: 99 Northstar burning coolant somewhere!



AEI
08-18-07, 05:55 PM
Ok, I have a 99 Deville with 110k miles. It has been using coolant consistantly since i bought it, although it has never had white smoke or visible signs of a leak. I thought it was a crack or gasket leak into the exhaust port. I typically ran 2000-3000 miles before Low Coolant message came on. I would add coolant and keep going.
Now however, the low coolant message does not come on but the engine starts running hotter and eventually overheats. Most of the time when i see the coolant temp creeping up on 250, I can turn off air, stop and idle engine and the temp comes right back down...then I a good for another 50 miles or more before it does it again. And I can ususally run at least 150 miles before engine temp starts going up. It still uses coolant just more of it now. I tried Mendtite stop leak stuff, but after a week it still hasn't changed. I also left the system under 22lbs of pressure all night long without the slightest drop!
Aside from ripping the engine apart what else can I do?

zonie77
08-18-07, 06:05 PM
The test you did will not show a head gasket that is starting to leak. You are not putting enough pressure on it.

Have an exhaust byproduct test done at a radiator shop.

The combustion pressure in the engine is in the 1000psi range.

At this point it may or may not be HG's. You have to start diagnosing it.

AJxtcman
08-18-07, 06:28 PM
I see water pumps, water pump covers, cross-over gaskets, short black hose coming off the water pump cover, short green hose coming off the back side of the cross-over, steel lines that run above the rear exhaust manifold, the two heater hoses, the third heater hose going to the surge tank and the surge tank (the brass piece breaks free of the plastic tank)

Zorb750
08-18-07, 10:17 PM
First, make sure it is burning it and not dumping it.

zonie77
08-18-07, 11:41 PM
The coolant pressure test would test a the hoses etc. Occasionally you'll get a leak that only leaks at certain times, temps, conditions. Leaving it on overnight and not losing any coolant is not real promising.

Definitely have the exhaust gas test done next.

99_WHITE_STS
08-19-07, 07:55 AM
Sound just like the symtoms I had with my 99 STS. Head gasket leaks. I finally got tired of "jumping" around to find the cause, and did a pressurization test of each cylinder, so that I would know exactly what was going on. I removed all the spark plugs, and using a 1/4" wood dowel, I brought cyl. #1 to top dead center. I then screwed in the hose that come with my compression gauge, with the schrader valve removed, and applied 120 PSI of shop air. My pressure tank on the cooling system was filled to a 1/2" below the top. If there is a HG problem, the tank will gradually rise to overflow. Do each cylinder, following the firing order. It is very important to have the piston on exactly TDC, or the 120 PSI will throw the piston down. Although there are a number of ways to reach TDC, I used a 3/4" open end wrench on the balancer nut, along with an allen wrench on the shaft of the power steering pump as an assist.
My wife could drive the car to and from work with no temp problem. There was nothing visible on the spark plugs, no steam in the exhaust, and no water in the oil. This cyl. pressure tests showed leaks in #1 and #3 on the rear bank, and #4 on the front. I had no reason at that point to try other tests, my my opinion would be, that a cooling system pressure test would not necessarily show pressure drop, because the cylinders would leak, only under high pressure. Hope this helps !

AJxtcman
08-19-07, 01:04 PM
The coolant pressure test would test a the hoses etc. Occasionally you'll get a leak that only leaks at certain times, temps, conditions. Leaving it on overnight and not losing any coolant is not real promising.

Definitely have the exhaust gas test done next.

NO
You may not find a leak in the steel line about the exhaust or a hose. Yes you would think that it will, but it is a small leak in this case. 1/4 gal a month? teaspoon a day?

Zorb750
08-20-07, 01:40 PM
Well, tablespoon a day if a quarter gallon per month, but good point...

Check the radiator cap, make sure it's not bad. Pressure test doesn't test that, hence also my dumping question earlier. A bad cap will cause slight evaporative loss. If you have a tester, you will also notice the mixture getting heavier on coolant and lighter on water as it goes on, assuming you add 50% each time.

AEI
08-20-07, 07:02 PM
Well, tablespoon a day if a quarter gallon per month, but good point...

Check the radiator cap, make sure it's not bad. Pressure test doesn't test that, hence also my dumping question earlier. A bad cap will cause slight evaporative loss. If you have a tester, you will also notice the mixture getting heavier on coolant and lighter on water as it goes on, assuming you add 50% each time.

I am definitely losing more than a tablespoon a day! About 1/2gallon per 150miles! Not so bad execpt I run an average of 200-300 miles per day in my business!
I am worried about the expense or getting this leak fixed as well as the so called issues that many have told me about getting the Northstar engines to seal back up after being torn down! Any advice on this?

AEI
08-20-07, 07:16 PM
I see water pumps, water pump covers, cross-over gaskets, short black hose coming off the water pump cover, short green hose coming off the back side of the cross-over, steel lines that run above the rear exhaust manifold, the two heater hoses, the third heater hose going to the surge tank and the surge tank (the brass piece breaks free of the plastic tank)

Wouldn't all of these be seen from under the car when it's running though? I can run the car for hours in my garage without so much as a drop of coolant on the floor under it...even with it running at 2000rpms!

Ranger
08-20-07, 08:08 PM
A small external coolant leak, like from a radiator side tank for instance, can be hidden from view. To make it harder to find, the coolant seepage will evaporate before it drips making it almost impossible to find. That's why pressurizing the system when cold and leaving it overnight will cause it to eventually show itself.

z06bigbird
08-20-07, 09:47 PM
250 degrees = likely cooked engine.

AJxtcman
08-21-07, 12:44 PM
Wouldn't all of these be seen from under the car when it's running though? I can run the car for hours in my garage without so much as a drop of coolant on the floor under it...even with it running at 2000rpms!

No
They removed the sand from the coolant. This means that it can evaporate cleaner and leave less residue