6.0 thermostat
 

Had a problem with my engine not warming up. Went for the easy fix and decided to change the stat. I found some good info on FTE as usual and decided to tackle it myself. Replaced no problems, torqued to 18ft/lbs, filled it up with antifreeze and took fo a drive. Everything appeared to be good. Engine warms up quickly now and I have heat again. I checked my coolant level again yesterday and I was down 1/2 gal. So I started looking for the leak. Thermostat housing, right at the seam. The O ring hadn't sealed and I had a stream of coolant coming out as soon as the system is pressured up.
I pulled the air box, inlet pipe & intercooler pipe. Drained the cooling system and pulled the housing apart. I got a new O ring and replaced it. Installed the new thermostat, being careful about correct torque on the bolts. I put the hoses back on, filled the cooling system, leaving the intercooler and turbo inlet off so I could see if it would still leak. Started the enging and it leaked immediately. Same spot, right through the O ring.
I think I'm going to have to re-install again with some high heat silicone to stop this drip. Each time I've taken it apart I made sure the mating surfaces were very clean.
Anybody got any tips or advice, I'd appreciate it.:-banghead

What did the old oring (I guess it would of been new if you just replaced it) look like? Any gouges or small cuts or etc if so it might have gotten pinched? I usually use just a little grease and spread it litely on new o-rings to make them stay in place and help seal or a high temp silicone like you said. Just a thought.

Thats what's weird the O rings looked fine. No cuts or nicks. I'm thinking of going with the high temp silicone.

Leak fixed........:-jammin. High temp silicone did the trick.