I know there have been a lot of questions regarding the hot air hose and the air box thermostat.

Here's what I did. I bought a indoor/outdoor car digital thermometer from Walmart for $10. Wired the outdoor temp sensor in the air box.

The results of air temp in air box, with the 'offical' air box thermostat wired correctly and in working order (all factory duct work).

(only been testing with ambient temperature ranging from 32 - 50 F)

cold engine (40 amb temp)
after 1 min -idle and 3-4 minutes driving the air box temperature reaches 60F
city driving temp reaches 70-75 F
highway driving temp 60-65 F

Before start up of hot engine air temp is 85-90F (amb temp 50F)
Idling (parking lot driving) 80-85F
City driving 70-75F

Highway driving seems constant at 60F with 34F amb temp

Once it gets really cold, I'll have more results.
(I thought I had a stuck air box valve, but after cleaning (and lubing) off the dust, it works fine)

I think I'll go to Walmart, that's a good idea.

I am surprised at the level of the temp., I thought it would be colder.

I have tested mine by running very cold water on it to close it then let it sit inside at room temp. Mine open before room temp.
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88 765 w/2stage boost & G-valve @ 14 psi

I did not know about this thermostat. Where in the air box is it located? I have an 88 240 DL that is surging and stumbling occasionally and this may be a contributing factor. Thanks for your assistance.

Jim -

The air box holds the air filter. It is mounted on the left end of the radiator, has an air inlet tube towards the front, a large silver pre-heat tube that goes over to the exhaust manifold, and a large short black tube to the Mass Airflow Sensor (MAS), aka Air Mass Meter (AMM).

There is a flap inside the air box that closes off the heated air from the pre-heat tube once ambient temperature is OK. When the thermostat ($35.00) fails the AMM ($100 to 400) gets heated air all the time and eventually fries.

This is a tip that I learned the hard way, and never again. Lack of this knowledged contributes (mightly I'm sure) to the profit of the dealers.

Good Luck,

Bob

:>)

Mine is under the filter in the box
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88 765 w/2stage boost & G-valve @ 14 psi