[Very] Hot Oil in descent

[Steve Von Gruben]

David, you might want to check your ground strap between engine and mount. You could also fashion a temporary ground lead between engine and firewall and check the one behind the instrument panel. The engine moves around slightly with changing power and airload and could affect a weak ground path. Easy troubleshooting.

Steve

[David Pfeffer]

Good idea too Steve!

[Steven DeGroff]

This is really late but may have relevancy. I had the exact same symptoms in my 400 this summer. The OT guage rarely went beyond the 200 deg ball since major overhaul in 2000 and over 800 hours flight time.

This summer on a three hour flight from Indiana to Outer Banks, NC, I noted the OT creeping up slowly. All else normal. I have a JPI 8-cyl analyzer (EDM700) but without Oil Temp. By end of flight, all was normal but OAT was approx. 250, then on decent, it went OVER 260! That did not make any sense to me.

Troubleshot with mechanic at MQI. (Very helpful and qualified mechanic). Checked baffling, both cooler access, etc. Checked vernatherm. Seat appeared slight worn. Mechanic recommended try new. Overnighted new vernatherm. Test flight-no change.

Called Webco-they said next step flush oil coolers. We questioned this w/ 800 hrs and regular oil changes, etc.

Called Bill Turley at Aircraft Engineering in Bartow FL. I consider Bill one of the best Comanche guys there is. He did my pre-purchase inspection in 1997 and my first annual. I would still use him for my annuals if he was closer to Indiana or if I had more free time to vacation in Florida, but I don't so I occasionally pester him for a question like this.

Bill said it sounded like an indicator problem. He said it doesn't make sense but it seems there's a resistance change due to old instrument and something changing in the conditions during descent. May be a vibration change not present in climb and cruise. He saw the same symptoms before.

We had JPI overnight a probe so we could get a digital read-out on my EDM 700. I should have done that when I added the EDM 700 at overhaul. Anyway, new digital OT readout showed about 200-220 all day long on the EDM 700. Problem solved. Old Guage out for o/h.

[N3322G]

Steven,

Very interesting. Thanks for sharing.