Car overheats, even when driving at 70mph

Ahhhhh....

There is one important piece of hardware which was not on your replacement list.

Thermostat.

Please tell me you replaced the thermostat before you blew all that dough on all those parts! The thermostat is cheap, and usually easy to replace.

Did you replace it?

Sounds to me like your radiator is plugged, or else it's all clogged up with bugs, leaves, etc. Try washing it out from behind with a hose with decent pressure and I'll bet you'll be amazed at all the crap that comes out. If that doesn't work it may be time to have it recored or replaced. Also make sure your thermostat isn't sticking, although I don't think that's the problem as if it is stuck I'd expect it to overheat all the time, and A/C usage shouldn't affect it (although I suppose it might, due to the slight increased drag of the compressor.)

good luck

nate

snipped-for-privacy@hotmail.com (Mark) wrote in news: snipped-for-privacy@posting.google.com:

1. Has the cooling system been flushed and refilled with fresh every year? And, did you use distilled water, or tap water? I have seen this before, and the cause has been a calcium deposits in the head blocking off the transfer of heat from the metal to the water, or, in some cases, blocking the flow of water altogether.
2. Check the lower radiator hose. If the spring inside has corroded away, it could be collapsing from the suction of the water pump. This will block the flow of water.

The AC causes the overheat faster because of the additional power it requires of the motor, and you are increasing the temperature of the air coming into the radiator, because it comes through the condenser coil first, absorbing heat as it goes, therefore you have a lower temperature drop across the radiator.

When I pulled the radiator out of my old Astrol, I was amazed at the accumulation between radiator and A/C condenser. Fully 20% of the radiator area was blocked by leaves etc. You could not see it without removing the radiator, and it could not be washed out with a hose from either side. Rex in Fort Worth

You don't mention the thermostat. Over the years I have had a couple go bad. You could pull it, put it in a pot of boiling water and see if it opens fully. If it is more than a couple of years old you might just replace it anyway. FWIW DFB

Approximately 8/18/03 11:48, Mark uttered for posterity:

Check the radiator pressure just for grins.

I would think the water pump as a suspect except that I can't figure why the A/C being on would affect it that much... the heat load from the A/C is normally in front of the radiator where would expect water pumping needed... still, check the water pump and fan belt.

How old is the radiator, any chance it may be blocked internally or otherwise restricting flow?

Any chance there may be an air pocket in your cooling system?

The bad news would be a head gasket letting exhaust into the coolant.

Thanks a lot to everyone who are trying to help me here. I forgot to mention that I have a '94 Mazda Protege.

As I had mentioned earlier, I replaced everything possible EXCEPT for the Thermostat. I told the idiot mechanic to replace the thermostat, but that dumb guy couldn't find where it was located. But its my fault, I should have forced him to locate it and replace it.

But, if the thermostat is faulty, then the radiator cooling fan won't come on, right? In my car, I see the radiator fan running all the time. Even with the fan running, it is not able to cool the engine.

To summarize the responses I have got, either I need to replace the thermostat or the radiator itself. Is it easy to replace the thermostat myself? I have the car manual, but I don't have any experience working on the car myself. Is it worth to take the car to the mechanic to have the thermostat replaced or should I try to do it myself??

Thanks again,

-Mark

Mark, I had a similar problem with my son's S-10. I tried everything to no avail. I had looked at and cleaned the front of the condenser but it didn't help. Finally, I checked the front of the radiator behind the condenser and it was completely clogged. I separated the two and cleaned the radiator fins and haven't had a problem since.

Wrong. The thermostat doesn't control anything electrical, it opens and closes to regulate the flow of WATER. If its stuck closed, the fan will run like mad trying to cool the engine, but it can't because the hot water is never getting to the radiator.

Depends on how it's set up. In an old VW for instance, the fan is controlled by a thermoswitch in the rad, in which case the fan *won't* come on with a 'stat stuck closed. If the thermoswitch is in the engine block or head then yes the fan will still come on.

nate

The thermostat is usually an easy and inexpensive job. Then again, I have only done them on my domestic cars! :)))

Even a shop wont charge too much. You will have to drain some coolant from the rad. Unbolt the thermostat cover, remove the old thermostat. Clean all the surfaces. Install a gasket or silicon sealant (or both! ;) install the new thermostat, install the thermostat cover and bolt in place. Allow silicon to cure. Top up rad and you're done.

In some cases, you will have to remove the upper rad hose from the thermostat cover. And in some engines you may have to remove stuff so you can get at the thermostat.

The part should be in the $5 to $10 range. Maybe another $5 for a tube of HIGH TEMPERATURE SILICON sealant. And top up coolant as well. A few basic tools and a litte elbow grease. Give yourself a couple of hours.

Cant see a shop charging more than $50 to do this on most cars.

YMMV

Perhaps he meant that if the T-stat is closed, then no hot coolant will enter the radiator and the fan switches won't close.

Many modern cars have the the fans controlled by the EFI, and the coolant sensor for the EFI is likely located in the head(s) or block, so it will see the engine temp, not the radiator temp.

Some radiators have a double crossflow design where both the inlet and outlet tubes is mounted in the same tank, with a baffle between. If this baffle comes lose, then the radiator will leak from inlet to outlet without the coolant ever passing through the radiator.

I currently have this problem in my Pantera. When I start the engine cold, I can feel both the inlet and outlet in the radiator becoming warm after a while, while the tank at the other end of the radiator is cold. I need to open the tank up and fix the baffle sealing.

Thomas

I think you need to take a course on thermodynamics. -PapaRick

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Mark wrote:

No one mentioned the radiator cap. As I understand, you have to maintain pressure to control the boiling boiling point. It could be as simple as that. What does a bad cap look like ? Same as themostats. They look like the good ones..

OK, that wasn't too bright, but they made up for it with the elegant simplicity of their "sandwich" oil to water engine oil coolers (fit between the oil filter and adapter.) Cools in summer, heats in winter, no moving parts, no thermostats. A beautiful thing (I've added it to two VWs now.)

Of course, they barfed it all up by spec'ing a T-shaped hose to plumb it in (with one leg a different size, and too close to the water pump to splice in a plastic tee to do a jackleg repair anyway) and of course, after about 100K miles or so, they leak.

nate

It was the THERMOSTAT !! I replaced it and my car seems to be working fine now. Thanks to everyone who provided help.

The mechanic wasn't convinced that the thermostat could be faulty. Instead he thought the temperature gauge was faulty. But I forced him to replace the thermostat and it worked.

Thanks, Mark.