My son has a 1996 Mercury Mystique with the inline four cylinder Zetec engine. It started to over heat last week after drive if about 5 miles. I change the thermostat and then the water pump, but it still does it. I thougt maybe it was a bad head gasket blowing exhaust into the coolant. I did a compression test and they all were 120 psi. Now I baffled, I know if could possible be a cracked block, is there a way to check if the block is cracked other than tearing it down? Does anyone else have any other suggestions of what to look for?

Any help greatly appreciated.

BobG

 

You should be able to get plenty of help at contour.org. There are some extremely knowledgeable people there.

Any check engine lights? I would bet on a sender or sensor problem more than actual coolant problem. They can get contaminated by old coolant or just go bad.

Start the car and turn on the A/C. The fan should come on immediately. If not, the motor is burned out, or the sensor is not working properly. You could also check the large connector just foward of the coolant tank. That connector is part of the circuit that tells the fan to work and can get dirty and cause problems. Usually some contact cleaner and a Q-tip will do the job.

When it starts to overheat, does the fan get louder? The fan has a higher speed setting for that reason. My Contour (same car as your Mystique) read hot one day and the higher fan speed came on, but come to find out, the temp sensor was bad and the engine was not really overheating. Unless it is obviously overheating and running bad, I would use a tester to check actual coolant temp.

The sender for the gauge is on the bottom of the thermostat housing, you can see it pointing down between the radiator hose and the exhaust heat shield. Pull it and check the resistance. The temp sensor for the computer to monitor and turn the fan on/off is at the top.
Ground the white/red of the temp sender plug and the gauge should read full hot.
Worst case, they are both about $17 apiece. Not very expensive.

If there is not smoke or steam at the tailpipe, I would bet the head gasket and block are fine. Is there coolant in the oil?

Last but not least, the Zetecs are known to run "hotter" than normal due to the gauge not being the most accurate one ever made. For instance, mine points to the "O" on "normal" at operating temp, but another car of the same year can point to the "A" at the same temp. I have yet to see 2 gauges point to the same spot at operating temp.

HTH, and if you have any more questions, feel free to ask.

 

I finally got it figured out. The new thermostat that I put in was bad. I checked it in a pan of hot water and it opened a little funny, so I took it back and they gave me a new one. Now it runs on the O. When I replaced the water pump, I had to remove the overhead cam belt gears. One of them must have turned slightly, so the idle is a little rough. I need to find out how to get that changed back to normal.

Bob

 

My bad, I assumed that since the part was new it would work correctly. Glad you fixed it though

To properly retime the cams-
Remove the cam cover.
Each cam has a slot on the back. Use a large file or other suitable piece of flat steel to lock the 2 cams together in those slots. Then slip the belt back on.
The Zetec has no timing marks. The slots are the only true way to retime them.