information?

 

[Gary Allan]

Well, I wouldn't think (I'm out of my environment with diesels) that I'd worry from a pressure stand point. The oil is definitely looking at a shorter life. You're getting into, IIRC, bearing damaging temp range.

(I googled it to verify before I shot my mouth off

This doesn't directly relate --but

)

Tin and lead babbitts commonly used in oil-film bearings, for example, start to plastically flow when local fluid pressure approaches compressive yield strength. This can happen even under normal loads when operating temperatures reach about 300°F. Therefore, keep peak temperatures below 250 to 275°F in such bearings to allow for transient loads.

just the ref

 

[Gary Allan]

Larry, he's got ramrodding drivers yahoo'ing it up 8% grades as fast as they can to make their log book pay out the most miles before they're shut down on a 70 hour week ..is what he has.

 

[Killerbees]

True, these are diesel vehicles running WOT, with more than one area for improvement. They are apparently a tidbit shy on a full cooling rejection capability. Best estimates, 5-10% additional cooling would contain it. IOW, I have a 650,000 BTU/hr motor, with 600,000 BTU/hr rejection capacity.

But I'm not trying to solve that in this thread, just discuss the possible thermally spiraling contribution of the cycle.

"Do increasing oil temps lead to more heat rejection deficit"?

Good responses, keep it going.

 

[Gary Allan]

I'd say - yes ..but it obviously isn't of long enough duration or extreme enough in severity to cause the "thermal spiral of death" one usually associates with regenerative aspects to oil temp. You've got something catching it before the bottom drops out.

You've got quite a bit of cross thermal exchange there. It's hard to NOT have oil temps lead to more rejection deficit. I think the real question is if it's a causal or a resultant event. I'd say that initially it's a victim ..at a certain point ..an accomplis. Once you're out of control, it gets kinda blurred.

 

[Killerbees]

NO!... We overheat. Definately, death.

"I think the real question is if it's a causal or a resultant event."

guess, speculate, find me a cooling engineer!

 

[Gary Allan]

How about a PCM controlled govenor??

Gosh I wish XS650 and 427Z06 were active now. They would have some worthwhile input for you from an engineering stand point.

I'll see if I can bring them out of the BITOG rehab.

 

[oilyriser]

Perhaps the hot oil is draining off the oil cooled pistons, and the bearings are not quite so bad off as it seems. If the oil is draining off at 380 degrees, the pistons must be getting really hot, and might be causing the oil to carbonize. That would be a bad thing.

 

[Mr Nice]

On average.....How much hotter is the oil temp (non Turbo engine) than the coolant temp ?

 

[Gary Allan]

I'd say +/- 25Fi for most gas engines under most conditions.. NA or turbo. Racing or "altered states" will elevate both above that at times.

 

[Killerbees]

I would say, non-turbo, non diesels, see 20 degrees over coolant temps.

Forced induction, heavy load vehicles like this see oil used much more as a coolant. And there is a cooler, that exchanges with coolant. Trouble is the coolant is not contained either.

Back to the question. What evidence/empiracal data/rationalle can we assert to demonstrate that hot oil creates more friction?

Don't need to solve the problem just yet. Need to qualify all aspects of the problem first.

 

[Gary Allan]

I don't see that it does. I've basically ignored most of the whiz bang and what to of film theory and whatnot since, in my current state of need, I just trump everything I encounter with "more". I'll never see 150C to test our HT/HS ratings.

My osmotic uptake on this would reason that hot oil doesn't, just by being hot oil, create more friction. I'm sure that there are number of "qualifiers" involved that could alter that statement.

You've got a situation of two cooling mediums competing for the same turf ..and both are saturated. The excessive temp(s) is/are the backlog of btu's to be processed. Normally the differential would just keep climbing until the rate of exchange could establish an equalibrium of production and rejection. Your system just doesn't have a peak temp capacity that can allow that to occur.

 

[Gary Allan]

Pondering some things here that were inspired by my last post.....


Have you considered PG coolant? That has a boiling point of 375F (IIRC). That would probably manipulate your btu rejection rate upward. Since you're down to 30 psi, you've got substantial room for effects of intermediate cooler pressure alterations (which I really feel need to get off the drawing board and into the living lab to be realized).

 

[Killerbees]

Yes, it doesn't matter. Vehicle brain limps the motors at 250, regardless of what it drinks. Don't think we like the much reduced heat transfer coefficient, and double viscosity. Nothing but problems

Pure EG also has high BP. another whole can of worms.

(unless I can put it in the crankcase)

Please refer to topic title.