[Very] Hot Oil in descent

[David Pfeffer]

Flight #2 & 3- working off the sqawks on the PA-30 restoration. As usual, I don't have a "normal" problem. It's always gotta be something difficult to track down...

Problem: Oil temp on the #2 engine spikes to 230 deg F on descent from 4000' MSL once power is retarded and up to 240 deg after landing. Oil remains cool (200 deg F) during climb at 120 mph (cowl flaps open) and cruise (cowl flaps closed). Oil pressure is 70 psi (smack in the green). Single digital CHT on #4 reads 315-320 deg F during descent with high oil temp. Opening cowl flaps and increasing mixture has no effect. Have not had a chance to increase airspeed much because it always occurs descending into the pattern. OAT is 80-85 deg F.

Troubleshooting:
Checked for any airflow obstructions in/around the cylinders and the whole cowling.
Confirmed cylinder baffling is installed properly around cylinders.
Confirmed engine baffling is sealing tightly.
Tested vernatherm. Worked, but had a smiley face on the valve face. Replaced with new (seat looked good).
Fabricated clip to move existing fuel line 3" forward of oil cooler.
Tested accuracy of oil temp sending unit by heating in a pot of oil using a calibrated thermometer.
Tested actual oil temp in sump using 3' thermometer to confirm 225 deg F oil temp after taxi back and shutdown.
Pulled all oil lines (only 1 yr old anyhow) and confirmed no obstructions.
Pulled oil cooler and confirmed no obstructions.
Ran compression test- all at least 72/80.
Oil consumption is fairly low. I don't have an established pattern yet (only flown 3 flights) but it definitely burns no more than 1/4 quart per hour, so I'm assuming no significant blow by.

I'm sending the oil cooler out for overhaul. It's possible there's carbon build up internally, but it has good clean fins. The fact that it only does it when the power's reduced makes me think it's an airflow problem. I noticed there is a 0.25 inch gap between the bottom of the #4 cyl and the oil cooler. Is this by design?? It's on both engines, but would allow air to push below the oil cooler vs. through the cooler. Reduced air pressure due to reduced power may not apply enough cooling flow through the oil cooler. Pictures attached. Both pictures are looking aft from the #4 cylinder. The oil cooler has been removed (hence the big hole in the aft baffle). Can anyone confirm this is the correct baffling for this area between the #4 cyl and cooler?

Other ideas? Engine is 400 SMOH in 2006. If I had bearing going bad, I should really see hot temps all the time, not just descent. I've shot the cylinders with an infrared thermometer immediately after shut down. There's no appreciable difference between them. Could be an internal bearing I suppose, but highly unlikely (I hope!!)

This restoration has been so frustrating...

[N3322G]

Had hot oil temp because the install put a sharp bend in the connection and it got inordinate amount of heat - just one more idea to check.

[David Pfeffer]

Pat,
That's a good call. I don't have any tight bend radii in the oil lines but do have a 90 deg fitting on the bottom line coming out of the oil cooler.

On your next preflight, would you mind checking to see if you have the same gap as in my picture and see if you have straight or 90 deg fittings at the oil cooler?

Thanks!!
David

[N3322G]

David,

I only have a single oil temp probe to the JPI and a single probe to the original Piper gauge. It was the JPI line that had a bad bend at the front end of the engine - used to get 1,340 degree readings on JPI on the ground while the Piper gauge was in a happy range - it was just a bad install.

[md11flyer]

David, I don't think the 1/4 inch gap totally explains the hot oil problem, but that gap is BIG. Do you have that gap on the other engine as well? On both my engines the baffles are tight against the cylinders.
I would guess you indeed have a restriction in the oil cooler but that gap wouldn't help any with forcing air through the cooler. See if you can snug up the baffles against the cylinder.

Gary

[David Pfeffer]

Gary,
Yes- the same gap exists on the L/H engine as well. Doesn't make it correct though. The baffling is tight against the aft end of the #3 cylinder on both engines, but leves that large gap between #4 and the oil cooler on both engines. I'm going to fabricate some aluminum baffling to close the gap, install a new oil cooler and try again. I'm curious to see if anyone else has this same gap though!

[MULEFLY]

In my PA39... took the grandkids up for about 30 minutes a couple of weeks ago... my baffles are pretty tight... I had a hot oil warning display on the JPI on final... but it was >95F that day... usually I don't see it when OAT is 80 to 85. I'd open up the cowl flaps...

