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Hot topic question


Well Known Member
Okay here’s a question for the brain trust of Vans Air Force. I was wondering just how hot it gets in the cowl behind the baffle walls in the unpressurized portion of the engine area? I was looking for wire supports for my Slick magneto wires and I couldn’t find anything that fits. Lots of harness supports out there but they’re for the automotive market and too big. I made my own supports out of Delrin to organize and support my harness. After I was finished and installed them, I asked myself if there was a chance of melting or deformity could occur. I did a google search on the melting point of Delrin and it’s about 374 degrees F. So I put a few Delrin offcuts in a toaster oven and it does seem to melt around 350 degrees (the round dial temperature control is probably not that accurate). In my google search, I learned that Delrin is a thermoplastic which means it will melt at a given temperature. Materials like Vespal or Torlon are Thermoset plastic meaning that it will not melt. Plastics like these two would be perfect but unfortunately are prohibitively expensive. So I’m just wondering if my Delrin wire supports will survive the harsh environment inside the cowl? Has anybody worked with another type of plastic, I am not aware of. Thanking everyone in advance. Like I said, a hot topic.
John Van Lieshout
RV6A QB 88%
AeroSport Power IO-375 195hp


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Not a problem. Air temperatures in the accessory case region rarely exceed 200F in flight for anyone. It may go a bit higher given a hot shutdown, but nowhere near 300, and it doesn't last long.

The big player is radiant heating, not convective, in proximity to exhaust headpipes.
My older VM1000C had an extra probe for carb temp. Since I’m fuel injected I had no use for a carb temp gage. I renamed it Cowl Air Temperature and placed it near the engine driven fuel pump. The temperature ranged 60-65 deg C.
Data from self-adhesive temperature strips

Others have weighed in but here's some data to bolster that - I have these handy temp strips (from McMaster Carr) on my P-mags; as you can see this one never got above 210 in the several hundred hrs. that it was on there.

BTW P-mags have a recommended 200F temp. limit and they're designed to go in the same space. So yeah, you're good.


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