1996 Chevy Lumina overheats. Radiator replaced, water pump replaced, thermostat replaced, heater core bypassed, temp sensor replaced. Air blowback into the overflow tank. Looks like it is boiling but it is cold. Car still gets hot. No water in oil. Does not seem to be leaking water. Fans do not seem to come on when they should. Hooked heater core back up. No heat. I do not know what else to do.

SOURCE: Over heating/ loss of coolent

If you are not loosing coolant on the ground. You may have a problem of a bad intake manifold gasket or worst a bad head gasket. The two things to look at are coolant in your oil, manifold gasket. Coolant out the exhaust, head gasket.

SOURCE: no hot air from heater, blower runs fine

The heater in your car depends upon a flow of hot coolant going through the heater core in order to get hot air into the car. If the heater core is partially plugged, it will restrict the flow. If you have a head gasket that is putting exhaust into the cooling system, it will eventually get into the heater core. When this happens there is no coolant in the heater core to make the air warm. If the water pump vanes have corroded away the result will be very poor coolant circulation causing the heater to not blow hot air. If your car is equipped with a heater control valve that is not functioning properly, the coolant flow will be restricted. One or a combination of these factors is likely the culprit in your case.

Since you state the 2 things you ruled out, that leaves only the water pump. Is the car running hot? The thermostat may be sticking as well... but im leaning toward the pump.

Dennis Mulford

• 1055 Answers
• Posted on Feb 26, 2009

SOURCE: 96 Deville Overheating....TroubleShooting

did you run a compression check? if so and its good then you have a blockage in the water jacket
if not then you have a head gasket leaking

Mark Carrington

• 192 Answers
• Posted on Aug 22, 2009

SOURCE: 1996 cadillac deville overheat..radiator?

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.

SOURCE: engine over heats 2000 cadallic deville northstar engine

flush your radiator first.with the thermostat out you should see the water moving if not bad water pump.this engine needs the thermostat to function properly and either a 50/50 coolant or straight coolant so it does not boil over.also make sure your fans are coming on