'88 4runner overheating on freeway only(I'm puzzled)

[Rob92083]

I have an '88 4runner(3.0L V-6) that is having overheating issues after driving extended periods on the freeway. I just recently bought the truck from a lady who had it just sitting for about two years and have replaced the water pump, t-stat, most of the hoses, timing belt, plugs, wires, cap&rotor, and all fluids(have not yet replaced the radiator). The truck runs great other than having to turn on the heater while driving on the freeway for extended periods. Any suggestions/help would be much appreciated. Thx.

[jetwhine]

Rob92083,

Did your rig overheat before you did all that work or after? If it did before, I would check the compression on the #6 cylinder to see how the health is on that cylinder. The #6 is the one that has head gasket issues on the V-6 3.0 liter.

[Rob92083]

I didn't even attempt any major trips before I did the work. It was in dire need of some attention. The fluid in the radiator was like a rust colored mud. Also on top of all the other stuff, I did flush the block/radiator(several times)and now the fluid is a nice green. It's wierd it only gets hot on the freeway. The truck drives fine in four-wheel drive, with the a/c on, offroad, all day long out in the desert in one hundred degree heat. Darn thing just hates these crazy California freeways....

[Rob92083]

To comment on the latter of what you said about the cylinder. It does leak oil somewhere in that general area....I've got nothin' better to do on my day off...So, looks like a compression check is in order...

[jetwhine]

Rob92083,

You know it almost sounds like your thermostat is not opening all the way. That is maybe why at slow speeds it operates normally, but when on the freeway it is not open enough to allow proper cooling. I would take it out and put it on the stove and heat some water and watch to see if it opens all the way. I bet it is bad and is not uncommon for this to happen with a new t-stat. I have seen may new ones fail right out of the box. I would look into that before you do anything else.

[Rob92083]

Well that's too bad you probably know what a pain it is to get to those t-stats, but it sure beats losing the motor...I appreciate your time...thanks again...