DanH said:
I realize this is a discussion of the cure, but I'd like to hear more about the problem.
What seems to be the major heat source, radiant heat from the exhausts or conductive from the engine case? Are there other factors
Cannot answer this, I'd be lying if I told someone this or that caused the problem, to many parts with different temps, Cylinders, heads, exhaust, oil, airflow needs, etc.
Alan, can you tell us a little more about your actual temperature measurements? What sort of pump temp is typical in flight (unshielded) vs following a parked heat soak session?
This question cannot be answered completely because of so many reasons,,,,,, Ambient temps outside, cold AVgas versus sunbaked fuel in the tanks sitting in the sun, the color of you wings, black or dark painted wings on top will have higher fuel temps, engine configuration and cooling airflow needs at the back of the engine around the accessory case / fuel pump, fuel line material, insulated or bare, parking into the wind or out of the wind, not one RV is the same. If conditions are right and you live in the south or someplace where it is HOT, vapor lock can happen as I've seen it on mine one time, and a couple of my friends RVs with injected engines have also vapor locked. The perfect condition for vapor lock is with hot fuel in the tanks from sunbathing, landing the airplane in 100F+++ air, shutting the engine down and letting the engine heat soak for a few minutes, start the engine then take off without a boost pump (injected engines) and spitter spatter the engine starts to run rough, slow down or die. As for temp reductions, I've seen as much as 50F temp reductions at the fuel pump with blast tube and properly designed cooling shroud installed on takeoff. Actual temp of the fuel pump housing at the case? Depends on CHT's, EGT's and oil temps, etc..... You run a hot engine, you run hot fuel pump / AVgas temps. No I did not put a temp probe in the fuel line itself, I used a probe attached to the fuel pump housing, maybe not the best way to test it, but it seemed effective and the probe was not in the airstream of the cooling shroud air. From what feedback I've had and personal emails I don't think it is cost effective for me to make custom fuel pump cooling shrouds at this moment. I had plans to build a very nice cooling shroud to sell, but when others are making them for $60 or so, I'd be loosing my butt with the shroud I designed. So if anyone is interested go buy one of the cheaps ones listed in an earlier thread on this link. Sorry I didn't answer all the questions but I am a firm believer in keeping the fuel cool for safety reasons and horsepower gains.