Decided to replace the thermostat today. Old one was Cummins and looked good, but the seal was major checked out. No leaks when I started.

Cleaned everything up purdy, put in new NAPA thermostat and seal, and now it leaks. I'm sure the seal is in the right way.

What did I do wrong?

 

I personally re-use the old seal. Just coat it in RTV and install. Then let it set up for a hour or two, then refill. Never had a leak.

Is there not supposed to be gaskets as well between the housing, the lift hook, and the block?

 

I got mine from Geno's when I got the pump. No issues since I redid my head gasket about a year and 5,000 miles ago.

 

Got the parts from Geno's, I think. Had them for a year. Finally got a round tuit. Seal is the only "gasket" type part in the assembly.

I'm jealous.

 

[quote=j_ .

What did i do wrong?[/quote]
NAPA> I haven't got a good part from them in years. Could be a local thing though.

 

Was wondering about that. How much should the seal protrude from the assembly before installation. It only looks like .030" or so with this one.

 

I always smear some RTV on gaskets, seals, etc. No leaks that way.

 

One trick I've learned with RTV. If I'm making a gasket or seal that will have to be removed, ie rocker cover, Mercury outboard lower unit, etc. I lay the bead on one part, ie the rocker cover, then put a real thin film of oil on the other part, ie the head. Then I take the bolts down just far enough to form the gasket. Let it cure for a couple of hours, then torque to spec, which is usually pretty light. Next time, the "gasket" comes off with the cover and is in perfect condition. Just put it back on when through with the tappets. I think my Mercury XR4 LU is going on the 8th time or so with the same RTV exhaust block in it.

Another thing about RTV is it cures with water. The more humid it is, the faster it cures. Today I visited with the mechanic who knows, and he told me I was wasting my time with NAPA parts for the Cummins. I couldn't get the right parts before the weekend without spending big bucks for shipping, so I put the NAPA junk in, including buttering up the seal with RTV. I then filled the system with fluid. I'll wait about an hour before I light off the engine. By then it'll be pretty much cured.

<update> No leaks. Napa thermostat hunts excessively, as promised.

 

Funny how RTV needs humidity to cure, while paint needs dry air.

But RTV does have acetic acid (smells like vinegar) in it.

 

Actually, the acetic acid is a byproduct of the cure, when it reacts with water It quickly dissipates after the curing is complete.

Experience with RTV.....emergency boat repair when time is gold, as in got washed up on broken granite rip rap by an idiot with a houseboat running half throttle under a bridge during a fishing tournament. Pulled the boat onto the trailer, banged the rip halfway close and pop-riveted an aluminum siding patch buttered up with bath tub caulk over the rip. As soon as it tacked, threw it back in the lake. Hit full throttle in 5 minutes. Never leaked.