1996 Mercury Sable DOHC 3.0L. It has been overheating...started slowly while driving uphill and in traffic. Now overheats when you let idle for about 15 min or so.

We replaced the thermostat, no difference...replaced the water pump. After we pulled it out impellers looked fine. Installed a new one anyway, no difference.

We have an OBD II, but doesn't read with any error codes. Temperature gauge does indicate that the vehicle is heating up. Coolant has been changed several times, while replacing the parts, but never came out looking dirty during any of the changes. Verified that both fans are working. We tried to run it with the heater on full blast but couldn't tell if it was running hot or not. It was hot outside already, but I'm guessing that it is not putting out much for hot air. Feeling pretty stumped about this...anyone have any ideas?

 

How did you verify fan operation? And why unable to tell if it was running hot w/the heat on full blast? You are in need of a coolant temp sensor or a thermal fan switch. Or just run a hot wire to the fans(is that how you checked them?)and then to a toggle switch inside the car. Let me know.

 

We had verified that the fans were working by looking at them visually, assuming that because they came on that they were working properly.

Since my last posting we discovered that the fans were running continuously even after the car had been shut off and key pulled from the ignition. We pulled the fuse and came back to it today. After putting the fuse back in, the fans started immediately. We ran the car and when the OBD II was reading at 195 degrees, the fans just shut off and wouldn't kick back on. After that the temp steadily increased.

During that time we verified that the heater is working...blowing hot air. The **** to control the heat had cracked and was not turning properly, but the heater works fine.

We are guessing that the CCRM or fan control switch failed. I'm going to price a new one tomorrow.

 

By CCRM or fan control switch...I meant they are the same thing. Manual lists it as a CCRM...everyone seems to call it something else. ha

 

I have heard of people hardwiring in their fans to the ignition and then the fans would run whenever the car is on. I would like to repair the car with by replacing whatever is malfunctioning...If it is the CCRM I have been told that it could have an effect on the cars fuel efficiency as well.

 

Hardwiring is is a shortcut of last resort or if you need a quick fix and can't diagnose the problem. So you are right, fix it correctly. Still sounds like your fans are getting ***-backwards instructs, which means I'll stick w/my original diagnosis. Good luck and let me know.

 

It seems we fixed it yesterday after we replaced the CCRM--car idles smoother than what it was. Watched the temp on the OBDII...thermostat opened around 206 degrees, both fans kicked on low at 208 degrees and hit high around 216. Temperature plateaued around 226 or so.

 

206'' is high for any t-stat to open isn''t it? Isn''t 226'' too high of an operating temp?

 

I agree, but it is not showing any other problems. We did put a hotter plug in it. It plateaued at 226 after trying to recreate the problems it was having before...speeds under 35 mph and just sitting idle for extended periods of time.

 

As long as your satisfied. But my Sable never gets close to those operating temps, I''d be afraid of warping the heads or melting the gaskets. Good luck.