Wacky oil temp issue.

dhall_polo · #1 07-09-2010, 06:44 PM

In over 150 hours of flight, I've experienced nothing but rock solid temps in good ranges on all probes. I've flown in cold and hot/humid conditions with no problems. With normal settings the oil temp is typically parked in the high 180's, and the CHT's are easily maintained in the 350 range.

The other day, I experienced a condition of climbing oil temp. They climbed into the red and kept going. Changing power settings had no effect. Lowering the nose provided temp relief, but not much and the temps still climbed. At the same time, the CHT's were solid green. Lowering my power setting did result in lowering CHT's, even as oil temp climbed.

After a normal landing, I inspected the cowl. No clues. The temp probe and wiring all look fine, nothing loose. The oil level was exactly where I expected, just above 6qts and still honey colored from the last oil change around 6 hours and 3-4 flights ago.

Ideas?

scard · #2 07-09-2010, 06:57 PM

I had a similar issue early on (first 100-200 hrs). GRT oil temp sensor change fixed it. It sure gets your heart pumping doesn't it?

.

Brantel · #3 07-09-2010, 06:58 PM

Confirm the temp probe is accurate. Might be a bad ground or bad probe.

Heat up some oil with a known good thermometer and check it out before going off on what might be a wild goose chase...

nucleus · #4 07-09-2010, 08:24 PM

Call Sandy at GRT and get a new sensor, I had one that would suddenly drop.

Hans

kevinh · #5 07-09-2010, 09:03 PM

yep - Same thing happened to me (on my first flight! - after testing successfully on the ground). A sensor swap fixed it. Lower the sensor into some boiling water and see if it reads 212 deg.

Andy Hill · #6 07-11-2010, 01:42 AM

Going back to the flight which must have given you some concern... a significantly rising Oil T which was genuine I am fairly sure would see the Oil P falling to a degree. Am sure someone can confirm/deny/add some figures... which would be of interest to us all.

As an aside, we had an intermittant fluctuating Oil T issue - clearly a sensor / earth issue. It was a Dynon single wire sensor. In flight diagnosis later tried turning off the Alternator (temporarily) which "solved" the issue... and hence confirming the "earth" issue. All checked out, and easiest solution was to replace sensor with a 2 wire one.

Andy
RV-8 G-HILZ

Scott Hersha · #7 07-11-2010, 07:17 AM

I had a similar situation to Andy's with fluctuating oil temperature indictions. I have the same Dynon single wire probe where it grounds through the mount and therefore the engine ground strap. These things work on very small voltages, so a really solid ground is a must. I changed my engine ground wire and where it's connected to the engine and the problem was solved. The two wire probes are less problematic - and more expensive (of course).

dhall_polo · #8 07-11-2010, 08:12 PM

I went flying today and oil temps were perfect. Gotta love intermittent problems. I've been advised offline that one possibility is a sticking vern-a-therm.
http://www.avweb.com/news/maint/182617-1.html?type=pf

Oil temp probes are cheap, so I'm going to get a new one and take that out of the equation. I'll also pull the vern-a-therm and clean/inspect the thing. Naturally, it's not in a great spot to get a wrench or socket on the thing.

Thanks for the replies. I'll post back to the list if/when I'm sure what the solution was.