OK. I'm baffled. And a lil pissed.

The beast started over-heating intermittently a couple of months ago, usually only after I had been running it hard and even then it only got warm when I'd shut it down. You could hear the coolant bubbling -- sometimes worse than others, but most of the time it never happened at all. The frequency of these heated episodes became more regular a couple of weeks ago and I noticed that the temp gauge would start to creep into the "warm" range when I wasn't moving, or was in heavy traffic.

Along the way I replaced a slightly leaking/cracked radiator for a larger, brand new 3-core radiator. Problem persisted. My mechanic took a look last week and determined the fan clutch assembly wasn't running regularly and replaced it, too.

He has also been working on putting headers on and fully expected that when he went to give it a test run yesterday that the over-heating issue would be resolved. It wasn't. He the replaced the thermostat; no joy. The water pump is functioning supremely with no difficulty.

So we're stumped. Other than the radiator, water pump, and thermostat, what could be causing the vehicle to have the over-heating symptoms described? I'm entertaining all possibilites at this point.

Ed

 

have you had your head gasket replaced on your 4Runner. I think that 89-95 V6 had a head gasket problem. Toyota fixes the problem for free if it hasn't. You can call toyota @ 1-800-331-4331 and then they can tell you if its been fixed by your vin#.

 

Oh, just to clarify -- the overheating last week blew the damn gasket AGAIN. So he had the heads milled and replaced the gasket. We're still left with the overheating problem that caused the catastrophy in the first place.

Ed

 

what about the Oxygen II sensor? I would also make sure that your air flow is not restricted and your exaust is not restricted.

 

All clear. Replaced O2 sensors (both of 'em; CA emmissions) last fall. All new exhaust, Cat, muffler, and of course, headers as of yesterday.

 

Wow man I have no clue...maybe its that hot Arizona air? When you get your Runner backup and running let me know. I will make a trip out to Lake Havasu. I was there 2 years ago....and damn...one hell of a good time.

 

Replace the thermostat again. I've hear of people buying new ones and them being bad, yes, directly from Toyota. It's worth a shot. Or take the thermostat out completely, and see what happens. This way it's "open" all the time. If it doesn't overheat, you'll know it's the thermostat. If it does, you'll know it's not the thermostat. I assume your fan is in good shape and you're using the shroud right?

 

My thought is also a bad thermostat. Haven't been able to convince him to swap it out again, though. Fan and shroud are in good working order.

I had a thought earlier that my K&N intake might be clogged completely somehow, but that wasn't the problem, either.

 

O2's, intake, etc. have nothing to do with the cooling. Tell your mechanic to use a different thermostat or take it out completely and see if it keeps overheating. If it's been overheating for the past few months, then wer're talking feb/march, and no matter where you are in north america, you really shouldn't be overheating during these months. Something's got to be wrong. If you're confident that he's got the head gasket problem fixed (you're not loosing any coolant are you?) then I would suggest trying the thermostat again, and if that doesn't work, try some "water wetter." But i'd bet it's the thermostat, there's really nothing else it could be unless you've got a bad water pump that isn't circulating correctly.

 

have you replaced your water pump?

 

Is this the 3.0? If the headgasket is in backwards it'll cause overheating. It's very easy to put the HG in backwards and not know it. You can also test the thermostat, rather than buy a new one.

 

FUGGIN MUTHER...SOn OF a...WHY, I OUGHTTA...mutter...mutter...grumble, mutter...

Bingo!

Just got a call from him. He put the damn head gaskets on backwards. Unreal. Looks like one more day driving a loaner.

Thanks for the suggestions, guys.

 

good work robinhood...always to the rescue.

 

What can I say? I like to steal from the rich and give to the poor...

Actually, I'm just regurgating what I've heard from 3 years of being on the boards. Yeah, I'm a web wheeler...

 

Right in time for the summer.

The temperature is starting to creep up here and its no fun running hot, in traffic, in a TOYOTA.

I will see how mines does this summer.

 

That is exactly what was wrong with my 3.4L V6 when I had my engine rebuilt. They put the head gasket on backwards and after they corrected that. The engine ran fine.

 

Wouldn't it be a good idea to have "This side up" written on the head gasket?

Or maybe it already does, I don't know.

 

Been there myself.

 

For the record, running with no thermostat will nearly always overheat. The coolant has to stay in the radiator long enough to shed heat, and removing the obstructive thermostat lets the water flow too fast through the radiator so it's still hot when it returns.

 

That's interesting. Does it do the same thing when the thermostat is stuck open? Also do you have any more pics of your truck flame? It looks great.