I've got an annoying and persistent small coolant leak at the back of my thermostat housing. It's been on-going since last winter when I changed my thermostat because the engine wouldn't warm up. Solved that....but I can't get rid of the stupid leak at the O-ring. The book I've got says the housing bolts are torqued to 18 ft/lbs. The leak stops for a while and then comes back after about a month. Always in the same spot. I've changed the O-ring and even applied some high heat sealant as well after the 3rd attempt to stop this. Both mating surfaces are clean and un-damaged. Does anyone no if the torque spec is 18 ft/lbs or is that not enough for the 6.0 diesel.
I guess the up side of this is....how fast I can remove and replace my air cleaner and intercooler pipe.

 

An o-ring sealed joint requires that the two mating surfaces are flat and have no scratches across them. If the joint leaks I would inspect both the o-ring groove on one joint and the flat surface on the mating joint for the scratch that is likely there.

Any scratches that are located across where the o-ring seats will cause a leak. These scratches can be removed with fine emory cloth if they are not too deep. Make sure that the joint is still flat after any emory cloth polishing.

Joint sealer actually prevents the o-ring from doing its job and is about the same as using no o-ring at all. If there is a deep scratch you can fill the scratch with epoxy and then polish the surface flat so the o-ring will seal.

Sometimes I think that a standard gasket and sealer was the best method for things like thermostat housings...

Lou Braun

 

Can you eliminate the O ring and make a gasket? That would probably cure your leak.

 

I checked the 6.0 manual that I downloaded and found the torque spec was 17 ft/lbs. I just finished pulling all apart again and checked the housing bolts for torque. I set my wrench for 18 and to my surprise; turned both bolts in almost another 1/4 turn before it clicked. I think what happened is when I torqued these a month ago, I was working outside and it was cold out. A month ago we still had snow. Today it's like a summer day. The engine was warmed right up while I checked and found the leak. Maybe the gasket and O ring were cold when installed and have softened up and seated as it got warmer out. The leak only showed up again yesterday.
The sealant I used before is a gasket maker type for High heat. Previously when I had it apart; I inspected both surfaces closely. No gouges or scratches on either surface. But maybe I missed it. Sometimes my eyes are not the best. Anyway everything is back together and so far, no leak. I think I'll keep my fingers crossed though. Hopefully third time's a charm. The original bad stat was changed in January at near -30 out. Even my gargage with the heat on was not that warm.