I had a coolant leak that seemed to be coming from above the oil pan on a 1996 Blazer 4dr 4wd. I have since traced the leak to the threads on the inlet heater hose fitting (see photo) that comes from the top of the intake manifold. I have some thread sealer (see photo) that I believe would be appropriate, but the fitting seems to have something like regular plumbing pipe dope on it. Would my existing thread sealer work here?

The rubber washer that was inside the fitting on the threaded side (see photo); what is this washer for? Do I need it?

The fitting looks fine, but could the fitting have corroded through?

 

Glad you found the leak. The sealant shown will work fine, just make sure all the threads are clean and dry before assembly. It looks like standard NPT threads on the fitting end so I don't see why a rubber washer was used there. Hope someone else knows.