View Full Version : Engine heats up at idle (99 STS)

08-18-08, 04:21 PM
No exhaust gasses in coolant.. But if I'm at idle the temp slowly climbs up, if I rev the engine up to 1500-2000 rpm while the car is not moving the temp goes back down..
Obviously the coolant isn't circulating like it should at idle or something is wrong with the temp gauge.. I'm checking to see if anyone else has seen this or anyone knows the most likely cause of this (like one of the silly teeny hoses that it has everywhere clogged or something) .


08-18-08, 04:22 PM
How high does it climb? Are the fans going on?

08-18-08, 06:35 PM
Check the waterpump,belt,pulley, and tensioner, sounds like maybe it isn't spinning fast enough at idle.

08-18-08, 08:32 PM
".......idle the temp slowly climbs up".......perfectly normal for an electric fan cooled engine with a/c off. The engine will slowly creep up to 224 depending on traffic/ambient temps, then the fans come on low and it will creep down to around 198-208. With a/c in some cooling mode, the temps should run around 200-210, with higher readings in heavy traffic. Normal. You get off the local road and onto the Interstate or beltway and the temp slowly goes back down to 196-204. Normal.

As tateos and misfit said, check the fans for low speed on/off and the belt for the w/p........if you can push it easily 1/4" the tensioner is questionable.

08-18-08, 09:34 PM
Put a new belt on it.. I'll check again though..
It creeps up higher than it ever has.. the needle almost always before was straight up and never moved and now at idle it moves 5-10 degrees after a minute, then another minute it moves another 5-10 then another minute moves another 5-10 and i got it to the point where it said 'engine hot a/c turned off' and i revved it up to cool it down again didn't want it to go any higher than that. That was needle getting close to the red mark. Fans are on the whole time.. If it was the fans, why would revving the engine up in park make it get cooler? It should overhead more with the engine at 2000 rpm if the fans were the problem.

I've driven this car for many many years (it's a 99) and it never ever got hotter than the needle moving a few degrees to the right and then fans kick in and it moves back up straight again. This is definitely not normal. I will check the belt again to make sure.. I suppose that could be the problem, as long as the engine is above say, 1700rpm it's all good.

Could this be caused by something in the purge line being clogged? I took it off the overflow and it's not clogged there but it looks like it might be going into the (thermostat housing?) where there's this VERY SMALL diameter brass plug.. I'll have to read the service manual to see the operation of this unless someone can explain it to me.. (there's that and then there's another run that goes what looks like behind the engine and another one that goes on top of the engine in the front below the sight shield .. weird coolant setup on this thing.

08-19-08, 08:14 AM
Sounds as if there's no water circulation at slow engine speeds which could be either air in the system, partially clogged radiator tubes, or maybe a water pump malfunction.

Have you ever replaced the water pump ?? Seems I read something in here, a year or so back, that some water pumps had problems with a plate on the impeller coming off or some such.........

With the fans running the engine temp gauge should never go more than 1/8"-1/4" past 12 o'clock.......

The upper radiator hose (outlet) goes across the top rear of the radiator. The "lower" hose (w/p inlet) is a shorty that comes out of the center driver's side of the radiator. The purge line is a metered bleed that slowly pisses coolant into the surge tank airspace in order to keep the main system air/gas free. The surge tank has a bottom line which allows the tank to "float" on the system and take up the expansion and contraction cycles as the coolant heats and cools. The several other lines are heater supply and return and can be murder to service. Also in the radiator side tanks there may be an engine oil cooler and a transmission ol cooler. The engine oil cooler is in the "hot" side of the radiator, so it is designed to keep the engine oil at least as warm or warmer than the coolant.

08-19-08, 05:03 PM
There's a lot of 1/4" and 1/2" coolant lines going everywhere.. It's nuts! They even go through the alternator for water cooled generator I guess.
If something did come off of the impeller it would be stuck somewhere in there and that could be a nightmare to get out..
I never have replaced the pump but I might as well do it..
If one of those little teeny hoses are clogged, would that cause this issue?

08-19-08, 06:14 PM
Not sure that some small accessory line could cause your problem. GM quickly and quietly got away from the liquid-cooled alternator: the idea was a disaster.

08-21-08, 07:44 PM
Have you checked the water pump belt tensioner to be sure it is not rusted in place and is providing enough tension?

08-22-08, 12:13 PM
Yes the belt is ok.. THis is a really WEIRD issue..
I seem to have at least bandaided it by putting a new radiator cap on and putting more coolant in so it's a little bit above the like where it's supposed to be..

Can't do the water pump yet because I don't have the tool.. should be here next week.

08-22-08, 05:25 PM
If the water pump is not leaking, it's fine. Impeller coming off the shaft is feasible, but very, very rare. Your problem lies elsewhere. If the purge line is clear, then maybe the radiator needs to be flushed.

