1997 Deville Overheat

[97DevilleLac]

I have a 1997 Deville that is loosing coolant and overheating at highway speeds. I have to put about 1/2 a gallon of coolant every 40 miles. When i go over 70 mph the temperature start climbing fast into 240's. The problem is getting worse, it is loosing more coolant. I smell coolent around the engine but don't see a leak. New water pump and thermostat. No water in the oil, or oil in the water, so I am not sure about the head gaskets. Any suggestions? Thnaks!

[Ranger]

If you are smelling coolant, either it is blowing out of the overflow or you have an external leak. Do a cooling system pressure test to verify an external leak. Do a cylinder pressure test or a coolant exhaust gas test to verify a head gasket leak.

[97DevilleLac]

Thanks for your reply I will check it out, I also wanted to know if 97 deville's have a bleeder to release the air out of the cooling system, if they do where is it located? Thank you

[Ranger]

Yes, but it is automatic, this IS a Cadillac after all. See that 3/8" line coming out of the water pump housing and running along the forward cam cover and then into the upper side of the surge tank? That is the purge line. It's purpose in life is to purge the system of air and route it into the surge tank where it can be vented. Pull the line loose at idle (engine cold so as not to burn yourself). There should be some coolant flow. It will increase with RPM. If so, plug it back on. If not, that may be your problem. Locate the obstruction and clear it.

[misfit6794]

Sounds like a headgasket issue to me, check the tail pipes for coolant, thats the only thing that would really eat that much coolant. An obstruction will make it push out the overflow tank, but so will a headgasket. I wouldn't drive the car, to run it that hot, you could crack a head or block, and do some major engine damage.

[Lerpstah]

If you loose coolant through the overflow tank/hose, it should be fairly easy to detect. When I got my N* flushed, the braniacs overfilled the system and coolant would be pushing out of the overflowhose.
This is just a hose that comes out from under the tank cap, about 30cm long, goes downwards between the tank and the engine.
Check if the tip of the hose is wet.
Allthough, the amounts you are talking about should leave a puddle under your car.
This hose also pushes out coolant if you get combustion gasses in the coolant creating an increase of pressure (indicating a failed hg).
I had a Toyota engine fail on me because of a leaking hg, the coolant seaping into one cylinder increased pressure 'till the piston pin broke and took out bearings on the cranckshaft with it...
As in your case, there was no oil in coolant nor vice versa.
Take a good long snif at the exhaust fume for coolant smell.