VB2NER

guess we'll find out, i'll post the results of a new thermostat laster today...

Fabrik8

Many cars have a separate coolant temp switch for the fans, and that is independent of the coolant temp sensor. That's totally beside the point, but keep that in mind if while you're troubleshooting.

So after you've checked and ruled out the likely suspects, and the problem still persists:
If the thermostat is good, the water pump is good, and the fans are turning on, it's possible that you have a clogged radiator. It happens, and your car is 17 years old so it's possible. A coolant system flush may help, but it's usually a waste of money unless you know you have a problem (obviously).
I'm going to have to agree with the water pump or thermostat diagnosis though, those are the two main players when it comes to this problem. Thermostats are usually easy to replace, and even a partial failure can cause the problem you're talking about. That's usually the first thing I do when checking coolant system problems because they're so cheap and easy to do, and should be replaced every few years anyway so stuff like this doesn't pop up while you're on vacation or something.

VB2NER

Fabrik8, thank you for the thorough analysis. I appreciate it dude

I was thinking, if it is the water pump, then the car would just heat up and just keep heating up till it overheats, right? My car never overheats to the point it goes into the red. Actually this only happens every now and then, like at random times. So i am thinking it must be the thermostat just getting stuck, or like fabrik8 said, a clogged radiator. I picked up the thermostat from bap geon a few minutes ago, but can't pick up the gasket set till tomorrow, so i will replace it first chance i get and let you know what happens

BAD4DR

They usually break one post off, and stay in a partially open state. This causes it not to slow the flow down properly, and it doesn't cool as it passes through the radiator. It would usually tend to run somewhat hot that way.

That's also a symptom of eroded blades on a water pump. Higher speeds produce additional flow, and it balances out a bit on cooling. Extended periods of idling (with the reduced flow) would tend to show higher temps, and it would take some time for the temps to come down as you drive, as the flow doesn't push enough hot water out of the block and back into the radiator. Worse, the engine is operating at higher speeds, and generating more heat, so it may or may not come back down.

I do find it interesting that manufacturers would go through the trouble/cost of adding an additional sensor, rather than using the modern CAN/BUS style system to read the one sensor, and tell it to cut the fans on. Seems a bit ridiculous honestly. But then again, it's a little more idiot proof that way I guess.

Naptime

You be at my house early sat morning and lets fix the fucker, then get your n3w volvo . No awnser on the wheels yet man, I'm gonna keep try'n.

VB2NER

i wish i had the gasket, i would just throw it in right now. I can't wait to get the volvo It is just taking forever...

ALSO, i drove the car for quite a bit, it started getting hot. I got home, and just sat in the driveway for like 10 minutes, and it never heated up the entire time it sat at idle. I will be sooo pissed if i have to replace the water pump

Fabrik8

They're just a cheap bimetallic thermostat-type switch, totally passive. Much less sophisticated than a thermister based coolant temp sensor. Temp switches are pretty reliable, so I guess they bank on that. THere is probably some other reason that I'm overlooking..
I agree though, I'd just use the coolant temp sensor to activate the fans right from the ECU if I were designing it. Many cars are doing it that way now.

VB2NER

I forgot to mention that my coolant level has not changed at all, if it were the waterpump wouldn't it leak? Or if the blades are worn it would't leak?

VB2NER

found this on probetalk.com It explains my situation perfectly, but of coarse, no one replied to this thread:





odd overheating issue

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normally the car runs like a champ...no over heating issues or anything.

Recently, I've noticed that it likes to run warmer than normal. Can happen in town or on the highway but normally it's after the car has been run for a while. The temp guage just starts to creep up. I can put the heat on full blast or actually turn on the AC to run the aux. fan and that usually brings the temp back down. Sometimes it stays down and other times it will creep back up.

Coolant level is good and w/p and t-stat are all newer.

Any thoughts? I'm thinking maybe coolant flush...maybe some gunk got loose and is in the system.

Fabrik8

Interesting. How does the radiator look from the outside, is it really corroded or anything? This may just be radiator scale inside the cooling tubes.