: Overheating



Tiaze
07-19-09, 12:12 AM
Got a 99 DeVille with 57K miles from a local auction. while driving back on a highway, smelled coolant for a half minute and gone. Drove around a town local/highway. A/C blow motor was bad initially so no A/C for a four days. After replacing the motor and using the system for two days, car overheated. It happened on a very hot day around 95 degree and after getting off of a highway and waiting at a traffic light. I noticed coolant steaming off of hood then checked DIC, which stated temp up to 230. Shut off engine. On a green light, started the engine, drove 100 feet. DIC showed overheated, shut off engine sign. Pulled over and shut off engine right away. Waited a while to go down to 197, opened the cap, pour water. Drove to a gas station, put green stuff 1 gal. Not enough, put another gal of pure water. At this point, I thought car ran without enough coolant, which caused the overheat. Picked up my son then drove home without A/C about 15miles. I was concerned while it happened cooling fan was not working, even when it was shut off right after overheated. The code reads P1258...overheat protection mode... But car was running with full power.

During morning commute, car was fine next day. So I thought the problem was fixed with enough coolant, just needed coolant flush then Dex-cool. But on the way back around five afternoon, coolant temperature went up to 225 and coolant burst out almost 2 gallon off of the cap.... Start driving again and coolant temp quickly went up to 230. Realized that there must not be enough coolant so pulled over again. Refilled with water. No coolant fan running.
When it reached 225, front top of rad hose was soft, meaning no coolant pressure there. Thinking thermostat problem. Or cooling fan not working properly.... Thermostat is replaced but fan is not working. Then I read it will activated when the temp reaches around 220. Haven't tried it that hot since I was afraid of overheat. But if A/C is on it works around 205. Some one suggested temperature gauge for cooling fan can be bad. Is there a such part? Is it cooling fan control mode? Any suggestion or help will be much appreciated. Thanks.

00 Deville
07-19-09, 12:22 AM
coolant temperature went up to 225 and coolant burst out almost 2 gallon.... Refilled with water

I'm confused where did this 2 gallons of coolant burst out from?:hmm:

Tiaze
07-19-09, 12:32 AM
It burst out off of the cap.

Ranger
07-19-09, 10:36 AM
Before you waste anymore time and money, go to Napa and get a Block Test kit and test the coolant for the presence of exhaust gases. If it is positive, you have a bad head gasket. If it is negative, then we'll look at the other possibilities, but DO NOT run the test right after adding coolant. Preferably after it begins to run hot.

00 Deville
07-19-09, 11:24 AM
It burst out off of the cap.

I was afraid that you were going to say that. Like Ranger said you need to test the coolant for exhaust gases. Unfortunately your year is prone to head gasket failure. Typically on the N* engine when the head gasket goes exhaust gases will escape past the head gasket into the cooling system... over pressurizing the cooling system. The cooling system cap has a safety feature built in in to relieve this pressure...dumping both pressure and coolant.

Tiaze
07-19-09, 06:03 PM
If the headgasket problem, then what? I heard replacing just headgasket will be impossible due to thread loss. So replacing engine?

Whatever it will be, thanks for your words to you.

MrEldo97
07-19-09, 06:46 PM
Head bolts pull out the block - s***ty engineering by GM. If you do have pulled headbolts you can Timesert the motor. Plently of info on this process available on line.

Good luck.

00 Deville
07-19-09, 06:59 PM
If the headgasket problem, then what? I heard replacing just headgasket will be impossible due to thread loss. So replacing engine?.


You are correct if it is the head gasket you would be wasting your money replacing just the gasket. You need to have either studs or timeserts put in by someone that is experienced with the N*. The motor has to come out so most of the money spent will be on labor... so do it once and do it right.

As far as replacing the engine... you already have a low mileage engine... if you go with a different engine that haven't been studded or timeserted you may run into the same problem. It's fairly common for the 1999-1997 engines.

There's a fellow forum member named 97EldoCoupe (aka Jake) that will do your head gasket and stud it... he's located in Ontario he also sells the stud kits. See his website below.

www.northstarperformance.com

Tiaze
07-21-09, 07:54 AM
Thank God! It turned out to be a bad temperature gauge that controls cooling fans. Coolant temp never goes up more than 222 F. That's when the fan kicks in.

I did some tests suggested by northstarperformance but showed no sign of gasket leak. I will still watch out the temp for the time being, but, looks like I got lucky.

Thank you all who posted suggestions, concerns and solutions.

83CADMAN
07-23-09, 01:14 PM
Thank God! It turned out to be a bad temperature gauge that controls cooling fans. Coolant temp never goes up more than 222 F. That's when the fan kicks in.

How did you determine the sensor was faulty? Where is it located?:suspense:

Mark C
07-23-09, 02:51 PM
Its in the end of the rear head (closest to the firewall) on the drivers side near the intake manifold.

Necrosan
07-25-09, 06:02 PM
That wouldn't make coolant burst out of the system.
Check your coolant for the presence of exhaust gases.

twinbopilot
07-26-09, 10:58 PM
Also check for a blocked purge line. It connects to the expansion tank near the radiator cap. Remove it and try to blow through it. If you can't, you need to clear the blockage. The car will overheat if this line is blocked. Blockage usually occurs near the water pump located on the top left (driver's side) of the engine. Remove the air filter box. Then you will see where the hose connects to a metal pipe pointing out from the water pump toward the left fender. That pipe can be unscrewed very easily and reamed out if need be.