NORTHSTAR ENGINE OVERHEATS

check for exhaust in the cooling system. norstar has head bolt issues, allows head to leak combustion into cooloing system, pushing out coolant. Extremely expensive to fix CORRECTLY.

There are two other issues that also happen, and check these first: there is a small coolant hose 1/2 inch or so, that bleeds air from the block, it can plug, check it carefully,

Some water pumps have an impeller that fails, pretty quick overheat, though.

the head bolt issue is more mysterious, almost intermittant, but definately load related, when heat goes up, like going up a hill.

occasional sticking of the thermostat may be the culprit if it has not been replaced or may be seizing up

When a Cadillac (Northstar) overheats, It will give the message to change the oil. If you run a Northstar and keep running it long enough it will start shutting off cylinders and stop the A/C compressor to help protect itself. In this condition I would check for a blown headgasket. Possibly your technican will find the problem. Could also be stuck thermostat, dirty radiator Thanks

The Northstar engine in this model is bad to blow head gaskets. Pressure from a cylinder will overpressure the coolant system and all the coolant will blow out. When that happens the engine will overheat. I fixed mine but it cost about $1500 in parts and tools and 5 weeks. If your coolant level is fine, check your fans and your radiator. One fan will come on when the AC is on or around 230 degrees F I think-They are designed to run hot.

Whatever you do, NEVER allow this engine to overheat and always use the correct antifreeze (DEX COOL) or you will damage your heads severly. The heads were made from aluminum so there is a very serious warping issue on the 1998 Cadillac Northstar engines. There should have been a recall but wasnt, ended up costing me 3 thousand USD to fix the engine problems I had but she now runs fine. I only had the car 4 months before this happened so someone prior to me owning evidentaly let it overheat on too many occassions and I had no choice but to fix cause I was still paying on the car!! Good luck

It is probably a head gasket issue if you have replaced the thermo and the pump and it still overheats. You probably can drive it 15 minutes or so and then the gauge starts soaring towards overheat shortly there after. Under completely normal driving conditions. Northstar engine's actually don't overheat not from bad head gaskets (they aren't the defect issue) but the inferior bolts holding the heads to the block. The bolts have been found to be pulling out of the Northstar's soft aluminum block(this is the actual problem but it's blamed on the gaskets). Causing spaces between the block, gaskets and the head that allows hot exhaust air to seep into the coolant flow chambers. This why your have coolant bubbling out of the top of the overflow valve under the hood after only short drives. Under normal operation the engine is literally boiling it's own water supply. The head bolt issue is a design flaw by GM and one that leads to a great number of Northstar engines being crippled at well under 100K miles of driving. Only remedy is to have both heads pulled off the engine, the head bolt replaced with new gasket and you're all set. Bad new very labor intensive whcih = a several thousand dollar repair. I had it happen to my 1998 Concourse Deville. I feel your pain.

First of all you need to check your coolant return bottle level, it's probably low, and needs coolant added. Heater will be starved for coolant, if level is low, thus, cool/cold air comes out. Try to add when engine is cool, to avoid getting sprayed with hot coolant. Leave cap off for a while, turn your heater on (not defrost) and let engine run up to temperature, and add more as needed while you watch level. Rev engine slightly and hold it for 5 seconds or so, every once in a while to help circulate coolant, and remove any air in system. If you have an actual rad cap, that you can remove and watch flow in radiator, that's even better, for adding and bleeding air out same way. Make sure your rad fan is working as well, and once you get it topped up, and heat back working, I'd seriously consider having a system pressure test done, as you obviously have a leak somewhere if the level went down to the point of overheating, and heater was starved for coolant. Keep an eye on that return bottle level until such time you have it checked, to avoid more damage to engine.

There is no need to purge the air out of the cooling system as it is self purging on the northstar engine.
The most common overheating problem with the Northstar engine is a blocked purge line. It's job is to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.If the hose is clear, check for blockage at the nipple on the tank or trace the hose further back until you locate the blockage.

Check for coolant flow at the Purge line,this is a common problem on the Northstar.
There is a small diameter hose coming from near the top of the coolant tank,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.If the hose is clear, check for blockage at the nipple on the tank.

Check for coolant flow at the Purge line,this is a common problem on the Northstar.
There is a small diameter hose coming from near the top of the coolant tank,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.If the hose is clear, check for blockage at the nipple on the tank.