2001 ZX2 78K hard miles (all short, around town) Original Owner This posting is similar to the excellent one done by "paul01zx2" back in 2011. It seems his photos have been deleted, so I thought I could replace one or two of the more interesting ones for those of you with this same problem. My wife's 2001 Escort ZX2 recently developed a leak between the cylinder head and the black plastic water outlet housing on the driver's side of the engine. This failure is apparently VERY common on the DOHC Zetec engine, and IMHO the primary cause is swelling of the rubber sealing ring over time. The rubber swells to the point where its volume becomes greater than the volume of its groove, and it eventually ruptures the thin inner wall of the water outlet housing. Without this support, the rubber distorts even more and pops out of its design location. In my particular case, the engine would lose an ounce or two of coolant when cold, but system pressure would eventually push the ring back into place and re-seal the leak when hot. In this photo of the failed housing, the rubber sealing ring stuck to the head (left) with visible distortion on the upper-left side. The housing (right) shows a complete detachment of the inner wall of the groove from 10 to 4 o'clock. The swollen rubber ring is now much larger than the groove. Here are the parts you might consider ordering before you start draining coolant, with a couple comments for your reading pleasure: The Motorcraft RH154 Water Outlet Housing ($33 at RockAuto as of 5/2019) is essential. This part includes the rubber sealing ring at the cylinder head; you can see it in online photos of the new part. Some people recommend changing this to the 1998 version, but I did not do this. Aside from the fact that my wife likes to keep everything "original" (yeah, she's a purist) this would have required that I also replace the two coolant temperature sensors with their threaded versions. I figure that by the time this housing fails again in another 15 years, this car will no longer be my problem. Besides, the next owner would thank me for keeping it original... I found that a small wire brush did the best job of cleaning the corrosion pits on the aluminum head, and a small flat file removed any protruding areas. Slip the lower front port of the new housing into the bypass hose before bolting it to the head. A 10mm deep socket is ideal for all 3 housing-to-head bolts; torquing gently to 10 ft-lb is all you need to compress the sealing ring. Install the thermostat & sensors before you mount this housing on the engine. Since you have to move the thermostat over to the new housing, you should get a new rubber sealing ring; Motorcraft RG632 or RG633 ($5). Both of these are essentially a fat O-ring with a groove on the inside that fits over the edge of the thermostat mounting plate. The wider lip faces the outlet pipe (elbow). I used the RG632, and I think paul01zx2 used the RG633. They are quite similar; I think either one would work (neither is the housing-to-head seal). You'll need to re-use the special self-tapping screws on the outlet elbow (Torx T25) just snug. The thermostat is a Motorcraft RT1150 ($6) which is set for 190F. I bought a new one but the old one was still fine. I really like the clever design where the inner plate closes off the bypass port to force ALL coolant thru the radiator when the engine is hot. The thermostat outlet pipe (elbow) is a Motorcraft RH86 ($13). Some people have reported pinholes but mine was in excellent condition and could be reused. Just clean up the face where it seats against the rubber thermostat ring. There are two coolant temperature sensors in the housing. The one on top is a Motorcraft DY884 (Grey connector, for ECU, $19) and the one on the bottom is a Motorcraft SW6146 (Brown connector, for gauge, $20). In my case, the rubber O-rings on the old sensors were flattened from age and did not seal in the new housing. I didn't have time to shop for new O-rings and didn't want to spend $50 on sensors, so I removed the O-ring from each sensor and put a few wraps of Teflon tape in the bottom of the O-ring groove, then replaced the ring. The Teflon tape expanded the old O-ring firmly against the housing and sealed just fine. The old retaining clips can be re-used but new ones are available from Dorman as #800019 (2 for $4). Install the sensors in the new housing in the same orientation so the connectors will line up, and do all this on the bench before you bolt the whole shittenkaboodle to the engine. Consider which direction for the retaining clips so you can get them off later if needed. One of those 4-finger claw type grabber / pickup tools is the cat's meow when installing a clip on the lower sensor with the housing in place.