I noticed my passenger mount had shit the bed so I replaced it yesterday. Easy job on a Focus with a Zetec engine. Took about 1/2 hour to do. After driving about 10 miles I heard a banging sound in the engine bay. When I checked, the top of the new mount had blown right off. For some reason the fluid inside got so hot and expanded, it blew up. The remnants ran through my belts and luckily didn't do any damage. All pulleys on a Zetec are on the passenger side, so that's what the banging sound was. In an unrelated/related (?) issue, I had changed the coolant tank at the same time. It sits right over the mount. That was leaking onto the mount before so I figured the antifreeze chemicals damaged the mount. I did not bleed the system correctly the first time so the engine did get hot. Would engine temps effect the hydraulic fluid if everything got too hot ? I've cycled the coolant system correctly since then, and bled the air out. The first mount had leaked out the bottom and the new one blew out the top. I'll go to NAPA at 10 am today to try and return the damaged one. I don't know if anyone else has a car with hydraulic mounts. I need to know how and why the new mount blew apart and is it heat related ?

because of how viscose hydraulic oil that is used in those mounts is, i would find it hard to believe that you could get it hot enough to pop the top off a motor mount like that.

Explosion requires pressure, pressure requires one of two things; vapor (don't know the boiling point of hydraulic fluid OTTOMH, but i know it's high), or rapidly expanding fluid. Neither case should be caused by the engine heat, unless it was still leaking super hot coolant all over the mount, which you said it wasnt.

Definitely some kind of defect on the part.

Since the top is now gutted out. The rubber on the bottom is doing all the work just fine. Not sure exactly what the fluid is suppose to accomplish. It wasn't much thicker than water. Wondering if I can fill the top with silicone. I was told some Mazda drivers have done this. Any thoughts ?

I don't see why not....the hydraulic fluid (like compressed air) is just there to dampen some of the motor's movement. By filling it with silicone (get a fairly stiff setting variety) you're effectively creating a poly motor mount, which should reduce engine movement.

i would say just parts failure, if the fluid had any chance of getting to hot ford would have caught it before

i would say just pay the extra few bucks and get a motorcraft replacement after you bitch out napa