mcgarvey
Veteran CEG'er
Last time I had my zetec mystique up on the lift I noticed some coolant droplets hanging on the bottom of the transmission. I traced the leak to where the thermostat housing meets the cylinder head. My local parts supplier didn't have the o-ring seal in stock so they ordered it for the next day. In the meantime I checked out some Focus forums and saw that this is a common problem-- the ridge that holds the sealing o-ring in place breaks causing the ring to move around and fail to keep the coolant inside. In my case, when I took my thermostat housing off, the groove and o-ring were fine, but the side of the cylinder head was actually pitted! Pretty strange, especially since it's a rubber-to-aluminum mating surface. The pits were deep enough that simply replacing the o-ring and retorquing the housing down wasn't going to fix anything. I ended up using a liberal bead of RTV (Toyota FIPG, the good stuff that we use at work-- $26 a tube!) directly in the sealing groove in lieu of the o-ring. So far so good, no leaks.
That brings me to the question-- why would the mating surface on the side of the head get eroded like that? I've seen that kind of damage in heater cores and metal intake manifolds on cars where the coolant is rarely replaced and becomes acidic, but that doesn't explain my situation where the coolant has always been changed annually!
Has this happened to anyone else?
That brings me to the question-- why would the mating surface on the side of the head get eroded like that? I've seen that kind of damage in heater cores and metal intake manifolds on cars where the coolant is rarely replaced and becomes acidic, but that doesn't explain my situation where the coolant has always been changed annually!
Has this happened to anyone else?