i have a 06 5.9 and so does my neighbor and the thermostat gasket started to leak around 30,000 miles.. does anyone have any idea why?

 

I don't think there is a gasket. Has he tried tightening the bolts?

 

I changed mine in my 05 ( due to engine not heating up ) anyways all it has is a o ring that goes around the thermostat. Why it started to leak is a good question, check the bolts if you haven't already, if there tight then you may just want to drain the radiator and take the neck off the head and see if the o ring is damaged. let us now what you find out.

 

ill tell him tomarow morning.. this has happened before to you guys?

 

Nope. I have a 180 degree thermostat that I use in the summertime. I have had my thermostat housing off a couple of times on this truck and on my 03 and never had any leakage issues.

 

Dodge89W250
While I haven't had this issue with the '05, I have had it twice before, once with the '01 and once with the '02. Not sure what caused it, but it was the rubber ring around the thermostat that had started leaking. Both times the cure was to simply replace the thermostat. Haven't had an issue since.
mishkaya

 

Both the thermostat and the water pump use a rubber o-ring in a machined groove. There are no gaskets.

I had a leak similar to what he is seeing and it ended up being the water pump leaking and I replaced water pump and all has been good. No more leaks. I believe the leak was from the shaft on the water pump and either fan or normal road wind forced water up on block.

 

I noticed it last night that it had dried up antifreese all around the edge of the housing. When I took it off, I noticed that the seal on the old one was thinner due to wear than the new one, so it was being forced out the sides.
The only issue was tightening the bolts to 18 lbs like my book says. I broke one bolt at 15 and about broke a new one off while replacing that one. I never got them to 18 lbs. I was afraid I would break another one.

 

When I took mine out to modify it I found the factory gasket had been pinched under the termostat and was missing 1/3 of the rubber. It wasn't leaking though.