I have a 66 f100 4x4 with a 390FE. The thermostat housing on the truck is much smaller than the opening in the intake manifold. I have to RTV the thermostat to the housing and let it set up before installing. When I buy a thermostat for the truck, the thermostat the store sells me fits the housing, not the manifold.

Are there manifolds with different sized openings for the thermostat?

 

Yes, there are differant size housings. The older engines used the larger stat, but I don't remenber what year that this changed. Find the one that fits the manifold and get the stat that fits them.

 

head to a junk yard the correct one is larger on the hose end as well. It angles off the intake toward radiator as well rather than a 90º/... note: this may play havic with the radiator/hose (unless using a hose adapter already)

66bertha: 1968

another option would be to use sheetmetal or ? to make a shim/trap to hold the smaller stat in place.

 

1965 to 1967
T-stat flange diameter 2.49"
T-stat gasket hole 2 1/4"
Gates gasket # 33625
T-stat housing takes a 2" hose


1968 to 1976
T-stat flange diameter 2 1/8"
T-stat gasket hole 1 13/16"
Gates gasket # 33637
T-stat housing takes a 1 3/4" hose.


1965 to 1967 had 2" I.D. hoses top and bottom.
The Automatics had a pipe and 2" I.D. hoses on the bottom.


1968 to 1976 had 1 3/4" I.D. top or (1 3/4" I.D. to 2" I.D. at radiator)
The bottom hoses were 2"
4" thick radiators used a different part # for the bottom hoses than the thinner radiators.

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This is from the gates website. (above stuff).
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I just put a 1976 4V intake on a 65 352.

My original radiator had 1 2" inlet, my original T-stat housing had a 2" outlet.

The 76 4V intake has the small housing (1 3/4' hose) and angles to the left.
My newer radiator has a small inlet also (1 3/4" hose).

I found a molded gates hose, (# 21034 )it has an angle in to match the t-stat housings angle.
It has a 1 3/4" I.D. at the t-stat housing and 2" I.D. at the radiator.

The problem is the radiator side is 2" I.D. on the hose.
...but it looks like the radiator side might be to long and I can cut 2" part off the the 1 3/4" size.

I havent had the hose under the hood yet.
Sorry this is so long winded.............

Regards.


Richard.