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Discussion Starter #1
I have done the thermostat gasket 4 times. I have gotten a new housing, various brands of gaskets, a new thermostat, and blue RTV on both sides every time. I have followed the instructions for the RTV drying times exactly, keeping it completely dry while drying. I have cleaned he mounting surface on the intake manifold with wire wheels, steel wool, razor blades, scrapers, brake clean, ect. This time I thought I finally got it because it hasn't leaked a drop in 5 days. Today was the first 80 degree day of spring and i went from 0 to 50 without really letting it warm up. When I got home I found it was leaking again, and sprayed all over the engine bay like usual. The temp gauge has always got to about 200 on warm-up then dropped and stayed at about 150, even before the leak. I really don't want to put stop leak in there but I'm getting desperate. Any ideas what could be going wrong?
 

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Where does it say anywhere that you need to use RTV? The Mopar thermostat comes with the seal and that is what I always use dry with no RTV. In my experience, coolant and RTV don't mix.
Back in the 80's when RTV first became common in automotive engines, the instructions were to apply it and torque it down as quickly as possible before it even begins to skin. That has never let me down. I don't know why the tubes say to let it start to set before assembling.



 

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Discussion Starter #3
I used RTV on both sides of the paper gasket that seals the housing to the intake. Sorry I should have mentioned this is a Dodge 5.2. I did try to do my research and from what I've seen, the thermostat itself doesn't have a gasket, it sits so it is flush with the manifold surface. The first time I tried it, I used just a gasket and got a persistent leak
 

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Assuming you are referring to the Dakota in your screen name, I am not familiar with the '99 5.2. The Mopar thermostats I have seen have a thick o-ring type seal that compresses and seals. If the aluminum mating surface of your intake manifold is corroded and pitted, that could be the problem. See if you can get it machined flat and clean. If you insist on using RTV, forget the paper gasket. Apply a thin 1/8 inch bead to dry clean surfaces and immediately assemble and torque the bolts with a torque wrench. Wait a few hours minimum (overnight would be even better) before refilling the coolant.



 

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the "5.2" (I prefer "318 cu.in".) has a paper gasket not an Oring. I do agree that the manifold flange may be pitted (cant see it from here) but the T stat fits in a recess within the manifold then the gasket above that and then the water outlet and bolts. I have had to replace the water outlet housing a time or 2 for a chronic leaker before. pretty simple arrangement though on the Magnums (any 318 '92 and newer) they tend to be a little more buried than the older versions. Check the temp sending unit to the pass side of the T stat, neat where the heater hose connection to the intake is. They get brittle and break easily where the plastic part is crimped to the brass base/screw in fitting portion. I just did replace all belts, hoses and thermostat on my most recent addition to my "fleet" a '92 version of your truck (virtually identical engine) and had to replace that temp sending unit along with the other parts mentioned, it is about a $14 part.
I also had an issue with my Durango thermostat leaking, turns out I pulled the threads as I unscrewed the bolts that hold the water outlet/Thermostat in place??? as a quick fix at that time I just tapped the hole in the intake to the next larger size (3/8-16 NC) but have since redone it and Heli coiled both thermostat bolt holes back to the standard 5/16-18 thread size.
 

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Discussion Starter #8
I will replace the temp sending unit next. Would that have anything to do with the temp gauge fluctuating between about 180 and 230? Bad sending unit? I have "burped" the radiator a few times but there still might be an air pocket in the upper hose or the area under the sending unit. Or could the leak be creating an air pocket?
 

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The leak is most likely creating an air pocket.

Looking at the pics at RockAuto, it looks like your thermostat housing attaches mechanically like the one on my 1988 does; the factory design leaked every time I put it on, so I ordered a replacement that was a single casting (instead of a stamping where it bolted to the intake).

That might be worth doing also.

RwP
 

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Coolant issues are such a pain in the balls. My 06 Dakota went through two Water pumps in 2 years and I have no idea why!
IDK how many miles you put onto that truck between water pump changeouts but in this day and age my #1 suspect would be the quality of the parts you bought.... just because it was a well known, old name brand, with all of the outsourcing that happens you really have no idea what you bought...
I once had an 89 Diplomat ex police car. I replaced the WP with a reman, a Cardone branded product. That WP lasted a WHOLE 200 MILES! and I had to re do it because it leaked like a sieve out the weep hole. I took it back and went with a brand new one instead (not much difference in price either) and never had a problem with that again, we had that car for many years.
 

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Check to see if the two bolts on the housing are the same size. One is supposed to be shorter and one is supposed to be longer. I can't remember which one is supposed to be where, I think the shorter in the front but thats not hard to figure out. Just went through this issue last week
 

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Check to see if the two bolts on the housing are the same size. One is supposed to be shorter and one is supposed to be longer. I can't remember which one is supposed to be where, I think the shorter in the front but thats not hard to figure out. Just went through this issue last week
Both my bolts are the same length stainless steel replacements. No leaks ever. Also, this post is well over a year old.
 
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