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That time I ignored the 'always replace the thermostat housing' rule on a 2015 Ford F-150 | Auto Mechanics - Discusd

That time I ignored the 'always replace the thermostat housing' rule on a 2015 Ford F-150

I was in my home shop last month, working on a neighbor's truck with a coolant leak. The leak was clearly from the gasket, not the plastic housing itself. Everyone online says to just replace the whole housing assembly, a $120 part, but the housing looked perfect. I cleaned the surfaces, used a good gasket, and torqued it down in the proper sequence. It held for a week, then started weeping again. I had to eat the cost of the new housing and do the job over. Maybe the plastic warps just enough? Has anyone else had a housing look fine but still fail to seal?

3 comments

3 Comments

tessagibson7mo ago

Oh man, that plastic housing rule is there for a reason. I fought the same battle on my old Explorer. The housing looked totally fine, no cracks, felt solid. I even used that fancy grey RTV everyone swears by. It sealed up great for about three hundred miles, then it was just a slow, steady drip right down the front of the block. I was so sure I could outsmart it. Turns out the plastic gets a tiny bit of a curve to it over the heat cycles, so it'll never sit flat again. You can't even see it.

jaken237mo ago

Yeah but "never sit flat again" feels like a stretch. If the housing is truly intact and you do a perfect clean and prep job with the right sealant, it should hold. That slow drip could have been a tiny bit of leftover oil in a bolt hole or a spot you missed cleaning. I've seen guys reuse those plastic parts for years without a single leak. Sometimes the problem isn't the part, it's just the process.

campbell.evan6mo ago

Used to argue with my buddy about this exact thing. Thought he was just wasting money on new housings. Did the same job twice last year and finally had to admit he was right.