Why is my oil temp so hot?

[Admin]

In the Media section today:

 

http://www.recreationalflying.com/threads/ask-paul-why-is-my-oil-temp-so-hot.29540/

 

 

[facthunter]

it's worth a read/ There's also an other question on leaning out on take-off/

 

The cure for high oil temps ( well at least the first technique to try, is to increase climb speed. If you have to clear terrain don't do it if you must have the climb performance.. Nev

 

 

[old man emu]

Paul McBride is a bloke who is worth listening to. We often give him a call when we have an odd engine problem. It pays to go to Oshkosh and meet people!

 

OME

 

 

[Vev]

Personally I like to see engine lube sump temps between 80 - 100 c

 

Engine lubes will hang together in terms of the chemistry out to 160- 180 deg c depending on the base stock oil used, however anything over 110 deg (sump temp) usually suggest the lube is being exposed to temp spikes (ie in the rocker chest) ... this will cause a potential for cracking the base oil and causing oxidisation issues.

 

Equally, very cool oil is not idea either, as it can hold water and not activate the additive package in the lube to give proper performance or protection.

 

It's a bit like the story of the 3 bears ... not too hot, not too cold but just right!

 

Cheers

 

Vev

 

 

[facthunter]

He does seem very sensible in a world where spectacular and radical ideas without much substance get too prominent a run. Good commonsense and advice based on experience is what you need.

 

Going to the oil temp specifically, hot running engines remain the cleanest internally. As Vev says run them too cold and you will get water remauining. Where doest the water come from? It's in the condensate of the blow-by gases mainly. It doesn't come from the air.

 

When hydrocarbons burn they become CO2 and H2O (water, and quite alot of it). Run the engine hot and it goes out the breather. ( the best place for it). Don't run it hot enough and it accumulates in the oil forming acids and sludge

 

Very hot parts of the engine, ie the underside of pistons and in air cooled engine rocker boxes, which runs at the temperature of the cyl head, which is really at the upper limit of where the oil can stay stable or above, is not good for the oil either.This is a local overheating and doesn't register on the temp gauge, but contributes to oil deterioration.

 

Vev works in the game so he knows what he is talking about. Nev

 

 

[Tomo]

Wonder what the leak down would be on that engine?

 

Engines with higher blow by than normal get hotter oil temps.

 

 

[facthunter]

I think that the motor in question was normal..

 

" Unclean" contaminated coolers are more likely to be a cause. If an engine had enough blowby to cause a significant rise in oil temp ( and it could) It would already be unsuitable for aero use as the "leakdown " is specifically monitored, and has a pretty high "reject" figure.. Any power loss within the engine will result in extra heat. Nev

 

 

[Tomo]

Yes that is true I guess.

 

 

[facthunter]

There would be no harm in checking it. Your point is completely valid. In a high power diesel it could herald an immenent engine failure. Nev

 

 

[fly_tornado]

Can I ask a technical question: How should one clean one's oil coolers?

 

 

[facthunter]

There are people who specialize in it apparently. Nev

 

 

[fly_tornado]

I assume they flush the inside with something and replace that bent up metal between the pipes.

 

 

[facthunter]

They used to use honeycomb (soldered together). That's almost impossible to clean, properly. The bigworry would be loosening some of the sludge and not getting it out and having it move later. Oil coolers are another thing to go wrong. Some engines get away without having to use one. (Preferred). Nev

 

 

[Tomo]

Back flush usually. If the fins are to damaged it's probably cheaper to get a new one. Though it's surprising how you can straighten it out most times. I've never done aircraft coolers, but car/ag machinery... not sure if there's any difference other than size.

 

 

[fly_tornado]

My BMW has 2 oil pumps, one high pressure for the engine and the low pressure one dedicated to coiling the oil down. The standard oil coolers are pretty small and I am going to use 2 to keep it under temp. Just curious if I should clean them first as there is a residual amount that gets left in the coolers that probably traps gunk. Would kerosene be adequate or should I look @ a degreaser?

 

 

[facthunter]

Kero won't do much . There are hot and cold degreasers. proprietary). You would have to have some means of circulating the solvent,( preferably backwards although where there are no real particles involved (just sludge) it would not be critical . A lot depends on whether you have one tube ot a matrix, where the fluid could go through mulltiple paths. What evidence do you have of sludge being in the coolers? Nev

 

 

[Tomo]

You'd want something a bit more abrasive than Kero. Cheap way of doing it would be just using petrol, and it evaporates - soak it in it if necessary so soften any sludge.

 

Mind you I'm no expert! If there are any signs of metal through the cooler you'd want to toss it to play it safe.

 

 

[fly_tornado]

I'll try some petrol. see how that works out.

 

 

[turboplanner]

You're all kidding right?

 

This is aviation, you flush them by replacing them with new ones.

 

That eliminates the sludge slugs and flakes which can cost you an engine.

 

 

[facthunter]

Turbo's right . There has to be no doubt with a thing that is in the oil line between the pump and the engine. Old engines that have sat for a while and then re-activated often have dislodged sludge block oilways or score bearings etc and the engine can fail completely. Have it done professionally or replace. Maybe they clean it by high frequency vibrations, like descaling blocks. Don't chance it. Nev

 

 

[Guest ozzie]

Oil coolers in the big boys toys are flushed then X Rayed for metal particles/blockages. You can get a small ali tube and put a small slit in it and use it as a tool to straighten the cooling fins.

 

Wasn't to impressed with those repco types when i replaced one on a jab storch. Better to get a custom stronger one built that's more efficient.

 

I found these in my travels. oil filter cooler.

 

Ozzie

 

 

[J170 Owner]

I'm afraid all this oil techo mumbo-jumbo is a turnoff for those who just want to fly as recreational pilots. I know "oils aint oils" but hells bells..... (Scroll bar still not working)

 

 

[Sapphire]

I think that the motor in question was normal.." Unclean" contaminated coolers are more likely to be a cause. If an engine had enough blowby to cause a significant rise in oil temp ( and it could) It would already be unsuitable for aero use as the "leakdown " is specifically monitored, and has a pretty high "reject" figure.. Any power loss within the engine will result in extra heat. Nev

The minimum on a leakdown test is considered 60 over 80 which, without doing a lot of math calculations, is a fair bit of leakage. If you get 80 over 80 then the leakage of the engine is equal or less than the leakage through the instrument's constricter. Only as this significant leakage increases does your needle start to move on your right hand guage.

 

 

[eightyknots]

They used to use honeycomb (soldered together). That's almost impossible to clean, properly. The bigworry would be loosening some of the sludge and not getting it out and having it move later. Oil coolers are another thing to go wrong. Some engines get away without having to use one. (Preferred). Nev

The old KISS principle applies here. But, what does one do about persistent high oil temperatures if you want to avoid an oil cooler installation? I can't think of a straightforwards solution.

 

 

[frank marriott]

I change oil and filter every 25 hours hopefully keeping the oil cooler clean. I am a pilot and NOT a LAME or L2 so I am doing what others have recommended to me.

 

Leak down check every 50 hrs. Monitor temps.

 

Is this reasonable to assume all is well?