Cruiser Overheats...again

[MRDeadhead]

My GF's '01 Cruiser Touring overheated last night in stop and go traffic...added antifreeze and checked it today. After running it for 15 minutes, it overheated and blew cold air thru the heater ducts...even though it was set on "HOT". However, the heater did blow hot air once the Cruiser warmed up...but only until it overheated. Once it overheated, the air was cold. There aren't any puddles on the ground and there's no evidence of antifreeze leaking in the engine bay. My guess is that the thermostat isn't opening correctly...if at all. There was no visible coolant in the thermostat housing (after removing the cap)...I could see the thermostat itself. Any ideas?

[NCPTCruiser]

I suspect a faulty heater core...do you smell coolant? (a sweet smell)

[2step]

It could be that the coolent was quite low in the first place and you haven't added enough. The heater not working is a sign of the coolent being low.

If you added coolent without the engine running and everything being warmed up with the thermostat being open, then you haven't displaced all the air in the system. Let the car run for a while, with the cap off, until it's near operating temp and the waterpump is circulating the coolent and then top it off. That way the air and steam will all be pushed out and coolent can be filled to the proper level. The fresh coolent needs to be slowly blended into hot stuff so as not to cold shock any hot engine parts and cause them to crack.

Also pour additional coolent in the overflow resevour because the coolent will shrink and contract as it cools and pull the extra from the resevour instead of pulling air.

Be very careful opening the radiator cap when the coolent is hot. It can immediatly turn to high pressure steam and burn you badly. It can be done if you are careful to insulate your hand with something like a large towel and you only turn the cap to the first detent. The towel should be generous enough to screen all bystanders from jets of hot steam. The hot steam has to go somewhere and if not on you then all over your engine. I don't recommend that anyone try this unless they really understand the forces they are dealing with.

I don't know why your girlfriend's coolent got low to start with. It may be a problem but it's common to just be able to top it off and your done.

[MRDeadhead]

I can smell the coolant when the heater is on, but not when it's off. I replaced the thermostat and the rad cap, and it still overheats. I took it for a test run (15 minutes), and it was blowing cool air through the vents and it was releasing steam from the rad cap.

[NCPTCruiser]

I still think this sounds like a bad heater core...

[MRDeadhead]

We're going to try the "flush-n-fill" tomorrow and then we'll try the heater core after that. The f-n-f will be a little cheaper (and less complicated) than the heater core...so hopefully that will work. I'm sure that the heater core is quite a labor intensive task. Last time I did one was on a '72 Dodge Dart...and that was royal pain in the a$$. Cross your fingers for the f-n-f...mine are.

[NCPTCruiser]

Good luck! Keep us posted!

[QuicksilverDon]

I can't see a heater core causing overheating, unless it's leaking and lowering coolant level. I think the heater core is a symptom - probably air in the system.
How many miles? Overheating can be water pump, thermostat, leaking coolant, engine fan not coming on, or head gasket.
You've done thermostat, and F-&-F is a good next step. Hopefully, where you take it for F&F will refill it properly and get air out, then see if overheating returns.
How does coolant look? Clear? Oil okay? Any sign of coolant leaks?

[alanrw]

Remember, these cars have a bleeder screw right by the thermostat housing. You can't bleed all the air out of the system by opening the rad cap alone, you have to loosen the screw and let the air out. Be careful, you are dealing with warm coolant.

alan

[MRDeadhead]

Here's the lowdown. I replaced the thermostat...no difference. I replaced the radiator cap...no help. Flushed and refilled with new coolant...no help. Replaced the water pump...bingo! Apparently, when these water pumps go bad, the shaft spins inside the {plastic} impeller and it doesn't circulate the coolant. When they are cold, the shaft spins the impeller...but once it's warm, the shaft spins INSIDE the impeller since the plastic expands more than the steel shaft. Hence the feverish croozr. As for the on/off warm/cool air thru the heater, don't know about that one. The heat is fine now...can't understand how the temperature of the heater air would drop that quickly. But as long as it's working, I'm not too concerned. Now if I could only figure out why the oil pressure on my Jeep Wrangler gauge is pegged at 80 psi, I'd rest a lot easier. Thanks to all who aided in my dilemma...you're good people!