98 Overheating and out of ideas

ToddRD · #1 08-20-2010, 05:41 AM

’98, 3.0, manual transmission, 2WD, 138,000 miles with overheating problem. Radiator, radiator cap, and water pump replaced. Hoses appear clear and pressure test holds. No white smoke in exhaust. No evidence of combustion gases in coolant or coolant in oil. Water vanes, body or journals (depending on what you want to call them) in engine block appeared to be clear when water pump removed. Heater core has water transfer evidence by heat being exchanged. Valve in heater line working and appears normal. All other smaller lines checked and OK.
Can run at idle for > 1 hour with AC on and not overheat. When truck is driven down the road the reservoir over fills/pressurizes and blows coolant out the top. If left overnight the coolant returns to radiator. Recent replacement of AC compressor also. Suspect overheating contributed to death of the AC compressor. AC blows cold and heat blows hot (if water is available). One side note is that previous owner used stop leak to the point that lower portion of radiator was clogged up. Never presented an issue until now so may not be part of the problem. Could the fan clutch contribute to this issue? Running out of ideas. Any suggestions welcome. Thanks in advance.

mickblock · #2 08-20-2010, 07:42 AM

Quote:

Originally Posted by ToddRD

Can run at idle for > 1 hour with AC on and not overheat. When truck is driven down the road the reservoir over fills/pressurizes and blows coolant out the top.

That extra stop leak gunk might take up so much room that even if you're putting in the correct capacity of coolant, you're getting this coolant overfilled effect.

Also that amount of stop leak gunk could act as a moving blockage.

Have you done any kind of system flush?

Areyouforcereal? · #3 08-20-2010, 11:45 AM

I would try a system flush. That stop leak crap is bad stuff, and can clog your water passages. An obvious thing that comes to mind is a stuck or possibly installed upside down thermostat.

ToddRD · #4 08-21-2010, 06:09 AM

Forgot to mention multiple flushes and new thermostat. I'm betting on the clutch is bad and can't flow enough air under a load. My wife and son drive in higher RPM ranges and I drive it like I am driving my diesel. I rarely get over 2000 RPM and don't even come close when shifting. They may be out running (heating too quickly) the fan's ability to draw air. A mechanic friend agrees with my theory so that will be the next check. Sometimes it's the simple thing right in front of you that is the problem. Thanks for the suggestions.

mickblock · #5 08-21-2010, 08:07 AM

You think it's running lean?

FireRanger · #6 08-21-2010, 08:33 AM

The fan clutch would be a problem sitting around at idle only. It will have no effect once you're moving. Ram air through the grill moves far more air than your fan does. Those of us with electric fans can shut them off completely once we're on the roll. I virtually guarantee you it is nothing to do with your fan.

Unfortunately, you've also replaced everything else so I don't know what to tell you.