What can cause a vehicle to run hot, but not overheat?

Question

Anyway, I have a Grand Am 2003 V6. It only has 80k miles. My car ran great when I got it(used), but at some point it began to have minor temperature problems. It would always run a little bit hotter than it should. This basically just meant I couldn't keep it idling forever. At some point I took a drive for about an hour and the vehicle was running fine. I got to where I needed. On my way back home though it overheated. It didn't blow up or anything because I caught it in time, but it hit the redline. I checked it and it had no coolant at all. I let it cool off and filled it up with water and there weren't any leaks and it drove fine after that except for the before mentioned idle-overheating problem. This was about 2 years ago.

I ran over a deer a few months ago though and now the problems are worse. It was discovered that one of my fans was burned up, so that could have been the previous problem. Now though, the radiator has been replaced and both fans work and now it stays hotter than usual just driving. The temperature it usually should be at is about 200F. It now commonly stays about 205 and can get as high as 225 with just normal driving(note, 260F is red line)

One more unique thing about this. If my engine is at about 205 when I park, if I turn off my car and leave it for about 15 minutes, when I come back and start it, it will usually be about 215 or so. Basically, noticeably hotter after turning it off and back on.

I've checked for leaks -- There may be a very small leak somewhere. But it shouldn't be anything to worry about because I fill it up with about 2 cups of coolant or so after 3 or 4 months. So it's a small leak, if not just evaporation. And of course, I've checked to make sure I have enough coolant and that it's mixed properly.

And the only other thing(which is getting fixed soon) is that my air conditioner lines are ran wrong with one of the lines right against a heat shield on the engine, but that shouldn't affect the temp of the car should it?

So what could be the problem? I don't expect to fix this myself, but I'd love to be able to suggest to a mechanic maybe what the problem is instead of them tinkering around for a couple of very expensive hours.

Edit: I don't know how I forgot to mention this, but there is a hissing coming from my engine. I thought it was from my A/C(which is normal?), but I'm beginning to think it's not. Basically, I can hear a hissing that appears to be coming from within the air vents in the interior. The hissing is particularly loud when idle or braking and goes away completely while doing hard acceleration with it getting more and more quiet with the harder I press the accelerator.

Answer 1

First, if it runs hotter during slower speeds (the 25mph-50mph you mention), I would think this is a sign that you're not getting enough airflow through the radiator. This might be a fan issues, but it might also be some other obstruction that prevents sufficient airflow.

You said you hit a deer and had the radiator replaced as a result. I would check or get someone to check both for a vacuum leak (the hissing might indicate a vacuum leak although it shouldn't go away if you rev the engine harder unless it's a turbo- or supercharged car) and also check if all the ducting to the radiator (if your Grand Am has some, I would expect it to) and the undertray under the engine is present. If they've been damaged and haven't been replaced, this can mess up the airflow in interesting ways and can easily contribute to less airflow through the radiator.

Unless you live in a desert climate like I do, I wouldn't expect the sort of coolant loss you describe - it's quite a lot and evaporation of coolant were a problem we'd all be constantly filling up coolant :). In fact I'd worry about that even in the climate I live in.

I'd start with getting the ducting checked out and the cooling system pressure tested - every decent shop has the kit for the latter and if it doesn't hold pressure for a reasonable amount, you've got a leak somewhere and need to get that fixed first.

Edit: Given that you mention that the radiator was replaced with a used one, there is a chance that it might be partially blocked or at least not flow as well as it should. Flushing out the blockages depend how bad they are - you might be able to flush it out with the right sort of chemicals but there's no guarantee. The easiest way to find out if the radiator is suffering from blockages is to warm up the car properly until the radiator hoses get hot and then see if there are areas of the radiator that remain cold. Don't touch the radiator for that, either hover the palm of your hand half an inch over the surface or use an infrared thermometer. If there are blockages you should notice a difference in temperature.

Chances are that if the blockages are severe enough to affect the running temperature, it's time for a new radiator. Get a new one from a reputable shop this time, it's a lot cheaper than having to fix a head gasket that blew because the engine overheated.

Answer 2

This actually ended up being a very simple problem. Something so simple that I'm almost in disbelief.

My car has been running nearly straight antifreeze.(I'd say about 90% anyway) Everyone I'd talked to locally has said it should run even cooler doing that... but they're wrong. I emptied my expansion tank(not the radiator itself) and filled it with straight water. After a day of running it and letting it mix my car is now back to running at 200F and doesn't get hotter while idling or anything.

