I don't know what the issue is.

[Mordekai]

Greetings,

Bear with me. Last summer my 04 V6 Limited 240k miles started to overheat at idle. After two previous shops diagnosed a head gasket a 3rd shop....getting ahead of myself here.

Engine would over heat, Recirc light would come on, ramping the heater and upping the RPM appeared to help coolant flow (audible slosh from the firewall). At consistent RPM (highway driving) no issues, but once I get to city driving it starts to get dicey. Have to throw to neutral and get the RPM up insanely high (basically redlining the RPM). This is the 'trick' I have discovered to keep going while I have been working with the shop.

First shop replaced my water pump and cooling fan. They said the fan was loose and the wobbling of the fan damaged the pump. Cool. Had them do the repair. Issue persists. They tell me then it's probably the Head gasket. I needed time to decide, so I took it home and debated the cost.

Decided to get a second opinion, so I took it to a Toyota 'Specialist' They had it for a week and quoted me a ridiculous amount. I was suspicious, because they couldn't give me any real test results (Leak-Down, UV, Carbon Test, Etc). They would later call me (maybe 2 weeks ago) and tell me they made that quote because they didn't really want to do the job...

Third shop: Take it in tell them all the previous and they want to do their own testing. No worries, I re-test any computer that has been previously diagnosed, I get it. They call me back after only a few hours. Radiator and lower hose. Had them replace and flush the system. Everything is golden...for a while. The issue has returned for some reason. Coolant in the overflow looks good and levels are stable. I am thinking either of the following, but want some advice:

1. Thermostat
2. Heater Core

Thoughts?

 

[Bleu62]

Have you looked at your coolant? Is it red/green or whatever color it’s supposed to be? If it’s discolored I would do the recommended flush and replace thermostat regardless.
When your 4Runner is cold and you start it does the coolant temp in the dash slowly get warmer or go from fairly cool to hot family quickly, it may be cool for a while before your tstat opens? If it warms slowly from cool that indicates the thermostat isn’t working as it should.
Does your engine oil look good, or like a milkshake? Do you have white steamy exhaust? Are you losing coolant or it’s just not cooling your engine? Just wondering where they are determining the head gasket.
Sorry to hit you up with so many more questions.

 

[MT Runner]

I had a similar situation. Didn’t have to redline it, but definitely had to get it up to about 2000rpms to keep the temp down while stopped at a light, drive through, etc.

Mine ended up being the thermostat housing. The other possibility on mine according to the mechanic before we figured it out for sure was the fan clutch.

Those are my two semi-educated guesses.

 

[Mordekai]

Have you looked at your coolant? Is it red/green or whatever color it’s supposed to be? If it’s discolored I would do the recommended flush and replace thermostat regardless.
When your 4Runner is cold and you start it does the coolant temp in the dash slowly get warmer or go from fairly cool to hot family quickly, it may be cool for a while before your tstat opens? If it warms slowly from cool that indicates the thermostat isn’t working as it should.
Does your engine oil look good, or like a milkshake? Do you have white steamy exhaust? Are you losing coolant or it’s just not cooling your engine? Just wondering where they are determining the head gasket.
Sorry to hit you up with so many more questions.

Coolant is red and the oil looks like oil. The temp gauge does slowly climb to what I will call 'Normal' (basically the center of the guage). As I said two shops I don't even think did testing and the most recent shop did the tests and showed me the results. I bought a new thermostat which I plan to install this afternoon. Fingers crossed it works.

 

[earthrealm]

From experience, likely culprits.
1. bad radiator cap
2. pin hole leak on any of the radiator hoses that only leaks when hot and pressurized
3. weak fan clutch
4. faulty thermostat --- didnt see if you have changed it