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livelaughlove21's avatar

Why might my car be running hot?

Asked by livelaughlove21 (15715points) July 21st, 2011

I’m not very car savvy, so I’m sorry if this is a stupid question. Just answer it if you know. :)

Ok, so I drive a Pontiac Grand Prix and my temperature gauge is like this:

Normally, and for the longest time, the car stayed on 160 pretty much the whole time. Recently it’s been running at 210 but didn’t go any higher. I was told not to worry until it got into the red. But today and yesterday it’s been running between the 210 and the numberless big line above it. And then this morning it even went between the last big line and the red, but never touched the red and didn’t stay high for very long. It’s fine on the interstate, but when I’m stopping and going in the city it keeps going high, cooling off, etc.

I’ve had my low coolant light come on in the past and I added coolant to it and cleaned out the system, but it’s not on now. No lights are on and the car is acting fine other than the temperature gauge. It’s been a REALLY hot summer where I’m at, but I don’t know if that makes a difference. I’m scared to drive it home after work today. What should I do?

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12 Answers

YoBob's avatar

My first guess would be the coolant. If your low coolant light is not coming on it is possible that the bulb is burned out.

Another possibility is a stuck thermostat. There is a little valve that controls how the coolant circulates through the engine. When cold the valve is closed so that the engine can heat up, then it opens to circulate the coolant to keep the engine cool. This valve or the thermostat that controls it can go bad and keep the coolant from circulating properly.

You could have a bad fan clutch or damaged fan.

john65pennington's avatar

Stuck thermostat. You need to take your vehicle to a mechanic and have your cars thermostat checked. If its locked in the close position, your coolant cannot circulante around the engine block to keep you engine cool, Excessive heat can harm your engine.

livelaughlove21's avatar

@john65pennington How much might a new thermostat cost on this car?

livelaughlove21's avatar

Well I went out to the parking lot at work and found a huge puddle surrounding the front of my car. There’s absolutely no coolant in the reservoir and I was strongly urged not to drive it home. I think it’s probably a busted radiator. My car mechanic said he’s getting 4–5 busted radiators in per day because of the horrendous heat down here and people blasting their AC. So, I’m getting it towed to him and expecting a huge bill by tomorrow afternoon. Fabulous…

CWOTUS's avatar

No coolant “in the reservoir” may simply be a leak in the reservoir. All that does is collect overflow from the radiator (and it’s a fairly recent addition to cars, which never had these in the 60s and 70s or earlier). So I don’t ‘expect’ a busted radiator – in fact, I’ve never seen one ‘bust’ except from freezing. That surely hasn’t happened to you.

But it could be that your radiator, probably never having been flushed or adequately serviced in the past, has become ineffective due to accumulation of sludge and rust in the bottom of the coils, and for that reason simply isn’t working as well as it can.

Before you agree to pay for a new (or new-used / rebuilt) radiator be certain that the one you have is actually ruptured in some way. I suspect that you just need a good flush and refill with the proper coolant / water mix (because if you only added water as the level declined, then your coolant was too diluted, and no longer offers rust protection, which will help to clog the bottom of the radiator even faster – a vicious circle).

It would be a good time to check and maybe replace the thermostat, too. That’s a relatively inexpensive cost item, and the labor charge to replace it is normally very low because it’s usually easily accessed.

livelaughlove21's avatar

@CWOTUS Heat and pressure and coolant can eat away at hoses and can cause one of them to burst. A blown head gasket and brittle plastic can cause the actual radiator to burst. Weak spots in the radiator or a faulty or dirty radiator can also cause a radiator to become cracked.

What I was told by my mechanic and a few of the guys I work with is that with the 115 degree temperatures down here along with the AC causing the radiator to have to work even harder is causing them to crack, burst, or spring leaks. Like I said, the mechanic has replaced 4–5 radiators a day over the last few weeks. There are a number of reasons that this could happen.

If it’s not a busted radiator, I’m sure it could be other things, but considering all of my water/coolant was on the ground in front of my car, it wasn’t safe for me to drive home, so I think I did the best thing doing that. My mechanic will find the problem, whatever it is, and fix it and I’ll just have to pay it regardless of the price. Can’t get to work without a vehicle.

