Replaced thermostat and gasket earlier today with a new blue felpro gasket. Cleaned up mating, surfaces, torqued to spec, put it all back together, and... leak. It's leaking towards the back bolt. Don't want to over-tighten and strip it. Anyone else here that's done this, did you use any sort of sealant? Thanks!

 

I usually put some sealant on them. My personal favorite for that application is Permatex Aviation Form-A-Gasket, but I'm sure there are others that work just as well. I wouldn't use silicone with gaskets, though.

 

Yep, Permatex sells a small tube of sealant designed to be used for water pumps and thermostat housings; I ALWAYS put some on both sides of the gasket.

RwP

 

Yeah looks like I'm gonna have to redo it. I tried readjusting, making sure there was even pressure on each side, tightening it a bit more and it's still has a significant leak. I'll have to pick some of the permatex up and try again. Thanks fellas.

 

When you take the housing off to redo it look for cracks. The permatex should seal any small ones. I have a roll of gasket materiel and use it like Ralph says permatex on both sides (lightly but full coverage all the way around the bolt holes not just the outer perimeter).

 

Actually I have never had the t-stat out of my dodge. But on other cars that I have done, the thermostat sits in a slightly indented area. It it is out of this area, it will leak. Hope this makes sense.

Here is a picture of a housing with the groove. Sometimes its in the engine.

http://www.bing.com/images/search?q=...6o0&ajaxhist=0

 

Went out this morning and picked up some Permatex. Cleaned everything up again, coated both sides of the new gasket, tightened by hand and let it sit for an hour. Then came back and torqued the bolts down.Tube says to let cure for 24 hours before refilling and firing the engine up so I will. The reason for replacing is my engine not getting up to temp. I bought a service manual and even though it says not to replace unless a #17 trouble code is thrown, I really can't think of what else would cause the issue. My temp gauge goes about 1/4 of the way up after running the truck for a while but doesn't throw a code. Poor heater performance too, but gets hotter when revving the engine up.

 

Possibly a bad water pump?

Also, try flushing the heater core.

I had to replace the housing on my 3.9 LA; I can't find the new one I used, it's a casting and has 3/8" to 1/2" thick ears.

RwP

 

Water pump was apparently replaced by previous owner right before I purchased, and I believe this because taking a look I could see ugly red RTV squeezed out all around the housing. Also read that these heater cores are prone to clogging, but once it gets up to temp both hoses are equally hot. Someone replaced one of the original black hoses with a red one so thinking they may have tried flushing it in the past. I figured I'd start with the thermostat and go from there. Not too optimistic though as I removed the old one which didn't appear to be stuck open, and after putting it in a pot of hot water, seemed to be operating correctly. Beyond that I thought maybe the housing wasn't sealed well and coolant was sneaking through around it? Once I get a chance to fill it back up I'll make sure to thoroughly bleed it.

 

Well, one last thing.

Remove the fan temporarily and see if it heats up enough.

Clutch may have failed, causing it to over-cool.

(You can also see if you can spin the blades when it's all cold; if you can't, then the fan has seized. I'm not sure how much drag IS OK; I just did the front seal on my timing chain cover and while doing that swapped to a new clutch, and it's a LOT looser than my old clutch was.)

RwP