Strange 4.0L Overheating Issue

Hey folks, hoping you guys can help me out:

Trying to help my sister out and I've been having some difficulty finding information on the topic. She just picked up a 2004 Toyota 4Runner Sport Edition, 4.0L, automatic, does have some some oversized tires on it, (285/70R17) and it has roughly 204,000 miles on it...

She's only had it for 2 days now, got a great deal on it and its fairly clean. She asked me to check out the rig, knowing I'm a Toyota enthusiast. I figured I could help out, so I got behind the wheel today and put it to the test. Foot to the floor, cruise control, heat/air conditioning, everything seemed great! Until...

She hopped into the driver's seat and I jumped back into my Tacoma, and we headed for a local trail. It's a long, paved, and uphill climb to the dirt. Once we hit the dirt, she switched the 4Runner into 4WD high, and we drove about 200 yards before I started to smell it overheating. We stopped and while we were sitting there deciding what to do, I watched the engine temperature climb almost to the red zone.

We decided to head back, and as soon as she took the 4Runner out of 4WD the temp started falling. By the time we hit pavement, it was back to normal and drove for the rest of the day at normal operating temperature.



Diagnosing the issue:

• I noticed the reservoir was almost full to the brim.

• The fan clutch was working properly, did the magazine test.

• Neither the top hose or the bottom hose had any pressure at all.

• No leaks from the radiator, any of the hoses, or the motor.

• Replaced the radiator cap, no resolve from doing so.

My thoughts:

• Maybe a stuck thermostat? Since there's no coolant flowing from the engine to the radiator.

• I don't think its a clogged up radiator, I was had squeezed the lower hose and got fluid to go into the upper hose.

• Maybe a bad water pump? They're a known issue apparently.

Anyways, hoping somebody has had some experience with a similar overheating issue with the 4.0L. Anything helps guys, and thank you in advance for your input!

 

Could be a Blown head gasket I would have it checked out if it hasn’t had the gasket done they all do it those years unfortunately 04-06 mainly but can go up even higher in the years

 

sounds like a blown head gasket

 

Maybe try some a/c condenser foam, spray the radiator let it sit then spray it out with water. Might be that simple.

 

If you have coolant, try the thermostat first. If the rad hoses don't get hot when getting up to operating temps its either clogged or at least not flowing at full chooch. You can test your coolant for head gasket leaks or smell the exhaust for a sweet smell (if its small you won't notice and will have to test the coolant). You can try to check the pump by taking off the cap when cold and start it and look for movement in the coolant.

 

If it went 16 years without overheating, there’s a definite cause. My 04 needed a new radiator. I’d advise to track down the problem and have it resolved properly.

Water pump is cheap, so is a radiator and thermostat.