Freezing and Overheating... fun!

Hey people!
Well I'm posting from Canada, where mother nature just decided to make it -40c with chilly winds.
This is where the fun part comes... rather amusing...
My 96' (3.1L) lumina (well my dad's) has a problem overheating and blowing cold air out of the vents.

So here's the details
- The engine overheats super fast; within a matter of about 10 minutes, the temperature guage is already in red. When I popped the hood, I saw that the fan was running nonstop, but the engine wasn't cooling.
- In park, I revved the engine at 1500 to 2500 a few times, and the longer I held down the pedal, the engine would seem to cool (well at least the guage said so)
- When I revved the engine, the heater fan would begin to blow hot air. Whenever I'm not revving the engine, it just blows out cold air.
- Also when I drove on the highway for a solid 15mins, and then parked and popped the hood, I saw that the fan was on, BUT, the coolant was at the very top of it's container-- seemed like it wasnt flowing into the radiator.

So any ideas on what's going on here / how to fix this up?
My gut feeling is telling me that it's the thermostat .... some ppl say it's just air in the system, and others say it's the water pump .... what do you think?

I believe the cold/hot air issue is just a symptom of a over heating car, getting air in it, etc. fix the over heat problem and see if heating isnt ok then. Go simple first, replace thermostat, and go from there.

Ummmm, I'm not sure a thermostat is going to help this one. There is most likely air coming from somewhere (headgasket?) into the cooling system, and it's making it's way to the heater core or the water pump is just wheezing on its last breath. I'd take it to a shop and have the system checked. The water pump is inexpensive and easy to replace.

I've had that happen before, it sounds like you have a large air pocket in your system, you definately need to purge your cooling system of the air. You have two small valves to do this, one above the water pump and another above your thermostat... Open them and wait untill you get a steady powerful stream of coolant coming out of each one bofore closing them... Drive the car around ofr a bit and repeat. Keep checking it and you will eventually get the air out of the system. Hopefully that's your only problem and you dont have some sort of internal damage sucking air into your coolant. Definately check all yor fluids to see if they are being mixed also, and smell your exhaust to see if it smells funny.

Don't ever rule out a headgasket problem. I'm helping out a friend with her car. Same issue. It would overheat then cool back down. Everything was replaced like the thermostat, water pump, raditor flushed, ect. with no resolution. I decided to tear apart the engine. This is what the headgasket on cylinders 2,4,6 looked like:

http://www.jdb1941.net/lumina/0228061634.jpg



http://www.jdb1941.net/lumina/0228061634a.jpg



When the car was running, cylinder 2 was acting like an aircompressor to the cooling system. With the engine off and not started for like a day, coolent would leak into cylinder 2 causing it to miss for about 2 minutes during warm-up. I'm quite amazed that the car actually ran like this!

I would suggest to see if your loosing any compression in any of the cylinders. If you are, then you may want to look into getting the headgaskets replaced.

holy hell that headgasket is horrible!

you ain't kidding there buddy!

that's kinda amazing...
to think that the car was still running with that kind of headgasket.

but yeah, since it's super cold up here in Canada, we've left the car parked in the driveway for a while while using the old rusted 92' nissan sentra (aka 'the box') to get around.

first thing when spring comes is to get under the hood and check out the thermostat.. and work my way from there.

umm... yeah i'm not much of an expert with this stuff... but what's the best way to get at the thermostat in this kinda car's engine? in fact... where is it?!

I would say you've got a bad intake gasket or blown head gasket. The problems you are experiencing are classic symptoms of both. The best bet is to do a compression test. If one or more adjacent cylinders are low on compression, you have a bad head gasket. If compression tests ok, you have an intake gasket bad, both very common problems on these engines.

how would I do a compression test on the cylinders.... ?

my knowledge of engines and servicing them is limited to what a chilton manual can show in diagrams :)

I have had the overheat on the gauge and no heat from the heater on my '95 3.1. I am convinced that there is a small exhaust leak into the coolant due to gasket failure. A theory is that the hot gas would not open the thermostat and therefore the engine overheats even though the coolant at the heater core is cold. I replaced the thermostat, my dad replaced the water pump, bled the air, but nothing changed. It works fine without the thermostat but of course not much heat from heater. My dad figured out something in between - drill a small hole in the thermostat (to let the gas leak from the engine out), then the hot coolant can open the thermostat. He did this and it has been working for about 2 years now. Quit working once and I found a BB plugging the small hole that was drilled. I know it has some kind of leak but so far this works and cost me nothing. I get a low coolant light now but the coolant is not low - presumably the gas bubble near the sensor. Step on the gas harder and the light goes away - I think the bubble moves away from the sensor. Only issue I have now is misses on a cylinder or two right after a stop. Other than that it runs perfect. I found somewhere that it is the intake air temperature sensor? I disconnect the thing and tell no difference in running other than the "service engine" light comes on, so maybe that tells me it is bad. I'm to cheap to spend the $35 for a sensor until the thing stops or else I know that it is the problem.

Blown Head gasket ( not negociable )

I'm liking compression in the cooling jacket on this one too...

Ever watch and see if the overflow tank shows evidence of constant air purging when it's running? (bet it will)