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Discussion Starter · #1 ·
I have a 2000 gmc Sonoma 4.3l v6 and I just changed the water pump, thermostat, thermostat housing etc, got everything out back together and started to add coolant and it’s leaking, only looks to be coming from the thermostat housing, couldn’t feel any where the water pump bolts up, what should I do now?
 

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2003 Sonoma SLS ext. cab 4.3L / 4x4
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Check to insure housing/outlet bolts are tight (and to proper torque). Is there a chance that maybe the thermostat itself wasn't properly seated? Were all of the mating faces cleaned & free of gouges/ nicks when reassembling with the gasket? Also, there are threads here on the forum regarding t'stat replacement, and undoubtedly some youTube videos you can also reference for tips.
 

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Discussion Starter · #3 ·
Check to insure housing/outlet bolts are tight (and to proper torque). Is there a chance that maybe the thermostat itself wasn't properly seated? Were all of the mating faces cleaned & free of gouges/ nicks when reassembling with the gasket?
It is possible but I’m almost 100% sure it was seated properly and I made sure it was all cleaned off, but I didn’t put the paper gasket on because someone on here told be I didn’t need it since the thermostat has the rubber gasket, could that paper gasket not being on be the problem? Also yes everything was torqued, do I need thread sealer on those 2 bolts?
 

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2001 GMC Sonoma crew cab 4x4, 4.3L automatic
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It was a Jeep Cherokee that this happened to me on, but the aluminum thermostat housing was so warped that it wouldn’t sit on a flat surface without being able to rock it back and forth.

Just something to check.
 

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B4U Task Force Admin
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Before you start gooing stuff up, check the housing to make sure it's flat. All it requires is the rubber gasket around the thermostat. If you need to add paper gaskets and sealer...somethings wrong. That doesn't fix it, just puts a messy band-aid on it.
 

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Been there Done it
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Sure the thermostat is in right side up? You said you replaced the thermostat housing. Put the old one back on if it didn't leak and return the new one for a refund.
 

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1995 S10
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Just got done with that - same problem, everything super clean with wire brush and sandpaper, finally I put a layer of Permatex #1 all the way around especially the 3 bolts, worked. No leaks. We used to use permatex #1 on freeze plugs back in the 60s and 70s. Stuff's like iron.
 

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2003 Sonoma SLS ext. cab 4.3L / 4x4
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Can you/ have you confirmed that it is not the t'stat housing itself that is leaking? I'd inspect it carefully, looking for any (pinhole?) leaks, especially where the flange and the tube are welded together. Just another possibility to check.
 
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