EDIT:

Just to finalize on this ancient question for future viewers. Running straight antifreeze was definitely the biggest problem, but not the only one. I never did find the cause, and I sold the car around a year ago because of that and various other looming mechanical problems (ie, would always stall out on first start, etc). Things I did and their results:

1. Actually use 50/50 water/antifreeze -- had a major result and kept the temps reasonable most of the time
2. Got cooling fans replaced -- was able to keep it cool enough that it survived a 16 hour road trip without too much worrying. If I idled a lot or was in stop/go traffic though it still got warmer than it should.. and a few times the fans would still randomly pop a fuse for some reason. I think the electrics was messed up in some way. Sometimes it'd be getting hotter and hotter, but then turning on the AC instantly cooled it down, indicating the AC fan was keeping the radiator cooler?
3. had radiator checked for blockages etc, had the thermometer thing (thing to controls when coolant valve is opened) replaced, etc.. nothing conclusive came of it

Only thing I never had done was have the water pump replaced... so maybe that would've been something close to it.. Just before selling it, I had the timing belt "tensioner" or whatever it's called replaced, and I don't recall having any problems after that point with the cooling... but that could've just been coincidence..

So glad to have a new car now that I don't have to worry about breaking down or overheating every time I drive it

Answer 3

You see, the problem with runnning with straight coolant--a don't know how that fad got started in the previous century--is that coolant has relatively little heat capacity; whereas water has very much (near tops) heat capacity--for which reason, the main coolant during summer driving is water, not antifreeze. The main purpose of commercial coolant/antifreeze (along with radiator cap) is to raise the boiling point and lower the freeze point of the water--that plus imparting anticorrosion qualities to the water. Because of water's and of antifreeze's separate and distinct advantages, the 50:50 water:coolant mix is typically found to provide the best compromise of advantages and disadvantages, for the widest range of average weather conditions... for all makes and models.

Answer 4

Have you replaced the thermostat and or the coolant temperature sensor. I have had a car which I thought was overheating have a bad coolant temperature sensor and there was actually nothing wrong with it. If that doesn't fix it I would replace the thermostat which is cheap and easy in most cars.

Answer 5

The hissing might be a vacuum leak, have your mechanic look into that.

When car runs hot or gets close to overheating, it is extra taxing on several parts of the engine and cooling system. There could be gasket that is leaking or a water pump that is close to failing, or you could just have a bad thermostat, but it sounds like the problem might be worse.

I would suggest getting it looked at soon, as running it hot might cause more problems.

Answer 6

My 2001 aztek with 120000 miles was overheating badly. Radiator had a leak and was replaced. Still overheating with new thermostat. Bottom line dexcool ate head gaskets up. Was losing Antifreeze thru cylinder. Replaced head gaskets and put in standard Antifreeze. Runs great.

Answer 7

I have had the same problem for years on my 2001 Grand Am. We have replaced fuel pump, water pump, thermostat, head gasket (since it redlined after thermostat change) and nothing worked. Same thing, I was fine as long as I wasn't idling places. But, I live in Wisconsin and really all fall and winter it is fine, but once it gets above 80, I have to watch it. My husband has really thought for years that the fan is just not kicking in like it should when it gets hot. He was going to configure the fan to always run on high or use a toggle switch but I have just gotten used to it so I continue to deal.

Answer 8

I have a 2005 hummer h2. 6.oL and normal temp is around 200-205 degrees. (I have a tuner on it so all temps are exact +- 1.5 degrees. I live in Dubai. Average temp here is about 110 during summer and 80 during winter. It's a desert people. So it's hot and humid. My hummer runs very hot 225 during summer. I tinkered with everything. I changed the belt fan to a duel elec fan set tip. Didn't help. Actually the belt fan kept me around 217.8. No leaks, pressure test was good, no damaged hoses and good head gaskets. As I drove around 70 mph it would constantly climb until I boiled over. Stop, refill and repeat. I was so confused. Changed thermostats to 180 (195 stock) and didn't help. Using the AC made it MUCH worse. 230 or above very quickly. Now I will say you cannot drive here without AC. End of the day was this. Use water!!!! I run 9.1 coolant. I take two gallons of liquid. Gym calls for 1 gallon dexcool and 1 gallon water. Hence 50:50. I drained and put 2.8 galls water, .2 dexcool and that was it. I stay at 205-210 heavy driving. 80 plus mph or dune bashing in desert. I also found I had a tranny problem. I was a shifting hard 1-2 gear and noticed (on tuner I had a tranny silenoid code) when that happens I would run hot again. My tranny fluid is also cooled by radiator. Fixed that and right back to 200-205. All issues solved. Now keep in mind I live in the desert and never worry about freezing so I don't need a lot of violent. You guys living in different clim don't do this!!!! Make it 50:50 or 60:40. No less. Otherwise you run the risk of freezing and that's bad ok? Hahaha hope it helps. P.S. The idea for coolant mixture came from an aircraft company. They know what there are doing. Hope this helps. Also I agree with briefly getting hotter when you shut down. If you do for 10-20 mins expect all the way up to a 30 degree rise in temp. It will cool very quickly on startup.

Answer 9

Just a comment on running straight coolant vs straight water, like Lex said, water has the best cooling capacity, while the antifreeze does not.

I've read that some race teams will run a mix of 8:2 or 9:1 water to antifreeze. The corrosion inhibition properties are not needed for a race engine that is rebuilt each time, and the higher ratio of water allows for better cooling, which allows for better aero capabilities. They also run the systems at much higher pressures than a passenger car.