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Persistent leak at thermostat housing; where the housing meets the head
Topic Started: Jul 16 2012, 07:13 PM (2,629 Views)
jaevans
Elite Member
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Greetings - Well, this is the second time in the last 3 days I've replaced the gasket between the thermostat housing and the head after my head rebuilt job and I am still seeing coolant leaking from the seam. :smackface

First time, I gave a felpro gasket a light coating of RTV on both sides but that leaked. I then cleaned the surfaces again and just used a new cutout of dry felpro gasket material but when I got home from work, it shows that it is leaking again. Am I just not tightening the two bolts enough or do the surfaces have to mate perfectly flat? What do you all use for this gasket? It isn't much of a leak but enough to get the top of the transmission housing wet after a trip.

Thanks,
John
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Memphis metro


Make sure the flange is not cracked or its actually your upper radiator hose clamp needs tightened a little more.
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evmetro


Clean and dry. Rtv and assemble. Wait an hour or two. Fill and drive.
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BigRobRN
Elite Member
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Permatex Ultra black RTV.
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jaevans
Elite Member
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I'm pretty certain that it is the gasket. The upper radiator hose connection is dry as a bone. I wiped everything dry, went for a 10 minute drive and then checked the area. The paper gasket looks as if it has wicked coolant from the inside to the outside in 10 minutes. I'll take it apart this weekend, inspect the housing, clean it good, dry it off and just try a bead of red rtv and report back.
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jaevans
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BigRobRN
Jul 16 2012, 07:53 PM
Permatex Ultra black RTV.
Would the Ultra copper work better?
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Memphis metro


If your using a gasket then the indian head would work fine in my way of thinking.

http://www.autozone.com/autozone/accessories/Fluids-and-Chemicals/Indian-Head-Gasket-Shellac/_/N-25b1
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jaevans
Elite Member
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My plan for this next go around is to just use rtv, either red or ultra copper - no felpro gasket this time. I'll put on the bead then lightly assemble and tighten just until the bead oozes, letting that sit for a few hours before final tightening.
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jaevans
Elite Member
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Maybe I'm using the wrong gasket material - the felpro blue striped gasket material in a roll.
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BigRobRN
Jul 16 2012, 07:53 PM
Permatex Ultra black RTV.

This.

jaevans
Jul 16 2012, 08:03 PM
BigRobRN
Jul 16 2012, 07:53 PM
Permatex Ultra black RTV.
Would the Ultra copper work better?

Same effect.

blue rhino
Jul 16 2012, 08:12 PM
If your using a gasket then the indian head would work fine in my way of thinking.

Or, this.

*****

Fel-Pro P/N 35451 is the correct gasket.

I have installed gaskets on the cooling system, service the system with coolant, and driven away without delay.

My highest degree of suspicion is that the mating flange of the thermostat housing is not level. Find someone with a belt sander. Run the mating flange over the belt sander a couple of times until it becomes level. No need to remove the thermostat and thermostat housing. Blow out the debris and reinstall with a new Fel-Pro gasket and some sort of gasket sealant.


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jaevans
Elite Member
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Hi Glenn, et al.,

Well, my third attempt at replacing the gasket (with the recommended felpro and black ultra rtv) still results in coolant leaking. I did "mill" the face of the thermostat housing on my belt sander before installing again and I got it nice and flat, but "something" is still leaking. After a look at a picture of a head, it looked to me like it may have been the freeze plug as shown in this pic (thanks geoflyer):

head view

A close inspection tonight after my drive home from work shows no visible leaking coolant at the freeze plug (but I am not getting a direct view of the plug), none at the hoses off the thermostat housing, and dampness at the water outlet flange gasket. I think I'll have to take it apart yet again and check the face of the flange on the head for flatness as well while inspecting the hose fittings and sensor fittings to see if it could possibly be leaking somewhere besides the water outlet.

John
Edited by jaevans, Jul 23 2012, 08:12 PM.
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Memphis metro


Take it autozone and aske them to put a pressure tester on the radiator and find the leak.
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sphenicie


are you sure that it is coolant?

could it be oil,,,,,,, drippn down from the distributor base?

you may just focused on the stat housing and overlooking the other source. ? . ? . ?
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sphenicie


top of trans near the clutch actuator arm is common spot for oil to reach, from dist. starts as a little wet spot.
if it shows up in just 10 min, then you could clean the wet spot real good w/ brake cleaner and wrap a rag around the dist and wire it in place good. take it for a runner and see.
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jaevans
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sphenicie
Jul 23 2012, 08:34 PM
top of trans near the clutch actuator arm is common spot for oil to reach, from dist.
Good catch, sphenicie. :thumb There is an oil drop by the bolt under the distributor housing. I'll see about replacing the O ring tonight and check the distributor seal as well. There is, however, still a coolant leak - the reservoir drops about 1/4 inch each day and there is coolant on the block adjacent to the transmission housing. After looking at shots of a block, I was hoping the freeze plug was leaking but there is no evidence of that on mine. Still, the gasket is wet with coolant and I can find no evidence of a leak elsewhere in that area. I'll take it apart again this weekend and check for flatness on both surfaces.
Edited by jaevans, Jul 24 2012, 08:51 AM.
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