dhall_polo

dhall_polo

Well Known Member
I experienced a strange pattern with oil temps. It's actually resolved now, but I thought I'd share and see what the list comes up with for ideas or trouble-shooting. I'll post the fix in a bit.
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Preface.
My RV-7 has under 200hrs. Up until fairly recently, all temps have been perfect, and she's been tested in cold and hot to very hot weather. She routinely cruises with CHT's in mid 300's and oil temp stuck on 187F. Then a negative pattern developed. At first it was very intermittent, but over time it became predictable:

-Within 20 minutes of takeoff, Oil Temps reach the warning mark. They keep climbing a degree every few seconds.
- CHT's and EGT's are good.
- Nothing slows the climbing oil temps. Lowering the power setting - nothing. Nosing over - nothing. Cycling the prop might get a little reaction, but nothing lasting.
- All the while, CHT's and EGT's remain good. The oil temp keeps climbing.

Once this happens, I land, stop, and immediately restart the engine.
- The oil temps quickly shows a reduction of 20-30F.
- No further issues on that flight. Temps eventually lower and stay stuck on 187F again.
- If I fly again that day with a short break - still good.
- Next day: rinse repeat this entire pattern.

Hint: It ain't the temp probe. I replaced that to no avail.
 
Vernatherm would be my best guess too.

Second guess: FOD in an oil cooler hose.

Third guess: Wiring issue, such as a partially seated pin on a d-sub connector.
 
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I like this

Too many times we have problems cited with many potential solutions, only to find that we never know how they resolved.
It would be nice to her how this one ends.

My bet is vernatherm as well.
 
My thought process is largely a function of the CHT remaining stable. I am assuming that the oil temp did not actually rise otherwise the CHT would have. Hence it is a connection, sensor type issue.

If my oil temp/CHT correlation is wrong then this is idle rambling.
 
Wild guess - Oil pressure related

Sounds oil pressure related since from a cold start on the initial run of the day the oil pressure will be higher until warmed up. The high pressure must be blocking something. Then when you stop your engine the oil pressure drops and "resets" whatever the problem is. Then on subsequent flights with the warm oil the oil pressure is less than what is was when the engine was cold and doesn't cause the blocking.:confused:
 
Vernatherm!

OK, you guys are pretty smart. I had never heard of a vernatherm before, and now I'll never forget it. I posted on this general issue several months ago, and most of the replies were suspecting an oil temp probe issue. The pattern wasn't as developed then, so the probe was a decent guess.

Credit to Kahuna, who suspected vernatherm the first time I experienced the problem. I went the route of replacing cheap stuff first, so I replaced the temp probe. Now I have two perfectly good temp probes. A new vernatherm goes for just shy of $300 smackeroos.

After removal, the old vernatherm seemed to stick or click a little when I rotated around with my hand, whereas the new one did not. I haven't disassembled it yet, but I will. I tested it in boiling water and it basically worked, maybe expanding a little after the 185F rating. No conclusive failure there, but the sticking could explain my issues.

The new vernatherm is in, and I'm back to having perfect oil temps again for the last several flights. I think it's safe to say - solved!
 
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