: 2000 DeVille Overheats

06-18-08, 03:32 AM
Check Coolant Level message when surge tank is filled to cold mark. I can drive for about 10 miles and the temperature gauge will be at half of the range. Then it jumps to 1 bar above halfway , and the quickly moves up 2 bars. I will then get the " Engine Hot " message along with the "AC OFF" message. I then need to pull off the road.
1. Surge tank is at the right level when checked on cold engine
2. Cooling fans are working properly.
3. No coolant leaks noticed on the ground or on the engine block or hoses.
4. No AC is running while this error occurs


Feedback appreciated

06-18-08, 09:42 AM
Tony, go to your local NAPA dealer and pick up a coolant test kit to see if there is exhaust gas present in the coolant tank. Also, from cold, pop the hood and remove the surge tank cap. Start the car and observe what's going on in the tank: Is there coolant running from the small hose connected to the top section of the tank? Is it steady or does it have quite a bit of bubbling ?

Read up on head gasket failure here, in Seville, and down in Northstar performance.

06-18-08, 01:51 PM
Or the low tech way, stick your finger in the tailpipe when its cold and rub the sides, if there is coolant in there, your hg is shot. The engine was revised in 2000 to prevent hg failures, so it may be the purgeline is clogged, or your waterpump has failed you.

06-23-08, 02:19 AM
Heres what I have tried so far
1. Filled coolant to "COLD" marking with 50/50 DEX Cool
2. Ran car with surge tank cap off to "burp" the system of any air,,hopefully
3. Ran dry applicator into exaust pipe, no evidence of antifreeze in pipes.
4. Ran car with surge tank cap off, observed anitfreeze moving and bubbling up.
5. No evidence of antifreeze on the block or ground,,( would'nt a blown headgasket spray/leak out antifreeze?)
6. Checked upper radiator hose, damn thing is hot, can feel flow thru it.
7. Checked air flow tube that comes out of filler neck on surge tank, no blockage.
8. Both cooling rans are running.

From what I have been reading,
A whole surge tank replacement may be needed.
A cleaning out of the surge tank may be useful, but what are the odds.
Air bubble in hose from surge tank to water pump

All of the above..this ones got me baffled

06-23-08, 09:56 AM
tony, The headgasket problem on the Northstars is not a "blown" gasket, per se. One or more cylinder head bolts loses its thread grip and allows the head to "lift" slightly, introducing exhaust gas into the coolant while the engine is running. This rapidly overheats the coolant as well as overpressurizes the system so there may be some coolant loss in aggravated cases.

The kit I mentioned in another post uses a chemical detector system to test for the presence of CO2 and exhaust byproduct in the coolant by measuring the gaseous content of the (normally closed) airspace over the coolant in the surge tank. That's the only way you can really determine if you have a compromised gasket: they don't leak fluid to the ground, and, if caught in time, usually don't leak coolant into the oil (instant engine death).

#4......if you had coolant "moving and bubbling up" that's a problem. There should be NO bubbles from the bottom tank hose: that is the connection which allows the tank to "float" on the system, receiving expanding hot coolant and returning contracting cooler coolant to the system upon engine off cooldown. The only "bubbling" you should see is IF the purge line (small one from top of tank to engine) spits a small amount of gas or vapor as it purges the main system in order to keep the water pump from cavitating. That's a constant bleed setup, sort of like the pump setup in a fish tank.

Mark C
06-23-08, 12:37 PM
Did you actually see water flowing in the purge line? Disconnect the line at the surge tank and stick it into the open radiator cap hole on the surge tank with the engine cold. Start the car and you should see a good amount of water flowing in that tube. If you don't see water then the line is plugged somewhere, most likely at the barbed fitting on the thermostat/waterpump cover on the drivers side of the engine. If you don't have water flow diconnect the hose at the thermostat housing, and water should shoot out of the barbed fitting with the car running, if not its plugged. Run a 10 penny nail, or something similar into the hole in that fitting to clear it out. You will have to go in about a good 2" to get to the open end of the fitting.

When you have the surge tank open and the engine running, does the level change in the tank if you increase the engine speed? If so that a sign that there is an air (gas) bubble somewhere in the cooling system that needs to be burped out.

The water pump is turning, you did check the drive belt and the idler pulley didn't you?

If the line is clear and water is flowing thru that line, run the exhaust gas in the coolant test.

06-23-08, 02:42 PM
One thing to note is that if you try running the engine hot [operating temp] with the surge tank open you will have coolant gushing out. NorthStar doesn't like to be run hot w/ tank open. Thermostat being open just pushes hot coolant out the tank with no pressure holding it down.

Cold engine start w/ tank open AND bubbles showing in the surge tank point to HG problem. K_C

07-03-08, 02:58 PM
Thanx for all the responses, this forum is a great tool.
Brought the Caddy in today , and yes, there is exhaust in the coolant. Well **** my ozone.They want to replace the gasket, and total could be up to @ $4,000.00, from dealer service shop, and car, at best, is worth maybe $5000--6500, if Im lucky. Again, i appreciate all of your insight


07-04-08, 12:21 AM
The engine was revised in 2000 to prevent hg failures,They should have revised the N* with a different motor altogether. http://www.youtube.com/watch?v=Ml4_TZzWVTs&feature=related