Pied_Pfeffer's avatar

This is a complete long shot of an answer. A friend and I were in her Trans Am, when the temperature gauge started creeping up the dial. We finally decided it needed to be checked immediately and took it to a shop. It turns out that a rogue plastic bag in the street got stuck on some portion of the undercarriage (?), and all the mechanic needed to do to fix the problem was remove it.

If there is someone at work who is knowledgeable about cars, you may want to ask him/her about it. There was a co-worker who was willing to take a look at mine once and offered to let me call him when I got to the mechanic’s. And I did. When it got to the point where they were both speaking in car-mechanic speak, I just handed the phone over to the guy doing the work. When they came to a mutual agreement, I gave the go-ahead. The next day, the co-worker asked to see the bill. He said that what I was charged for was fair.

CWOTUS's avatar


I think perhaps you misunderstood part of my response. “The reservoir” doesn’t contain all of your coolant, not by a long shot. If that’s all that you saw on the ground, then it might not be as bad as you think. If the car is cool (hasn’t been driven in a while and you can safely place your hand on top of the metal radiator cap) then remove the radiator cap and look for the coolant level in the radiator itself. If you can see the level, even if it’s down a bit, then the car is safe to drive in terms of “coolant level” (you can still have other problems).

I agree that age, pressure and neglect can cause a radiator or any other part of the cooling system to fail. Of course. But with the engine simply “running hot” then the radiator may be sending too much fluid to the reservoir and that may end up on the ground. Not “catastrophic failure” but “symptom of a problem”. If the radiator itself holds fluid and pressure while operating (this is NOT something for you to test!) then “it works”. The way you can verify that is by checking the thing while cool, and if there’s fluid visible – under the metal cap, not the reservoir – then “it works”. (If the engine is running hot even while the radiator holds fluid and pressure then that’s a symptom that the thing is running “badly” or may be overtaxed – but that is not failure warranting replacement.) Even if the fluid level isn’t visible – if it has actually blown that much out through the reservoir – then the car may be safely driven for a while if you simply top off the radiator itself – again, not the reservoir – and put the cap back. In that case, though, you definitely need to have the coolant (antifreeze) replaced to the proper level as well. Any competent mechanic can tell you (because they have an instrument to check what the balance is between water and antifreeze) when you have enough antifreeze in the system. (Antifreeze is required to raise the coolant level’s boiling temperature above the boiling point for water, which many drivers may not understand.)

And unfortunately it is very common to find unscrupulous mechanics who will be willing to replace an entire system for an unwitting customer and charge for “new work” to be done (even if it’s done ‘properly’), when a minor repair will suffice. I still maintain that “replacing a lot of radiators” means that your mechanic either has a lot of customers driving jalopies on their last legs, a lot of customers who take zero care of their cars… or a lot of customers who seem to be rich sheep ready for fleecing. Because the simple fact is that radiators do not typically fail in hot weather. Radiator hoses can burst at any time of year, of course, but radiators themselves typically fail after a freeze, not “overwork” because of excessive hot weather. I think a properly performed flush and refill with new water / antifreeze will bring your system back to normal specifications if it hasn’t actually failed.

What I’m telling you is that you might need a new mechanic more than you need a new radiator.

livelaughlove21's avatar

@CWOTUS My whole family has been going to this mechanic for years and we won’t go to anyone else. He barely charges us anything for labor and calls us and tells us what needs to be done to the vehicle before he does it so we can give him the go-ahead. He’s also done a lot of free work for us. I actually bought this car from him and this is the only problem I’ve had with it in 3 years. So I think I’m going to take his word for it on this one, just like we have for all the other cars of ours that he’s worked on. He hasnt’ even told me what it is yet, so everything I’ve said are just guesses on my part. But regardless, thanks for your input. :)

livelaughlove21's avatar

Ok, I got the news. I had some “hose seepage” as he put it, “nothing major.” He hasn’t told me all he had to do yet, because I’m at work and didn’t have time to speak to him, but I’m assuming he replaced the hoses and put coolant back in it. And it was under $100, so I’m happy.

CWOTUS's avatar


YoBob's avatar

@livelaughlove21 – Do whatever you can keep this mechanic happy. Having a mechanic you can truly trust is worth his weight in gold!

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