TDR Header Blanket Heat Soak Science
 

My Miata has been plagued with heat soak of the IAT sensor causing the car to stall/stumble when coming to a stop. I'm using a GM IAT sensor that is installed directly into a stock airbox, the close proximity to the headers combined with the sensor body being brass leads it to heat soak very badly when idled for extended periods of time. I don't have heat soak problems when the car is consistently moving as the constant stream of incoming air is enough to cool down both airbox and IAT sensor, the readings will still be above ambient but not by a concerning amount (5-20 degrees). But once the car idles for a few minutes, it will heat soak bad enough that the false IAT reading (50-80 degrees above ambient) is enough to make my car run significantly leaner as the ECU thinks that much less air is coming through. This only causes a problem when coming to a stop with overrun fuel cut active, as in any other condition my wideband is able to correct enough to keep things working. When coming to a stop with overrun fuel cut active AND the car heat soaked, it will consistently stumble (drops below target idle rpm enough that I feel the car shaking) and oftentimes outright stall, as the false IAT reading causes the ECU to give the engine less fuel than it needs to run causing it to then stumble and/or stall.

So last week I installed a TDR header blanket to help combat my heat soak issue, and gather some data while I was at it. I knew it wasn't going to 100% fix it, but I knew it would help. So I decided to do an experiment to get some hard numbers on how the header blanket affects heat soak.

The experiment was simple. I measured the temperature of several important parts in the engine bay affected by heat, as well as a few other random things as control group/personal interest.

I measured the temperature of the following:
Header
Airbox
IAT sensor body
the heat shield for my wideband (wires weren't long enough to mount the Spartan controller anywhere else, SO I made a heat shield to help protect it)
Wideband controller
Brake fluid reservoir
Driver and passenger side shock tower (control group)
Engine block
Fuel rail
I also recorded the IAT and AFR reading

The process was to measure the temperature of the listed items to make sure they were at ambient, then start the car and let it idle for 20 minutes with the first 10 minutes having the hood open then closing it. After it idled for 20 minutes, I'd measure the temps again, then I would drive it 10 miles (city driving only), record any stumbles/stalls, and measure temps again, then let it idle again for 10 minutes, then measure temperatures again.

I did the test with no header blanket installed first (ambient temperature was 87 degrees), then let it sit until the next day. The next day I installed the header blanket (ambient was 91 degrees, 4 degrees hotter) and repeated the same process and this is the data I recorded:
https://cimg3.ibsrv.net/gimg/www.mia...c4d318f441.png

I have 3 types of graphs:
1st column of graphs: Shows the measured temperature of each part at each stage of the process (raw data).
2nd column of graphs: Show how much the temperature was above ambient.
3rd column of graphs: Shows how much it heat soaked between each stage.

The data shows quite a bit, but i'm only really concerned with the temp gain after the 10 mile drive (the condition that causes the stumbling/stalling) and it's also kind of a pain in the ass to read. So I made another graph that shows the difference in heat soak with no heat shield compared to with then the header blanket.

https://cimg7.ibsrv.net/gimg/www.mia...86830f8b67.png

The data clearly shows that with the header blanket it heat soaks way less after it idles for 10 minutes. It does also show that it ran hotter overall despite the only 4 degree increase (I blame it on hitting ever single red light on the 2nd drive, and thus idling more than it did the first time).

What's not shown in the graphs is how long it took to fully heat soak (when things stop getting hotter) and how many time it stumbled/stalled. Without the header blanket it took only 4.5 minutes to fully heat soak, but with the header blanket it took almost double the time at 8 minutes to fully heat soak. It also massively improved the stumbling and stalling issue. On the first drive without the header blanket, it stalled 3 times and stumbled 9 times, but on the drive with the header blanket it never stalled and only stumbled twice (despite the higher ambient temp and more idling from being stuck at every red light).

This test is less than perfect, ambient conditions were different, the 10 mile drive while having the same route, had different levels of traffic and I got stuck at every single traffic light on the second run so that ended up being an additional variable. Despite the test being less than perfect, the data and the semi-anecdotal evidence of the car stalling and stumbling less, clearly shows that the TDR heat blanket puts in significant work to help combat IAT heat soak for those who have the IAT sensor in the stock airbox. The other takeaway is that it does reduce overall engine bay temperature which helps with keeping the fuel rail less hot and it keeps more heat out of the brake fluid master cylinder.

TLDR: The TDR header blanket (or really any heat shielding for that matter) makes a very good BANDAID for heat soak as it reduces how badly the engine bay heat soaks and it will greatly increase the time it takes to fully heat soak.