O-290-D2/MA-3SPA Dies when heat soaked

[snopercod]

I made a short trip yesterday and when starting up for the return trip, the lower cowling temperature was up to 180F. The engine didn't hesitate or die on me so maybe the additional air to the oil cooler helped? Time will tell.

[snopercod]

I finally got around to checking the calibration of my Rochester oil temp gauge/sender. I heated up some water in the microwave and dipped both the sender and my Fluke thermocouple in the hot water. The gauge read right on between 180F and 200F. I also used a 39 ohm resistor to simulate 245 degrees and that was right on as well. I'm calling it good.

Yesterday I made a flight to Elizabethton, TN [0A9] and the OAT on the ramp was 30C. The plane sat there for three hours in the hot sun and I had no problem with the engine dying on me as I taxied for takeoff. So I'm becoming more convinced that the carb was getting heat soaked by the oil sump and the additional air to my oil cooler has at least helped, if not fixed the problem. During my condition inspection next month, for good measure, I'm planning to add a 1/16" phenolic spacer and two gaskets between the sump and the carb.

Also, I bought a $16 digital temp gauge on Amazon and intend to install the probe in the carburetor so I will know for sure what's going on in there.

[snopercod]

I'm calling this problem solved. Today I was stuck in a line for 20 minutes waiting to take off with no problems at all. OAT was 90F and lower cowling temp got up to 180F. While waiting, I was idling at a normal 1100 RPM with the mixture leaned and not so much as a hicup. I left the boost pump off. I can't point to one single thing that solved the problem but I believe it was NOT vapor lock but, rather, the carburetor being heat-soaked by the oil sump. Here's the list of what I did:

1. Added more cooling air to the oil cooler
2. Added a 1/16" phenolic thermal isolator gasket between the carb and the oil pan.
3. Replaced the fuel line from the mechanical fuel pump to the carburetor to remove all 90 degree bends and stay well away from the oil sump and exhaust system.
4. Added a carburetor temperature gauge so I could see what was going on in the carb.

My carburetor temperature was 20C after startup, 45C during the long wait, 20C during climbout, 16C at idle power during descent, and a whopping 65C after landing and shutdown. Q.E.D.

[Tommycat]

Man, glad to let that one out!

Well done Snopercod!



I foresee a scat tube dampurr in your future...



Best regards,

[snopercod]

Originally Posted by Tommycat

I foresee a scat tube dampurr in your future...

LOL! about the cat photo. Too funny. Yes, I've already noticed that the rear two CHTs are running 20F hotter than the front two (but still well below 400F), so partially blocking off those holes in the rear baffles would make sense when not needed. Maybe I could lash together a thermostatically-controlled damper? (Just what I need, another project.) Thanks for the laugh.

[snopercod]

Another date point: Today I was waiting at the hold short line for about 15 minutes on a hot day. My carb temp crept up to 40C so I increased my idle speed to 1700 rpm and the carb temp quickly dropped back down to 29C. I have to believe that the extra fuel being vaporized was cooling things off. Regardless, my engine didn't cough and sputter when I started my takeoff roll so I pretty much have this problem licked.