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post #1 of (permalink) Old 11-11-2002, 02:59 PM
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T-stat housing gasket leaking after changingT-stat

So, my radiator on my 88 had seen much better days, lots of pinholes, rotting cores, etc. I bought an upgraded 3-row radiator and figured I'd do the job right and get new hoses and thermostat while I was at it.

Well, got it all back together and used a thin layer of RTV Blue on both sides of the thermostat housing gasket and it was weeping when I filled the system back up :-(

Yes, I did clean the head and cover mating surfaces well, got rid off all the old gasket and corrosion. I even used brake cleaner to remove all traces oil oil, coolant, etc from the metal surfaces before putting it together.

It was leaking from near the bottom bolt the best I could tell.

Is there some secret?

Use gobs of RTV(seems like a bad idea and good way to get a lump lodged in a coolant passage somewhere)?

Do I need to cover the threads of the bolts with RTV? I did NOT do that, although I think we may have done that when I did the water pump on my 300ZX.

Off to the parts store to get a new gasket now......


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post #2 of (permalink) Old 11-11-2002, 03:38 PM
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Re: T-stat housing gasket leaking after changingT-stat

1. Remove the housing.
2. Clean both block and housing surfaces.
3. Inspect surfaces or gouges.
4. Put the Permatex Blue (is that what you used?) on the block side of the gasket.
5. Put the Permatex Blue on the Housing.
6. Let them skin for about 5 minutes.
7. Mate the housing and gasket.
8. Mate the housing/gasket to the block.
9. Make sure the Thermostat is not lifted.
10. If you have sealant all around the bolt holes shouldn't be necessary to put sealant on the bolt threads.
11. But, it's not going to hurt.
12. Make sure you're not over torquing the bolts.
13. Let set for 1/2 hour before starting the engine.
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post #3 of (permalink) Old 11-11-2002, 03:49 PM
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Blue Permatex


Yes, it was the Blue Permatex for water pumps, same tube I used on the Z which didn't leak.

I put a thin layer on both sides of the gasket per the crappy Haynes manual.

I'll use the nipple on the tube to make a raised "trail" of sealant around the pieces this time.

I let the sealant set up for almost 4 hours before filling the engine, and I left the top hose off the housing so the RTV could breathe as it cured.

I ensured the thermostat was seated correctly on installation. I also drilled a small hole through the flange to aid in expelling air in the system as it was filled, per a post I found using search on the site before starting the job.

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post #4 of (permalink) Old 11-12-2002, 02:07 PM
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Thanks Leve,


Just wanted to say thanks for the info, and it seems to have worked.

Not sure if I had not put on enough silicone, or if the thermostat had dropped slightly or what. I just cut a new gasket out of the roll of material I bought to make one of my venturi gaskets that didn't come with my carb rebuild kit.

I have let the engine come up to temp(stays at the mark below 210) and it seems to be OK. I let it run for about 10 mins, top of radiator is too hot to touch, but bottom stays cool, and heat comes out of the heater.

Anything special I need to do to "bleed" the system of air? I did drill the small hole in the thermostat to let the air out as I filled the system, and I have the coolant resevoir topped up so it can suck coolant back in rather than air after it cools down.


post #5 of (permalink) Old 11-12-2002, 02:18 PM
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You are Welcome!

Glad it's working. Just make sure the heater is working and coolant is circulating through it by turning on the heater controls. That little burp hole in the thremostat rim should take care of any trapped air behind the thremostat.
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