08-25-08, 02:42 AM
A mechanic and myself went over a lot of things and couldn't find anything.. the purge line is fine, the little brass fitting is pissing coolant out slowly, the fans kick on fine, it simply just gets hot at idle but not at 1500 rpm and I can't figure it out.. I don't want to have to take the whole system apart to find out what's going on :/ The radiator looks like a reallllllllll pain in the *@# to remove.. I already changed the thermostat and the belt.
Problems like this are aggravating.. I wonder what else could possibly cause it?
How could a plugged purge line cause this? How about a plugged line to the water cooled alternator? These lines are so small I wouldn't think they could cause the temps to go up higher at idle because the coolant would just go through the engine and not through the smaller pipes..
Could there be a lot of air in the system that isn't being taken out?

And to make things worse my CD changer stopped working today.. 'CD CHANGER ERROR' is all I get now, lol!, AND my ISC motor doesn't seem to have the strength to lower the idle for some reason unless I unplug it and plug it back in so I just left it unplugged until I can get another one..

Ghosts in the machine!! Ahhhh!! :P

08-25-08, 12:08 PM
The purge line purges air from the system. Air doesn't cool the engine. If it is clogged it will overheat. Have the coolant tested for the presence of exhaust gases. Might be a head gasket.

08-26-08, 06:34 PM
I did check for exhaust gasses, but I will check again for a longer period this time.

I still can't figure it out, and now I have an even stranger issue.. I drove the car a long time on Sunday, and I parked it in my driveway and then 24 hours later (without starting the car) I went to check the coolant to see if I had lost any and turned the cap and coolant came blasting out .. It still had a lot of pressure in there after 24h of sitting.. THAT is WEIRD.. Never seen that before..

Any ideas??

08-26-08, 08:51 PM
Sounds like there was air trapped in there somewhere pushing against the coolant. Start the car cold with the cap off and look for bubbles in the tank.

08-26-08, 09:46 PM
I did.. I let it run for a while and it fills the coolant to the top of the tank and overflows.. it doesn't come out fast but it pushes a little coolant out of the top of the tank with the cap off while it's running..
:/ I'm really at a loss here.. I don't want to take the radiator off and all the coolant system and intake manifold, etc.. :/

08-27-08, 08:07 AM
foos........Your last post....tank overfills and runs over.......Try again; fill the system to just above halfway, cold, leave the cap off and start the car. Watch the coolant. (Just water by now ??) If it comes up in the tank, let it continue as long as it wants to overflow. Does the coolant start to bubble at some point ? Not boiling, bubbling.....hard to make a judgement call, I know, but a necessary call to find out if exhaust gas is what is causing the system to overpressurize.

The earlier post about pressure in the system overnight does not sound very encouraging, by the way........

The intake manifold is dry....no coolant associated with it. No need to remove it.

08-27-08, 11:20 AM
Just to clarify what I and Sub are saying, running the engine with the cap off will lower the boiling point so it will eventually start to overheat and boil. That said, you should have a good 4-5 minutes I would expect to observe it before that starts happening. If the coolant level starts to rise immediately while the engine is still cold, I would suspect exhaust gases being pumped into the cooling system.

08-27-08, 12:58 PM
I took the cap off and the coolant level was pretty much overflowing even cold.. I started the car and let it idle for 5-10 minutes and the coolant level just rose very slightly and pushed a little out of the top but very slowly and took a while for it to rise.. What concerns me is that it's all the way to the top of the tank when it's cold which doesn't make sense.. it's like something is stopped up somewhere in the system, and letting it sit for 24h and still having a lot of pressure in the system? That really doesn't make sense.. I'm really hoping it's not a head gasket because that's a lot of work to fix for just a gasket .. :/

08-27-08, 04:18 PM
Overflowing when cold is not a good sign. I would test the coolant again or have a cylinder pressure test done.

08-27-08, 04:56 PM
I'm really hoping it's not a head gasket because that's a lot of work to fix for just a gasket .. :/

It sure is - more than you know!

08-27-08, 08:45 PM
So this leads me to ask this question...

Is there anything else this could possibly be BESIDES a head gasket issue??

08-31-08, 05:23 AM
I had 2 more tests for exhaust gases which came up negative... Two mechanics think it's the radiator that has a blockage in it and that certain sections of it are overheating and overpressurizing and causing problems. Does this sound like a possibility?
The car is 10 years old and this is the 3rd time the coolant has been changed.. The other times had the 'bars leak' type stuff (some sort of ground root) put in it and this time I didn't put it in.. I seriously doubt that has anything to do with the issue, but it is something I thought I should note on the off chance that it does :P

08-31-08, 12:33 PM
Certainly could be a clogged radiator and the sealant tabs could be the cause. Maybe you can just flush the radiator (or have it power flushed) and see if that helps.