Hi everyone,

I've been having an engine overheating problem (DIC message:coolant over temperature. Gauges show it near 260 F).
It started all of a sudden. I've checked the front of the radiator, no blockage, engine fans seem to switch on, coolant is the correct level,

At times, it seems like the temperature hits a certain level (about 235, though it can go up to 250) and then backs off to 190 before it starts up again. I thought the fans were kicking in then, but it seems like the fans are on, even when the temperature is climbing to 250 or more.

It's been over 5000 miles since I had an oil change, could that be it ? never got an engine oil low message. Perhaps a faulty thermostat ? How do you check for that ?

Any ideas would be much appreciated!

 

To check the T stat you have to pull it out and see if its frozen. One easy way to find out if part of the radiator is blocked is to, let the car warm up when the T stat should open. Place your hand on the top of the radiator and move it across. If part is hot and the other side isnt the same temp you have a blockage in the radiator.

 

It it still has the stock programming then the first cooling fan won't come on until the temp reaches 225 degrees. The cooling fans come on and you say the coolant temp goes down to 190 then it starts all over sounds normal but the temp should almost never get to 250 degrees.

If the coolant level is normal, the radiator is not blocked and both cooling fans are coming on (not just one) then It may be a bad thermostat, maybe you should have the coolant flushed and change the thermostat to see if that helps.

 

clean out the radiator & AC condensor with an air hose or a high pressure water hose. It does not take much grass, dirt, sand or a bag to cause the temps to go up.

 

You have two radiators. The one that you can see when you look under the front of the car is the AC condenser. The engine radiator is behind that one. The "SPACE" between the two radiators frequently gets full of fine sand, grass, dirt paper etc.... Thats where you need to start. I would pull the top plastic shroud cover off and get a good look between them. Back flush the radiator and condenser fins with a garden hose. WARNING! Do not use a pressure washer on the fine jet setting. You will destroy the radiator and condenser fins! If you use one, only use it on the wide fan setting and don't get too close .

Once that gets all cleaned up, if you still have the issue, get a new T stat.

BC

 

Thanks very much everyone! I am going to try some of these things.

Here's a bit more info: I was seeing all these problems in city driving (NYC) constant stop and go. I took it to the highway this morning and all the time I was on the highway doing about 60, I didn't see the temps go above 190. It went to about 210 before I hit the highway, seemed to go back to 190 and then once I hit the highway, it stayed there. Once I got off the highway to idle a bit, it climbed to over 200. Its almost as if the air cooling was enough, so it makes me wonder a bit...

Appreciate all the help!

 

 

I agree with cleaning the radiators. Also, something to keep in mind is that above about 35mph, the fans do not cone on, unless the AC is operating. That could partially explain the rise in temps as you're cruising off the freeway...it's not uncommon.
Ed

 

Check under the front and make sure the radiator fins are clean. You could have some junk or a plastic bag from road litter stuck in there.

If the temperature is fluctuating, it could be a bad T-stat. It is either stuck or going. That is a pretty easy fix too. I have had a couple of thermostats go bad on other cars and the symptoms are exactly what you describe.

The fans running will have no impact on temperature if the thermostat is stuck. The coolant can't circulate.

 

I believe this would only be true if the thermostat were stuck full closed. The coolant temp does drop so I suspect the thermostat, if stuck, is at least partially open. Also, temperatures on these cars do tend to increase if driving around town in traffic. In fact, stock settings for both fans to run is about 226 degrees. I believe the first fan may come on at about 210, or so, but not sure about that setpoint.
Ed

 

If you are seeing temps as high as 260 the fans should be on. If the temps do not come down when the fan is on you should check for obstructions as mentioned above and you should also check your coolant freeze point with a hydrometer. If your coolant is more than 50% antifreeze the freeze point will be below -34 defrees F and your cooling system efficiency is reduced as there isn't enough water in the coolant to transfer the heat out of the coolant. I found this out on my VW Diesel many years ago when I had too much antifreeze in the coolant. The heater wasn't working well at temps below 5 degrees and a technician pointed out to me that dumping some coolant and adding a couple quarts of water would help. I didn't really believe him but I tried it and the heater started heating the car.

The low speed cooling fan is commanded on when the coolant temperature reaches 108°C (226°F). It is turned off if the coolant temperature lowers to 104°C (219°F). The high speed cooling fan is commanded on when the coolant temperature reaches 113°C (235°F). It is turned off if the coolant temperature lowers to 108°C (226°F). When the A/C is on and the coolant temperature reaches 85°C (185°F), the low speed cooling fan will be turned on at vehicle speeds less than 56 kPh (35 mph).

Bill

 

Great info. I've logged the numbers for future reference. Thanks!
Ed

 

 

Be sure both fans are turning. You can't tell by listening. You can't see the driver's side fan at all. It may sound as though the fans have changed to high speed but all of the noise may be coming from one fan running on high. Get a fan tester (a small stick from a tree) and poke it into the driver's side fan from the rear. If you don't hear a rattling sound, the fan is not turning. Look for: relay problems;or, ground problems;or, test the fan plug for current, engine & AC running. These fan motors do go bad and don't show a DTC code.

 

When I was installing my K&N kit.... I about **** my pants when I saw how much dirt and grass was in my radiator.... I took a pressure washer to it and it now runs 20 degrees cooler....!!

 

Fan tester! Are you from Arkansas???? That a RED NECK tool!!! Is that listed in the Snap On Catalog?

BC

 

If you can't readily locate a twig, you can always use a finger. Your friend's finger of course. (Gotta be safe)

 

I guess I should give a bit of background. Its an '02 coupe, built in '01. currently 45 000 miles.I bought it at 10,000 miles.

So I tried cleaning out the radiators and the space between with air.Today the temps stopped going down altogether and I had a brief instance where the temp topped 270 and I got reduced engine power.

Reading some of these posts (in other overheating threads) almost has me in a cold sweat over how much can go wrong. I dont have a home garage (live in the city) so there's only so much I can do myself.

I guess I could get a radiator check and flush, provided I could get it to a radiator shop. How can you tell what discolored coolant should look like ?

I did notice that a bit of coolant has spewed out of the tank after overheating.

What does it take to replace the thermostat (cost and effort)? Is that something thats easily accessible ?

I got an oil change done with mobil one and that seems to have only aggravated the problem.

Thanks!

 

Thermostat only takes an hour at the most. Cost is (im guessing?) 30 dollars. Flush and refill the radiator with distalled water and DEXCOOL! Thats about as basic as you can get!

BC

 

If your going to change the thermostat consider installing a 178 or 160 degree stat!