96 3.4 4runner overheating and stumped
 

So ive searched and searched....for over a week now. Im starting to lose hope.
96 3.4 auto 4X4 - 216k miles.

3 months ago i overheated briefly going up a mtn. Changed thermostat as a precaution and started watching coolant. Noticed coolant was getting low repeatedly with zero leaks and no other overheating episodes. So you know what that means lol. Dreaded milky oil and sweet smelling white smoke out the exhaust was next.

So i changed the head gaskets and got her all back together. Engine runs excellently. Smoother, quieter, and more power than ever before (i bought it a year ago with 203k miles on it). Only one little problem.... It overheats now. Only when driving. Never at idle.
List of things that are new - head gaskets, intake manifold gaskets, knock sensor wire, valve cover gaskets, intake plenum gaskets, tbermostat, water pump, timing belt, added oil to fan clutch, and radiator.

I am just completely stumped. Please help. Thank you.
Eric

UPDATE SOLVED PAGE THREE!!!!!

First thing that comes to mind...if the thermostat doesn't have a 'jiggle' valve, you will need to drill a 1/8" hole in the top of it. Otherwise a pocket of air builds up behind it and it won't open (hot air can't transfer enough heat to open it).

If that's not the problem, check your compression. :great:

When i drill the hole how close to gasket should it be? Thank you.

Just keep it centered, it will be fine.

yeah it sounds to me like you need to bleed the coolant system you have air in there that is just being heated and expanding.

The hole should be about where the jiggle valve is below:

http://img690.imageshack.us/img690/9167/thermostatp.jpg

I would recommend installing an OEM unit since you're gonna be in there anyway. All OEM Toyota thermostats have a jiggle valve and are superior to any aftermarket unit.

Thank you. I had a feeling it might be air trapped in there. I will give this a shot this morning.

One other question. What would be the reason for checking compression? Thanks.

Disregard the compression comment for now...I jumped the gun a little. Start with drilling the thermostat (or installing OEM) and burping the system.

you can start it cooled off and wait for it to warm up , watch the temp guage and when it gets about halfway the t-stat should open .
You can feel the radiator getting warm at the bottom (being careful not to lose fingers) and squeeze the top hose to confirm that coolant is flowing

another way to confirm that coolant is flowing is to turn on the heater , if it is not blowing hot it could be because it is not pumping coolant

sometimes a mystery coolant loss can be explained by a faulty radiator cap that blows off to early

if it is pumping coolant and still overheating , check for plugged exhaust, plugged cats , cooling fan operation , or ignition timing

the fan clutch should engage when the engine warms

when I was a kid in 1971 I got a great deal on a cherry 66 mustang because the guy couldnt figure out why it was overheating, he gave up and sold it cheep , turned out to be that the muffler was filled with sand

Ok so i drilled the hole in thermostat and bled the air out on an incline, 2 big ass rocks i rolled into driveway i drove up on lmao. It is better but still overheating. I now realize that my fan is not increasing speed when the engine starts to get hot. Time for a new one i guess. Anyone have a link for the oem one for less than an arm and a leg? Lol. Thanks for all the great replies. I think i will be sticking around here for a while.

Here where I got my AISIN (OEM) clutch:

http://www.partsgeek.com/catalog/199...an_clutch.html

A healthy fan clutch makes a noticeable roar when started up cold.No roar = bad clutch. If you can stop the fan with a rolled-up magazine or newspaper when hot = bad clutch.

You may find this thread useful:https://www.yotatech.com/forums/f2/1...l#post51509656

I have thought about going to an electric fan, might pick up 5HP ...LOL I might need all the ponies I can scrounge when the snow gets deep:king:

New aisin clutch fan installed....... Still overheating. Now i turn heater on full blast and the temp goes back to normal, but only if heater is on full blast. Im really getting depressed here. Engine runs great and has tons of power. Could a bad lower raditor hose be the culprit?

Check to see it is not collapsing, also check if it is warm. If not warm, then there is no flow through the rad. Partly blocked rad? Or, you just did hg's - there is a thread about installing them left for right, blocking a return to the pump from the engine. Others have found this to be one cause of overheat. Where are you at now?

HEAD GASKET nobody gonna say this?

when they are installed wrong u can blow it quick. i would check your oil make sure theres no water in there. if there is change it all again. also could be something farther internally

I put head gaskets on exactly the way old ones came off. Im pretty sure of that. I just put new lower hose on and old one was really soft compared to new. I need to get some more coolant and bleed the air out, man these things are a pain to bleed lol. No coolant in oil and no white smoke so im fairly confident the hg. are good. However, if this doesnt work i guess i have to tear it all down again and buy another hg and bolts. Real fun being unemployed and going through this......

Were the heads checked by a machine shop for cracks after you overheated it and did the HG job? It could be the HG was installed incorrectly somehow and is blocking a water jacket....

Burping the system is the first thing you need to do. Remember to leave the radiator cap off when doing this. Only once you are certain there is no air remaining should you start looking for other possible causes.

^^ Yes......

enapa, were the heads checked out by a machine shop when you did the HG?