overheating

[sk]

2004 explorer with 200+ grand miles on it. Have this overheating issue that is perplexing not just me but two of the mechanics I know as well. Have tried everything that I know short of rebuilding the top end.
Here's the situation:
Started overheating out of the blue. Had the water pump, thermostat and sensor all changed. Brand new stuff. Even got a different thermo because I thought the new one was bad. Still overheating. No water in the oil, no moisture in the tail pipe. Discovered the fan clutch was bad so I changed that out. Still overheating. Was thinking I had a bad head or that the head gasket was bad. Took it to a friend who is a mechanic to look at it because a head swap is beyond my scope. He didn't think it was that so he ran a few tests. Put some stuff in it that is supposed to change colors if there is an issue but it did not. Took the rad out and took it down to the local rad shop and they cleaned it out and re-rodded it. Got a crap load of nasty looking stuff out of the rad. Literally a softball size ball of crap. Took it for a test drive today and drove all over town with zero problem. AC working fine and no overheating issue after stop and go in the city for at least 30 mile in 93 degree weather. Got on the interstate and up to 80 mph. Drove for about 2 1/2 miles and BAM! Over heating issue again. Maybe the gauge is bad? Going right now to by a mechanical gauge to see if that might be the issue. No real noise from the engine and it actually seems to be running fine with the exception that the gauge is reading hot and the idiot light is on. Any suggestions would be appreciated.

 

[X-LION]

Try taking a look at your air intake manifold. I have been experiencing coolant lost but nothing was visible and overheating was fluctuating. Change the manifold and the truck was good to go.

 

[sk]

Air intake and filter is fine. I did check that earlier but forgot to mention it. Trying a mechanical gauge and flushing the system as we speak. Thanks for the input.

 

[X-LION]

Do you have coolant loss?

 

[sk]

No coolant loss

 

[pet575]

He didn't say "air intake" as in the box where the filter sits. He is talking about the entire intake manifold. Only way to verify that thing is "OK" is to remove and inspect the entire manifold.

Have you put an IR temp gauge on the motor when it is overheating to verify that the gauge is working correctly?

Also, I had this happen on another vehicle and I was completely baffled. Turned out the degas bottle cap was bad and wouldn't seal correctly.

 

[sk]

I actually have a temp gauge on it now and it goes up to just under 210 for a minute or two and then back down to 190 and stays there at idle. Haven't test driven it yet because I just discovered that the new clutch fan I had put in is bad. About to take that out and return it.
When you say the degas bottle cap, what are you talking about?

 

[pet575]

The cap on the bottle that holds the coolant. In the old day's we'd have called it a radiator cap because it was actually on the radiator.

 

[Joe in NY]

210* is not really overheating... GM has all of their motors running at 210* I would start to worry at 230* for real overheating. But temp outside of normal operating temp is never good.

 

[Bobmbx]

I actually have a temp gauge on it now and it goes up to just under 210 for a minute or two and then back down to 190 and stays there at idle. Haven't test driven it yet because I just discovered that the new clutch fan I had put in is bad. About to take that out and return it.
When you say the degas bottle cap, what are you talking about?

It does this while you're idling? Temp up then down? Any fan speed, idle speed increases or other sounds associated with the temp swing?

What is your idle speed? Try increasing RPMs to 2k and see if the temp fluctuates at the higher engine speed.

It sounds like your thermostat is opening late. Are you positive its not installed backwards, and that its the right one for your vehicle?

 

[sk]

Yes. It does this while at idle at this point. It seems to have a mind of its own to be honest. Yesterday, it went up to 210 and then back down to 190 initially. Then later on after I changed the fan clutch (again) it went up to 225 and continued to climb. All at an idle. We tested the thermostat and it is working fine and it is installed properly. I have not yet taken the manifold off to check that because that is beyond my scope and I am trying everything I can before I take it somewhere to get something like that done.
Pet575, I have a brand new bottle cap because I did think of that and it's working fine. Thanks for the explanation. I'm old school and still call them rad caps.

 

[wingcmdr]

Mine just started overheating this morning, jumped to 244*, it's got a radiator leak but has water in it, the leak is intermittent, it dumps water once a week or so, like a steady stream from under the truck dumping. Mine is a 97 merc v8. it's got a new water pump already.