What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Excessively high oil temperature (400+ degrees)

In an attempt to clear some fouled plugs, my partner ran the engine in the runup very lean for a while and said he saw the oil temp above 400 degrees before he realized and pulled the power. Engine is an Aerosport IO-360 with dual electronic ignition and automotive BR8EIX plugs.

1) Is an oil temp of 400 degrees even possible without causing a fire? I'd have thought CHTs would have exploded well before oil ever got that hot.
2) What kind of damage could be possible if it did actually hit that temp? The plane is currently grounded at an airport about an hour away from home and I'd like to bring it back where we can work on it, but I'm afraid to hop in without knowing what could have been damaged that may not be caught in a standard runup.
 
At that temperature I'd think the oil would start to carbonize and burn. Not a flame burn, but smoke point. You'd have dark black, burnt smelling oil. I'd drain a sample to see, but expect that the temperature probe is reading incorrectly and the oil (and engine) is fine.

Check the probe for accuracy and probably good to know.

On a similar note, on the plane from my day job, I had the oil temperature go off the top of the gauge and hit the peg. Land and shut down, mechanics starting getting nervous because we were way over the over-temp tolerances. The mechanics swapped gauges, cleaned some connectors, did an engine run. They decided it was a gauge problem and sent us on our way with the new gauge. If it can be confirmed a gauge problem, then that's probably great news and go flying.

I'm curious what smarter folks than myself have to say too.
 
My intuition is that it was a bad reading as well - he said he only ran it for about 3 minutes before he saw the temp spike. CHTs and EGTs were in the green.
 
It’s a gauge, no way on a 3 minute run the oil would get that hot. Not sure you could ever get it that hot.
 
Could he have mixed up the CHT with oil temp? If you have a monitor it may have the records. I am not an engine expert in any way but I don’t think the engine would run if the temp was that high.
 
My intuition is that it was a bad reading as well - he said he only ran it for about 3 minutes before he saw the temp spike. CHTs and EGTs were in the green.

Either the probe, the gauge, his eyeballs, or his memory (or some combination thereof) is mistaken. There is no way he forced a 400F oil temperature in 3 minutes. I don't think a full power runup with the cowl plugs in place would get the oil that hot that fast. (The cylinders, OTOH...)
 
I bet the CHT got to 400, not the oil.. as for clearing some fouled plugs, I never had to do more than 10 to 20 seconds to clear it.. if it takes more than that, you should consider something else.
 
In an attempt to clear some fouled plugs, my partner ran the engine in the runup very lean for a while and said he saw the oil temp above 400 degrees before he realized and pulled the power. Engine is an Aerosport IO-360 with dual electronic ignition and automotive BR8EIX plugs.

1) Is an oil temp of 400 degrees even possible without causing a fire? I'd have thought CHTs would have exploded well before oil ever got that hot.
2) What kind of damage could be possible if it did actually hit that temp? The plane is currently grounded at an airport about an hour away from home and I'd like to bring it back where we can work on it, but I'm afraid to hop in without knowing what could have been damaged that may not be caught in a standard runup.

Flash point of motor oil in general is around 350F. Synthetic oil, you can add 100 deg.
 
Agreed with the others - it's possible to hit 400 on CHT in a a few minutes run, but not oil temp.
 
I'll pile on...

If the engine was generating 400F oil temps, it's toast. It would be smoking and likely smell like it had burned. May have even seized after shut down. Something would have had to generate a huge amount of energy. Spun bearing, completely failed bearing, something catastrophic. Pull the blades through, listen and feel. Look at and smell the oil. If nothing noticed, try it again. The engine's got major problems if the temp's legit and running it again isn't going to hurt it any more.

My money would be on indication.
 
Last edited:
Back
Top