Hi there, I'm new to the forum. And I have a problem here with my 4runner witch I love. It is a 4 cyl 2.7L 1997 4runner, I was comming back home from a long trip to texas on my truck, and as I was comming north on I 55 to chicago close to st. Louis I stoped for gas and when I got back in the interstate my temp needle was creeping up this was in st. Louis traffic now. I pulled off the road. I waited it out to cool down, it almost reached the red zone!!!! As soon as I turned it back on the needle was going up again, I turned on the heater full blast and the needle went back to normal operating temperature, its night time now and the weather has cooled down a bit too. I drove all the way back home with the heater on, and the car never overheated like this the rest of the 280 miles. Now here in chicago it drives fine for about 30 mins then the gauge starts creeping up again and I turn the heater on and it come down fast. I need to go back to texas and I need you guys to help me out here. The fan clutch has resistance when I spin it, not too much it spins about less than 1/4 turn when I spin it. The water pump bearing does not make any noise, the check engine light is not on. There is no leaks and the coolant is topped off full. All the hoses are not pinched or bent. anyone knows what can cause this problem. And then cause the temp needle to go down as soon as the heater turns on? Pleade help. Thank you.

 

Stuck thermostat or no thermostat. Clogged Rad core from inside or out. Collapsing hose (only happens under high rpm), Bad fan clutch (but it does nothing at speed anyway) Clogged exhaust/Cat or super lean mixture. Clogged EGR if it has one.

 

A couple of weeks ago I had a check engine light that said burning lean, chamber 1, and the mechanic in texas said it needed a tune up, so he replaced the plugs and wires, etc. That light has not came back on again after it was reseted. And I have driven it back and foward all over the place before this happened with no problems at all. The truck has 100 K miles now. It has a new exhaust system, muffler and cat. I have not checked the thermostat, I'm sure it has one on there because in the cold chicago temp the car reaches opertaing temp pretty fast. And the heat is hot, I have chapped cheecks and lips after driving 5 hours with the heater on.

 

I wonder if the cat is cooked.

 

everything Lars has mentioned is a possible cause-seems too coincidental you threw a code as well. track down each of those.

The last time the coolant was flushed or the timing belt-waterpump replaced.(?) Is it possible the pump is not circulating as it should ?

A common problem on some of the earlier 4cylinders- my old 22re for example- was it needed to be 'burped' properly when coolant and water was being added. If it was filled and not rechecked it would sometimes not have enough volume to achieve proper cooling. I can't recall if it helped to be nose up or nose down but that was one trick I had heard about to achieve full fillup.

Since you have done the exhaust route it seems unlikely the compression is there-my money is on the radiator itself....you should have already done a flush by now at minimum. Using the Toyota red?

The hoses and belts probably done with timing belt? Or -sorry I don't know- does your use a timing chain? Certainly can't hurt to replace those if they are suspect at all. might as well do the thermostat while you are at it...

 

I was looking at tge exhaust last night and found one of two bolts that hold a sensor past the catalyst broken. I extracted the broken bolt and replaced. I tested the truck and after 10 miles / 30 mins the temp needle started rising again. I turned the heater on and the needle went back down to normal temp. I drove it back home.

 

You are trying to troubleshoot a temperature issue here, right? Get yourself a thermometer. That's the tool for the job.

Check block temperature, check radiator inlet temperature, radiator out temp. The cooling system is a very simple system.

 

I'm guess never since its the 2.7 and has a timing chain which is a lifetime item

 

very good that is helpful

so my guess is the water pump is not actually circulating but just impeding water flow. You turn on the heater and that circulates more fluid and the temp drops.

Seem logical? I am no expert but that seems to make some sense to me. I would guess that normally a defective water pump would be making some noise but perhaps yours is not.

So by cost of repair try doing just the thermostat first and try that. If that fails to solve then consider getting at the water pump.

We do give a care and stay in touch so we can learn what it is.

 

How does your oil look? No milkshake right?

 

No milkshake, just oil. I use pennzoil full synthetic 5w 30.

 

Hmm...this is an interesting problem. I'd offer to help but this is one area I'm not too knowledgeable in....so PLEASE keep us posted.

 

Does the 4 cylinder have a egr or maf I've been reading about? Please let me know, if you have a pic or location that would be great! Still have the problem,Thanks!!