Quote:
Originally Posted by Talos Woten
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.
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What got me thinking along these lines was the experience of living in a very leaky house in winter. I heavily insulated the attic, and under the floor, and it would still lose all of its heat in
minutes rather than hours, especially if the wind was blowing, because all of the seams around the windows and doors had high levels of convection cooling. Until I went around and caulked all of the seams, that insulation was next to useless.
Taken as a logical extreme, you can place a double paned window on the ground near a camp fire, and it'll keep you warmer, but only because it's a wind break. The replacement rate for all the air in the engine bay is just fractions of a second if the vehicle is moving even at walking pace.
Quote:
Originally Posted by Talos Woten
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.)
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I agree 100%. Whatever the reason, it works.
Quote:
Originally Posted by Talos Woten
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.
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On my car, even after driving for hours, the hood is not discernably warmer than ambient. I'd wager that insulating my hood would make little difference in terms of heat loss through it until I close up the engine bay and keep fresh air out adequately for the hood to get warm. It stands to reason that you engine bay already has its airflow limited enough.