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Discussion Starter #1 (Edited)
I have a 1985 Ramcharger with the 5.9L 360.

I just put in a new alum radiator and milodon high flow water pump.
I now have in my possession both of the high flow thermostats that milodon makes, neither of which fit my intake manifold. Now comes the question

The smallest of the two fits the recess in the water neck. Here are some measurements I made.

Thermostat sleeve Dia: 1.563"
Dia of shoulder on thermostat lip: 1.824"

Manifold Hole Dia: 1.546


It appears that by the way the thermo operates i need to get the manifold hole out to the dia of the shoulder. From what I can tell there is plenty of meat around the area that i'm not going to be weakening anything too much.

Is this ok to do? I'm planning on just taking a dremel to it and working it larger till it fits.

Thanks

Gavin
 

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If the thermostat doesn't fit, it's the wrong thermostat. I wouldn't modify the manifold for what is probably the result of a catalog error. There are two thermostats used in Mopar engines, the manifold hole stays the same and the removable housing/water neck changes. The early one fits '78 and earlier and the new style fits '79 and newer.
 

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Discussion Starter #3 (Edited)
I have the MIL-16401 and MIL-16406. I called Milodon directly and they confirmed that these are the only two thermostat sizes they have. I also have a Mr Gasket therm #4364 which appears to be the same part as the MIL-16401. I also got a replacement water neck that is cast instead of the stock stamped(?) piece that was getting eaten away.

As is clear and conveyed to me by the guy at Milodon the difference between the 16401 and 16406 is the size, the former being the smallest. It only doesn't fit by a fraction and the guy seemed confident (seemed like an older guy that knew his stuff) that the smaller would fit. So I'm wondering if i didn't just end up getting a manifold than was poorly machined from the factory. Which wouldn't surprise me.
 

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The stamped steel neck is the '79 and up version. The cast model is the '78 and older version. You shouldn't swap them but it's not uncommon for aftermarket performance manifolds to use the early version even if the manifold you took off use the later one. The difference is the bolt pattern and the diameter of the thermostat. What exactly is the manifold you are using? Is it a new manifold that you just bought? It's possible it was machined wrong, but if it worked previously, it should still be the same now.
 

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Discussion Starter #5
The manifold is stock, same one that's been on it (as far as i know) since the day it was built. The thermostat i took out looked like it might have been the original as well. The normal (non high flow) therm I took out doesn't have any where near the tolerance required by the high flow it fits in the hole real nice.

Thanks for your help with this. It just seems like this truck is the oddball for parts.
 

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Looking at the thermostat, I think the outer ring opens instead of the center plate like on the original. I would open up the manifold just slightly larger than the sleeve part, like halfway between the sleeve o.d. and the diameter of the lip. You don't want it to fall into the manifold! This is a different type of thermostat, so some modifications may be necessary. Do it and don't look back.
Travis..
 

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Discussion Starter #7
I think I was looking for one redneck SOB to tell me "go for it" and I think you might be that one Travis. Now all i need is a 100' extension cord to reach the dremel out to my truck.

I think I have to get out just past the shoulder though. Otherwise I don't think it will sit in there properly under the water neck.
 

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According to the Milodon website, the 16401 isn't for a Mopar. It's for "180° Thermostat - Chevy (All) and Ford (All except pre '67, 390-428)" -per the website. The two that are supposed to fit Mopar applications are 16405 (160°)and 16406(180°). I'd say their thermostats are made a little off. I can check my catalogs, but I don't a Mopar and Ford thermostat are the same.
 

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Discussion Starter #9
the 406 is listed as "All Chrysler" but after it didn't fit I called Milodon directly (Awesome that some places still have phone numbers) and the guy said that the catalog descriptions loose their meaning after mid-late 70s and once your in the 80s it's a crap shoot for which size fits.
 

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Honestly, I think I would sent it back and tell them no thanks. If they can't keep tract of what fits what, who needs them? It's not uncommon with Mopars since they are the underdog and don't get the sales numbers the GM crap does. A high quality stock thermostat flows plenty to keep up with the flow of any water pump. I never had any issues with the high flow performance pumps from Mopar or the Flowcooler pump I had on my drag car. Remember the whole point of a thermostat is to restrict flow to regulate temperature.

Also the website says the 16406 is: 180° Thermostat - Chrysler (All) and Ford 390-428 (pre '67)

http://www.milodon.com/water-pumps/water-pumps.asp
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Discussion Starter #11
OK so assuming I'm going through with this.

Should I "machine" the full depth out to fit the ring, and then just a recess for the lip? Or just go all the way through to fit the lip and the ring?
 

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The manifold is flat and the recess for the thermostat is in the neck right? It's been a while since I've had one apart. If in fact this is the case, I'd open up the hole in the manifold and put it together.
Travis..
 

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Discussion Starter #13
Well, I did it, it only too a little shaving to get the thing to fit in there so I'm going to guess it was a defect.

thanks for your help
 
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