Quote:
Originally Posted by Ecky
Just came across this thread, and unfortunately I'm coming into summer, so it isn't a whole lot of immediate use, but I do have a few thoughts to add:
It might be worth exposing an airflow path around the coil packs. These are probably pretty heat resistant, but being excessively warm might reduce their lifespan.
The results speak for themselves, but I have some skepticism about the mechanism by which it's believed to work. An insulated ceiling does virtually nothing if the windows are open, so to speak, and I wonder if the added insulation between engine and hood isn't instead functioning mostly to fill space that air would otherwise be flowing through, rather than actually insulating a heat loss path through the hood.
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Hey Ecky!
I first installed the insulation during the summer and have mostly used it in warmer weather. It basically shortened the initial warmup of the vehicle by 45s+ish, and helped it retain heat. So it improved fuel economy by a small amount, especially on short frequent trips. I actually haven't had an opportunity yet to test it in the cold, where it seems like it would perform best, so I'm very interested in hayden55 and Phase's results.
Your skepticism seems unwarranted. By your same logic, insulating an attic in a house would have virtually no benefit because of heat loss through the sides. But if you've ever insulated an attic, the difference is night and day throughout the whole house. Furthermore, even if we accepted your premise of an infinite side heat sink, there is a header gap between the ceiling and the top of the windows. The temperature there would definitely change, at the very least into a gradient.
However, if we restrict ourselves to just observable facts without hypothesis bias, I removed my insulation first because I was intending to put a bonnet vent in. That caused a) my warmup time to increase by 90s+, b) the hood to become so hot I couldn't touch it after driving, c) my fuel economy to go down, and d) my engine temp to waver constantly between 175F and 185F (operating range is 185-190). After installing the insulation, the warmup time decreased, I can touch the hood fine, my mpg went up, and the engine temps were good again. (Right now they are wonky because I've messed with the radiator inlet. That's a separate issue that occurred months after.)
Anyhoo, you may draw your own conclusions from that data. The one that I've drawn is that the hot hood with air flowing over it acts like a secondary radiator, with a significant heat flux through it. Cheers.