Thermostat Housing sizes

[340inabbody]

So I am in the process of replacing my intake manifold. I noticed my M1 thermostat housing and thermostat is smaller than my replacement manifold. It’s significantly larger.

M1 hole diameter 1.5” bolt sep 2.8”
New Manifold 2.1” “ 3.25”

What gives? Is the new one set up for Fords or Chevy’s? I can’t buy new thermostat housings based on size but on application. This should be an easy thing but I don’t know what housing I need.

 

[RustyRatRod]

That's pretty interesting. That's slant 6 size. in the Mopar thermostat world, there are two sizes that I am aware of. Slant 6 and everything else.

 

[S'cuder]

Some of the M1 manifolds used a smaller thermostat, maybe the same one as used on Magnum engines.
Your new manifold is probably specced for the one used in V8s from the 1950s until the Magnum came out.

 

[340inabbody]

Some of the M1 manifolds used a smaller thermostat, maybe the same one as used on Magnum engines.
Your new manifold is probably specced for the one used in V8s from the 1950s until the Magnum came out.

Yes I think you’re right. Because when I put my old thermostat housing on the M1, it was too big and I needed to get one for a magnum, so does this mean that the larger one is standard for LA intake size?

 

[townsend]

Chrysler used two different size thermostat housings for V-8 engines , also called water outlet connectors.
The larger size was used thru 1978.
The smaller size was used from 1979 and later.
3698565 - 1978 and earlier
4100490 - 1979 and later
Examples can be found on eBay
Part number search on rockauto shows aftermarket housings.

 

[Professor Fate]

In '78-'79 or so Mopar smallblocks went to a smaller, offset thermostat. Magnum and Chebby size (maybe slant 6 size too? Dunno.).
Most aftermarket manifolds are sized for the earlier thermostats and housings.

 

[340inabbody]

So would a 1970 340 be the right application for this size? Again I have the dimensions but everything is based off application.

Also I noticed that the opening in the manifold does not have any lip. It’s all flat. Is that how the stick manifolds are as well?

 

[townsend]

As was stated earlier, all housings are the same from 78 back. 1970 - 340 housing is correct.
Chrysler #3698565 or Four Seasons #84830.