91 Tempo Cooling/Heating system problem

[tendrheartangel]

My 1991 Ford Tempo started having a problem recently. The car started overheating out of the blue, and when I turned on the heater to try to cool the engine, it blows nothing but cold air.

I replaced the thermostat and coolant temperature sensor, and now the car doesn't get as hot when I am on surface streets, but if I try running it on the freeway, the temperature guage goes clear to the top. It still has no heat.

I think there may be a blockage in the coolant system in the heater core, causing it to overheat more at higher RPMs and have no heat.

Does this logic sound right? Does anyone have any other thoughts?

[Mr3GTP]

How's your water pump belt? Sounds like you have little or no circulation. Could be a cracked head too, compression in the water jacket can cause air pockets which restrict flow. Give the pump belt a look, it could be slipping or gone altogether.

A loose belt will slip at higher RPMs. Also, check its tensioner pulley while you're under there.

[tendrheartangel]

We did check the belts and everything seems to be in good shape. They have about 1/4" play and aren't frayed though they do have a few minor cracks. (Will probably replace them anyway)

The funny thing about the overheating problem is that even when the car was showing completely overheated, I could still put my bare hand on the head. It was warm, but if the car was that overheated, I shouldn't be able to touch the head. Also, once I turn the engine off, then just to accessory, so the radiator fan is blowing, even when showing completely overheated, the engine temp gauge drops back to it's normal operating temp within about 5-10 minutes. I have never seen a completely overheated engine cool that fast.

The car runs just as normally when it is hot as it did before I started having the problem. It doesn't get sluggish or anything like an engine usually does when it is overheated. I also have ruled out a blown head gasket or cracked head because I have no smoke or anything unusual coming from the car, and there is no water or coolant in the oil in the engine block.

I have also checked for leaks from the radiator, block, water pump and heater core and have no leaks at all.

[Mr3GTP]

Well, that's different! Maybe a good system flush is in order, and also a thorough check of electrical connections. A bad ground could cause odd temp readings, etc.
As for the heater issue, are you sure the heat controls are working, the air actuall going through the heater core?

[tendrheartangel]

Yeah....the controls are working because until the night that it overheated the first time, I had no problems with the heat/defrost, although a couple nights before this started, I got a little "fog" on the windshield when I started the car, which I thought about in passing as a possible heater core issue.

This weekend, we are going to have a professional system flush done to make sure everything is clear. If that doesn't work, we will probably replace the heater core (which we can and have done ourselves on another car).

When we replaced the thermostat and sensor, we drained and did a chemical flush on the system, and after those things were done, we seemed to be doing a little better. Before we did that stuff, the car would overheat even on surface streets, but after, it only gets up to about 3/4 of the gauge on surface streets. I think the flush we did may have opened it up a little so we are getting SOME circulation, but not completely, and I hope a professional flush might clear the blockage completely.

Will let ya know what happens after the flush. Hopefully that will work.

[KimMG]

Don't discount the water pump. The vanes can wear causing poor circulation. After the car gets up to normal operating temp, feel both hoses going to the heater core. If one is hot and the other cold, then you have a clogged or restricted heater core. Are you losing coolant? Is the radiator clogged or restricted? Warm the car up to normal operating temp, turn off, disconnect the negative battery cable (to keep the fan from coming on) and feel the radiator for cold spots, indicative of clogs or restrictions.

[mechhound]

I would suspect the impeller on the water pump has broken loose and slipping, beings it started overheating out of the blue. This would also explain your heater not working.

[tendrheartangel]

Okay....we got the car running and not overheating....I missed a belt because I forgot that with A/C there are 3.....anyway, I replaced all the belts and now the car isn't overheating. I also have a heater now (YAY!!) Only problem now is that when I am running it (even on the freeway) the car never shows that it gets to normal temp, always shows cold...until I turn the engine off, then the gauge moves up to the normal operating temp that it usually would run at before this all started happening.

[Mr3GTP]

Two things I'd check; all the air is purged from the system, and the ground wire that connects to the passenger-side strut tower. Air in the system can cause odd readings from the sending unit, and a bad ground can also cause gauge abnormalities, as well as other issues.

To purge the air, I drive the right-front wheel onto a wood block or curb, making the cap the highest point in the coooling system. I then remove the cap (carefully! Best done cold) & run the car, topping off the rad, and squeezing the top rad hose slightly to 'burp' out the air. Sounds goofy, but it has helped in the past.
With the rad I'm running now, the cap IS the highest point lol.

[mechhound]

It sounds like your new thermostat is opening waaay too soon. I would do this test: let the car sit and idle with the heater and AC turned off. This would give you little to no cooling action. The car should warm up until your electric radiatior fan(s) kick on with your temperarture guage somewhere in the normal range. Watch the guage carefully to make sure you don't overheat the engine in case the fans don't kick on. Bottom line, I suspect your new thermostat is defective.

[Reg Saretsky]

the Car frorm hell

Try coatingthe elecvtricl connectors with dielectric grease, (Lightly) then use liquid tape to seal them off.

After 15 years oxidization, wear tear, builds up.
Congrats on keeping it running this far. Don't put too much money in it....