CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Pontiac GP running hot

Hey guys. I have a 2006 Pontiac Grand Prix. It has about 220k miles but I keep it maintained and it still runs good. Anyway, lately I’ve been noticing that when my car is sitting at idle the temperature gauge is going up, in fact today it almost went past the 3/4 mark while I was parking. Now, when I’m on the interstate driving at highway speed, the temp stays at or below the halfway mark. But if I’m town, off cruise control, and I keep needing to have my foot on the throttle, it is starting to creep up. The odd thing is when I parked the car, I checked the trans fluid temp, it was at 180 degrees. And in fact the fluid temp was at 120-130 even though the temp gauge was above the halfway mark.

Now to explain the maintenance I’ve done (as I’ve had this problem in the past). I had the radiator flushed once, then I had an intake hose replaced, but that fixed it for about a year, then it began heating up again, so I took it to a mechanic who said then thermostat was shot, so he replaced it and for about a year it worked fine, and now it’s happening again.

Any advice you could give (or possible pricing of any repairs I may need to do) would be most appreciated.

God Bless,
Brian Henegar.

First I’d pressure test the system.
Then I’d replace the radiator. Radiator flushing is not as effective as it sounds. There used to be a process called “coring”, where the small tubes were replaced, but in today’s economy and with today’s radiator materials it’s better to just change the radiator. And it’s more effective.

Brian, let me get a little more information, please. When the car is sitting, with the engine cold… did you check the coolant level in the actual radiator and was it full right up to the neck?

Was the coolant level in the plastic coolant expansion tank at the “full cold” level?

Have you had to add coolant? can you tell if it uses any?

I am quite familiar with GPs. :wink:
CSA

Hey there. I checked my radiator and the fluid wasn’t up all the way to the neck. Also I checked the reserve tank, but I have no idea where it should be filled to could you advise me?

I take it that you have not added any coolant?

The radiator should be maintaining its own full level, right up to the top. If not then I suspect a leak. You need to add a 50/50 coolant mix to bring it up to full and you’ll need to note how many ounces it took. When new these vehicles call for GM specified Dex-Cool coolant which is orange/pink in color.

At 200,000 miles it could have been changed to a different coolant (different color). See if you can ascertain it’s color. Different types of coolant should not be mixed. Let us know what you find.

If you look at the side of the expansion tank that faces the engine you’ll see a symbol (molded into the plastic) that represents coolant (liquid with waves) and a long arrow pointing downward from that symbol. The horizontal line that the arrow is pointing to is the coolant “full” level when the engine is cold.

Sometimes it’s easier to shine a flashlight down through the tank’s opening at the top and view the fluid level from the side. You can also peer straight down into the tank.

I would first determine how low the tank and radiator are and then we can advise you. With this information I can tell whether or not you probably have a leak and also tell you where to look.

Until this information is confirmed I wouldn’t drive the car in case it actually is beginning to run hot/hotter. That would cause a possibly minor problem to become a major problem.

Look over this information, look over the car, and come back. please, hopefully with more info. This is not easy to do online, but we can try. :wink:

When my Corolla acts like that, dash gauge moving into overheating territory during long idles, like waiting in line at McDonalds drive thru, it’s always been the radiator cooling fan temperature switch has failed and the radiator cooling fan isn’t coming on when it should. Next time it does this, keep the engine idling, pop the hood. The radiator cooling fan(s) should be spinning to beat the band. Are they?

1 Like

While I agree, it’s certainly possible that it’s a fan problem, but this jumps ahead of what I think Brian should check first. Whenever there’s a possibility of a cooling problem I believe it’s necessary to know the status of the coolant, first, before driving the car some more to check fans, etcetera.

I have a police/fire/EMS scanner that runs 24/7 at my house. When a call comes in for an unconscious person, the first thing that’s asked is if there’s a pulse and if the person is breathing. Then comes questions about history, medicines, allergies, illnesses, etcetera.

Certain things are critical to a car engine and engine oil and coolant are right up top of the list. They are the life blood of a car.

When it’s confirmed that the coolant is sufficient to safely start the car and also that it’s not consuming/leaking coolant the secondary questions can help pinpoint the problem. Fan is on my list and since I know these GPs and engines I have other ideas, too.
CSA

No disagreement there CSA. You posted some excellent advice above. I’m just offering my 2 cents is all, another idea beyond what you mentioned for the OP to consider. I think folks who post questions here understand it isn’t really possible to get an answer to a car problem with 100% certainty over the internet, and are mostly looking for an assortment of ideas so they’ll have something to work with.

1 Like

Runs fine on highway-heats up in traffic-not a thermostat problem. Fill radiator to the top, drive in traffic and when it gets past the normal mark, stop and see if the radiator fan)s) are running. If not, there is your problem.
Then find out what controls you fan, it could be a relay. temp sensor, fan control module or computer- I don’t know much about GM cars.

It sounds like after a year of operation the coolant level is too low to cool the engine, the vehicle is taken in for a repair whether it needs it or not.

A technician is not going to get paid for topping off your cooling system, he must find a problem and offer a solution in a short period of time. Those repairs may or may not helped.

You should refill the cooling system, check it for leaks and monitor it for loss. If you see a leak of there is a need to add frequently have it repaired.

BTW, this car should have modern electronics, no separate radiator fan switch to fail.