Regarding the gap.. ... and I had a bit of a gap on new baffles from Matt Kurke between the oil cooler and the frame. I haven't seen that big of a gap between the baffle and the cylinder... (he has changed the pattern on the ones that he is producing now). I closed it up with a strip of aluminum and then sealed it completely to the oil cooler with RTV.

BTW I also have Hans' plenum on my oil coolers. IF YOUR BAFFLES ARE TIGHT... it helps.. if they are not -- it will not be much help. Baffles! Baffles! Baffles! ... they must be tight!
Jim

[William Flood]

My old Cessna 180 was a PITA in the summer it ran so hot. Same deal 600hrs SMOH etc etc. I tried the cooler, changed the vernatherm, tweaked cowl flaps, tried different power settings, ran her topped up of oil most the time. In the end it turned out my mag timing had slipped and caused most of the issue. I doubt your's is off as you have been very thorough from all I read of your work on this machine.

You could always try Phillips XC oil, and that will drop the temps a bit.

William

[David Pfeffer]

Will, that's not a bad idea to recheck my mag timing. I'll def give it a try. I just got back from vacation. I fabricated more baffling today to close the gap between the number 4 cyl and oil cooler (for both engines), sealed up the baffling more, and installed an overhauled oil cooler. Gonna fly it and see how it does. Will def recheck the mag timing after this next flight.

Thanks!
David

[David Pfeffer]

..oh, and I have been running Philips XC 20W50

[N3322G]

Ran Exxon 20W50 and found higher oil pressures so went back to Aeroshell 15W50 - according to Blackstone it give higher copper levels but I'm happier with the pressures so I stay there as I can fly to any part of the country w/o worrying what oil is in the engines.

[Steve Von Gruben]

Dave, one thing not on your extensive troubleshooting list for the high oil temp is swapping sending wires on the back of the gauge side to side to see if problem follows. A long shot but an easy way to rule out gauge problem.

Steve

[David Pfeffer]

Well, turned out to be an indication problem. Installed an overhauled oil cooler, fabricated new baffling to close the gap between the #4 cyl and oil cooler, and re-flew. No real change, but did perform a number of additional in-air tests.

I can pull the throttles to 15" MP and dive at 180 MPH and watch the RH oil temp gauge skyrocket to 240 deg F. Pull up, add power, and climb (cowl flaps closed) and it drops right back down to 200 deg F within about 15 seconds. I performed a number of other inflight tests as well- getting a goofy response on the gauge with fast descents. I've checked the actual oil temp in the sump after the last 4 flights now and the L/H and R/H engines are within 2 degs of each other every time, despite 60 deg splits in indicated temps. The L/H engine reads very low; R/H engine reads high. I've been busy going through in-air avionics checks and haven't swapped leads at the gauges but I do intend to do so.

Interesting find to share:
Oil temp in the sump reaches 230 deg F after taxi back and shutdown on a 90+ deg Florida day (on both engines consistently). I'm assuming this to be my new normal for such a hot day given both engines are within 2 deg of each other. Sump oil temp is about 210 deg F on an 80 deg day after flying, taxi back and shutdown.

Can the temp indicators be overhauled separately or do I need to pull the whole cluster? I can't recall off the top of my head.

[JIMICS2452]

The indicators can be taken out of the cluster and sent for overhaul. I would also send the temp sensors as a matched set to ensure the sensors are also tested and calibrated to the indicator.

[Charles Schefer]

David,

I had my oil pressures and oil temps overhauled and calibrated like factory new by Air Parts of Lockhaven. They did a great job and I now have solid readings. As part of this process I built test leads to test the calibration of the gauge itself. See my other post here -> (viewtopic.php?f=94&t=7183) for the details.

I can mail you my test leads if you like but it's pretty simple really. The gauge just reads electrical resistance from the oil bulb which is a thermocouple. The readings of 60F / 200F / 260F are based on known resistance levels. My test leads simulate those resistance levels and should cause an accurately calibrated gauge to read those readings. Again read my other post for the details and message me if you want me to lend you the test leads.

As part of recalibrating I had Air Parts test my oil bulbs too and one was bad and the other was OK (for some reason they sent both back red tagged inop but I know they said one was actually OK). I upgraded to newer Rochester bulbs and they calibrated my gauges to those new Rochester bulbs under STC.

This may be OBE by now but my cowls are apart for alternator upgrades so I took some pics for you. Below are pics from above and below the oil cooler of my left engine. There is a small gap between the cooler and #4 cylinder but I'd say its only 1/2 a CM at most. Nothing like 1/4 inch...

Gap from Top View:

Gap from Bottom View:

Best of luck,

- Charles