1990 overheating

[abunaitoo]

1990 4 runner. V6, 5 speed.
280,000+miles.
It overheats at different times.
Sometimes when driving. Sometimes when idling. Sometimes when driving slow. Sometimes when on freeway.
Thing is it dosen't do it all the time.
It can go weeks and not overheat.
Waterpump less than a year old. Radiator about three years old. New cap and thermostat. Antifreeze.
Fan clutch feels good. Suck through the radiator.
Pressure test is good. No leaks.
No white smoke. No white coolant. No bubbles in radiator.
Engine runs smooth. Good power.
Don't find any vaccum leaks.
Last time it happened, just drove 20mi freeway speed. Drove in moderate traffic for about 5mi. While in drive through of McDonalds, gauge started to rise. Parked and turned off engine. Gurgling. Let it cool down. Added 1/2gal to radiator.
Any ideas?????

 

[KidVermicious]

What's your compression look like? If you're having to add coolant it's gotta be going somewhere.

 

[nicnmike]

Have you owned this vehicle since new? Maybe someone used a head gasket leak sealer in it and it's clogging some of the passageways.

 

[abunaitoo]

Not my 4Runner

It's not myines. Just helping a friend.
It is overheating. not only does the gauge show hot, but you can hear the coolant gurgling and steam is coming out of the overflow bottle.
Probably need to add coolant when it cools down, because some of it has boiled out of the overflow.
Pressure tested the system. No leaks.
Need to do a compression test. But engine runs smooth, no smoke and good power.
I'm sure compression is low. But probably even.
This dosen't happen all the time.
It could go for a few days to a week before it overheats again.
Strange one.

 

[Robmills72]

Check the radiator cap seal. I had the same problem because the coolant was boiling and the steam would come through the cap seal leaving me with little to no coolant. This happened last summer and believe me, you don't wanna have a truck that over heats when it's already hot out

 

[abunaitoo]

Cap replaced

When I pressured checked for leaks, I also checked the cap.
It was leaking, so a new one was installed.
We thought that was the problem. But it boiled over again later that same night.
He called me today to give a report.
All normal. No problem.
Strange.