overheating 1995 Lumina 3.1L

[BMountan]

Recently my 1995 Lumina has been overheating. I have had the following things done via a mechanic: changed the thermostat, flushed the heater core, replaced corroded fan wires, and had engine test to make sure fans kicked in at the proper temperature - all this did not change the fact that the car still overheats. The mechanic believes that the head gasket may be going in it, though when the vehicle is running there is no coolant seeping into the crankcase. Also the heater will blow cold air just before the tempature level reaches hot and overheats. Has anyone else had this problem and if so what was the cause/solution. Or does anyone have any advice on what I should do next?

[cadgear]

A few things, first, if the coolant is going into the cylinders, you won't notice coolant in the crankcase. Second, what is the actual engine temperature, taken with a non-contact or a digital thermometer? The coolant temp sensor might be out, or the dash guage could be off.

If you're not losing coolant anywhere, then I'd look at the second option. If you are, look at either the head gasket or the more common lower intake gasket.

[BMountan]

Originally Posted by cadgear

A few things, first, if the coolant is going into the cylinders, you won't notice coolant in the crankcase. Second, what is the actual engine temperature, taken with a non-contact or a digital thermometer? The coolant temp sensor might be out, or the dash guage could be off.

If you're not losing coolant anywhere, then I'd look at the second option. If you are, look at either the head gasket or the more common lower intake gasket.

Thanks for your reply, I am having the sensor and guages looked at next week. I was told the engine is running hotter than it should which could mean the guage is out and not something more serious is what I am assuming is this a correct assumption?

[cadgear]

If the actual engine temperature is hotter than say 220, then yeah, you got a problem. The ECT feeds info to the PCM, so if the sensor is out the computer will see the engine hotter than it really is, possibly having adverse operation.

Unless you have a radiator or a passage that's plugged, or are leaking coolant, then this sounds purely sensor/electrical.

[Manny_boy]

...not to second guess your mechanic, but do you know if your mechanic bled all the air from your coolant system when the thermostat was changed?

You said your heater was blowing cold air, right up to the point before the car actually overheated. That suggests that there is an air bubble trapped in your coolant system, and that it was not bled properly. You shouldn't be going from cold air to hot then overheat. You should feel the warm air as the temperature increases.

[BMountan]

how do I find out if this is the problem and then how do I fix it?

[jeffcoslacker]

Originally Posted by BMountan

how do I find out if this is the problem and then how do I fix it?

Open the bleeder screws on the cooling system, open the radiator cap, coolant should come out. If nothing, fill with coolant until it starts coming out the bleeders. Close bleeders, drive or run until warm, then open them again, if any bubbles or no coolant, repeat. I agree, usually explosive overheat with no transition and no heat points to air.

[jeffcoslacker]

One caveat. If it is indeed a head gasket, this will force compression into the cooling jacket, and CAUSE an air pocket, which is what makes them act wierd like that. If the air seems like it never ends, and can't be bled, or if there seems to be extreme pressure in the hoses before the motor even begins to warm up, he may be right about the head gasket.

[Ginsengbull]

Blue Devil sealant.

1 capful at a time.