: Head gasket = overheat while driving or idling?

11-14-06, 03:14 PM
I've posted some issues with my car before. It's been a few months, and I've either been working horrible hours, or been sick, and have not been able to even take the vehicle anywhere to be looked at. I have a 96 Deville with overheating problems.

I happen to work in the Auto Insurance field, and work with some self described ex-mechanics, and I'm getting conflicting reports, and was just hoping someone could settle a question for me. As I read through posts here, I'm confused as well.

I was under the assumption that if there is a head gasket problem, the vehicle will overheat while DRIVING not while IDLING. My Caddy heats up to normal range after a cold start, and frankly, I think I could drive a few thousand miles on the highway and it would never rise above 196 degrees. But if I'm stopped at a light for more than a minute, it will begin to heat up. Stay idling long enough, and it will overheat. When the light turns green, and I take off, within a minute, the temp starts to go down and will eventually go back to 196 and level off there until I have to stop again, no matter how hot outside it might be. Although I have noticed that since the temp has dropped here in Florida, the time it takes to warm up at lights is much longer. But it still happens.

Without fail, every day, that is how it goes. Luckily, I drive less than 10 miles each way to work and back. If I can do it without hitting any lights, it will never rise above 196. I've got in the habit of turning the car off at a light if I've hit too many of them, and the temp creeps to 228 or so. The minute I restart the car and take off, it immediately cools back down. On occasion, I have had to drive farther than to work, on the highway, and runs like a dream and never goes above 196.

So, anyone here able to settle this for me? Does my specific situation lead anyone to believe it's a head gasket, or would a head gasket give me conditions exactly opposite, with it cooling off while idling, and heating up when driving.


11-14-06, 03:47 PM
The engine isn't even approaching hot until you get to 240 deg. Are the fan's operating? 196 is actually a little cool. You seem to be describing a normally running engine. Does it boil and steam? Does it lose coolant?

11-14-06, 03:50 PM
Sounds like your radiator fans might not be operating properly; although 228 degrees is not hot as far as your cooling system is concerned.

Open the hood and idle the engine with the HVAC in an air conditioning mode. Both fans behind the radiator should be spinning; you will have to look because you cannot hear them.

11-14-06, 03:54 PM
i've read through your previous posts, looks like you've had a spell of bad luck.
now, you say the car is overheating, what exactly do you mean?
does the car actually overheat to the point that coolant is expelled from the surge tank?
does the car regularly require topping up with coolant?
when the car is sitting idling, do the cooling fans come on?
does the use of the air conditioning affect the coolant temp at idle?

first thing to check is that the airflow to the radiator is not blocked, look carefully at the a/c condensor and see if the fins are straight.
if the cooling fans come on, does the temperature stabilise or does it continue to rise?
the thermostat might be faulty, even though you changed it.
try taking it out and seeing if the car still gets hot.
if the radiator has good airflow, the fans come on and the temp carries on rising to the point of coolant coming out of the surge tank it is possible that the water pump is faulty. the impeller blades can corrode so that at low engine speeds the pump cannot move enough coolant to the radiator. (some new jaguars have plastic blades that have been known to snap off!)
of course there is the possibility that you do have a bad head gasket, get the cooling system pressure tested to find out.
of course there is the chance that the only thing wrong with your car is that it is getting old and your temperature sender/gauge is faulty.
i have known cars that the temperature gauge moves a hell of a lot during normal operation of the engine, some cars have had the gauge right into the red zone before the fans came on, dropping back to under a third of the way when the fans cut off.

11-14-06, 04:11 PM
Ok, so I'm guessing that there is no single answer to the question of whether or not a head gasket leak will cause heating up while driving/cooling while idling, or heating up while idling/cooling while driving?

I'll try and answer the questions posted so far...

As far as the temps are concerned, I realize that 228 is not bad. But 228 is when I turn off the car because if I'm going to be sitting at a light for 5 minutes, and it's already at 228, it ABSOLUTELY WILL get too hot, and go in safe idle mode. I turn the car off at 228 so that it doesn't get any higher.

If I start the car and not drive, just let it sit in the drive way and idle, it will warm up normally to 196, breifly cool down to 194 (I'm guessing as the thermo opens), and after a minute or two, starts to heat up. At 221, it will again level off for a minute or so (the fans kicking on?), and then begin to heat up again. If left to it's own, it will eventually overheat, with coolant boiling and coming out of the overflow. Driving it like I have (making sure it never gets above 228 if I'm stuck in traffic by shutting the car off till the light is green), I have lost zero coolant.

As said before, I have not had the time to check the surge hose or belt tensioner. The radiator has been replaced during the time this has been a problem, due to the tranny reseviour bursting. The water pump is less than a year old, and the since the temp, while driving, warms to 196 and then stops, I'm guessing the thermo is fine. If I hop in my car and drive on the highway, it will never overheat. Stop and go traffic and it will heat up to danger temps if I have to sit for too long, every time.

11-14-06, 04:27 PM
so, new radiator, new water pump, thermostat appears to work, cooling fans work.
overheats only during extended idling.

are all the hoses correctly fitted and are they not kinked or blocked in any way

have you checked to see if the a/c condensor is blocked?
it sits in front of the radiator and if it is damaged in any way it will obstruct the air flow to the radiator, causing a possible overheat situation at idle.

apart from that you really should get a cooling system pressure test done.

11-14-06, 04:42 PM
Check the water pump tensioner to be sure is is not rusted and is providing enough belt tension. Also check to be sure that the purge line is clear and flows coolant. Doesn't sound like a head gasket to me.

11-14-06, 05:36 PM
me neither, the fact that the motor cools off as soon as the vehicle moves makes me think that there is a problem with the water circulation or airflow through the radiator
i suppose that there is the chance that the coolant cap isn't quite holding the pressure.

11-14-06, 05:43 PM
Get out the garden hose and spray the bugs out of the radiator from the backside.

11-14-06, 06:08 PM
Smelling coolant out of exhaust pipes is a telltale sign to HG problem yet your car overheates ,right ?
If so I don't think you have a HG problem .I was having similar symptons with '96 STS .The car was pretty nice when highway driving but when I was hit at the light and waiting or in a congested city the temps was hitting red level .Go figure
And also it was losing coolant I assume smelling coolant has anything to do with losing coolant .

11-14-06, 07:03 PM
If it is not losing coolant it's not HG's.

From your first description it is cooling fans. Have you checked them? It takes about 30 seconds.

11-15-06, 08:03 AM
This doesn't sound like a serious problem at all, so don't be worried. :) Good luck.

I would say it the fan or water pump. When you move I am sure the oncoming air helps a lot, so its just not being cooled properly at stoplights.

11-15-06, 07:51 PM
Sounds like the head gasket issue that so many of us have dealt with including my Caddy. I played the same game as you're playing. New radiator, water pump, thermostat and housing, belts, hoses, everything possible! The only solution that finally fixed the problem that you have described - head gasket replacement. All is fine now. Don't play the game any longer than you have to. Do the gasket change a.s.a.p. Just my thoughts after going through the same thing a few months ago.