I've read a bunch of threads here and from googling but haven't found a solution to my problem yet. Maybe it's basic and I'm missing something simple.

The car is a 2000 Sunfire 2.2 5spd with about 200,000mi on it. I've had it for about 70,000mi over 4.5 years and it's given me zero problems that I can remember other than a dead battery and I can't really blame that on the car. Runs like a top, gets great mileage and burns no oil.

The oil looks fine, no coolant sludge.
The coolant looks fine to me. Not pristine but not oily or dirty.
The car has heat from the heater.
The fan or the fan switch seem to be bad. Might have killed the fan with excess use... It turns freely by hand but I haven't jumped 12v to it yet.

I don't want to cloud the issue but I should say this is a second car now and I've been playing with it since last year to get mileage out of it. From August 2012 to a few days ago the car had an airdam under the bumper, the lower grille opening fully closed off and the upper grille opening about 90% closed off. The "normal" operating temp went from 195 to 210-215 but other than that everything was good even when I drove to GA and was in 90 degree temps. (I hit 41mpg for a full tank on the way home from this trip)

Recently I've been doing some light towing and for the first few trips (different days, air temps 45-60degrees) there were no temperature issues. On the third or fourth trip the temp started to climb and I was only able to control it by throwing the heat on high, this brought the temp back down and kept it down as long as the heat was on. Now I know it isn't the grille blocks I had on there causing this directly because I'd been towing this trailer several times recently and the time it overheated the trailer was empty! I tore them off anyway, the grille blocks, and nothing changed. With the car fully stock, rolling at 50mph+ in 5th it will climb and overheat repeatedly unless I keep the heat cranked up. Even with no fan at all there should be more than enough airflow at the radiator to keep it cool at that speed.

Today I checked the coolant level/condition and looked at the oil again then started it up in the driveway. I let it get up to about 220 before I switched on the heat and let it cool down a little before I shut it off. At first I thought it was the thermostat because the lower hose stayed cool longer than I thought it would but then I could feel both the hose and radiator were hot. When I pinch the lower hose and rev the engine I can feel the coolant moving.
After it cooled down a little I took it out on the road and it was the same...just double checking.

I'm stumped, clogged radiator maybe? I've done a lot of internal engine work but not much cooling troubleshooting so any help is appreciated.

-Mac


Note: I've previously towed a trailer with three motorcycles, two engines plus other spares and one of those tailgates that sticks up in the wind for hundreds of miles with no heat issues at all.

I would still recommend popping a new (good quality) thermostat on there. Sometimes they are intermittent when they fail. The cheap ones are $6, and the slightly better (GM or Napa/carquest) are $12 i figure, at most. (don't quote me on that)
So, i'd start there, since it's super easy to get to, you only lose a little coolant, and it sounds like it could be that, since at 50mph, it doesn't matter if the fan works or not, it should definitely cool it.

Also, for the fan, my 95 2.2 has had the fan stop working because of the relay in the Engine Fuse Box (it's a square, 4 prong connector) should be labeled. You can buy those relays at most auto parts stores.

Thanks for the info! I'm out of town until after the weekend but pick up a new thermostat at NAPA and a couple of fan relays at a parts yard I'll be near and try those out next week. I didn't have time to check out the fan before I left town so I don't know if it's dead or not but a relay is only going to be like $3 anyway.

-Mac

post up if that fixes it or not....I had a similar problem a while back. but my head gasket had a crack in it between the exaust and water jackets in the block so it was pushing exaust into the coolant making it over heat with none of the normal blown head gasket signs...but I will say just check for bubbling in your resivoir..

I haven't had a change to do this yet and it's going to be another week but I will post back and say whether or not this solved it.

"I'll come back and let you know if it worked" - Famous last words on the internet.

No luck so far. The bleeder nipple snapped so I had to get new heater pipes from a parts yard. I put those pipes in with a new thermostat yesterday and I've still got the same symptoms after bleeding air out until I got water. Now I'm suspecting the water pump could be the problem. I've never had a pump go bad and stop moving water before, only leakers but it seems like that may be the issue here, at least that's the best thing I've come up with.

btw, I did test both the new and the old thermostats in a pan of 180 degree water. Both opened so I don't think the original one was part of the problem....

Basically my theory is that the pump isn't moving much water. I KNOW the thermostat opens at 180-185 but on the car there is no water on the radiator side of the thermostat. I let it run until the temp was close to 200 then kicked on the heater. I'm getting heat out of the core but it doesn't seem at hot as it should be given the water temp so I think I'm getting a trickle instead of good flow.

Anyone else got an idea? It'll be next week before I can work on it again but I've got to get the car going pretty soon.

Any other idea on why the car could be overheating? Time and money are limited so I don't want to just throw a pump at it without reason. Any other ideas why the (known good) thermostat wouldn't be opening once the engine was up to temp? I'll be around the car tomorrow or the next day so I'll see if I can figure anything else out before I get a pump.

Your best bet would be to have a block test done this will tell you if exhaust gases are in the coolant if this is not the case i would suspect the water pump....

ive had the pump itself come apart still spin the pulley but the inside part of the water pump the sprocket wouldnt turn


Erik Packard