DubJunkE

Can't figure this one out. My 90 4Runner 3.0 keeps overheating it's not the headgaskets I just replaced them when I put new heads on the Runner. The Thermostat is new, the fan is new, Im not sure what else is going on here.
The only thing I can think of is I broke a connector that attaches to the housing on the back of the motor with like 4 other sensors on it it's one of the connectors with two wires on it would that affect the colling though?

Give me some input thanks
Oh yeah the motor never overheated before the new heads.

jimbo74

waterpump? electric fan or clutch drive?

dont keep driving it, even 1 time overheating is enough to fry the headgaskets no matter how new they are.....

DubJunkE

Clutch driven fan fan clutch is new too, not sure on the waterpump I think it's working how can I verify this?
I haven't been driving it just testing it out in the neighborhood and parking if it starts to heat up.

ChickenLover

You might have put the headgaskets on upside-down (a pretty common mistake). You are still running the fan shroud with the new fan, correct?

Edit: Are you sure your cams are timed correctly? Ignition timing as well?

Steveh29

I was going to say headgaskets upside down too. There's a tiny hole drilled in one end and they can't go on backwards or you'll overheat. Feel the back of the engine block where the head meets the block. If the headgasket is sticking out, that's the problem.

DubJunkE

I believe the HG's are in correctly they don't look like they're sticking out. I am still using the fan shroud.

The cams are timed correctly I believe but the ignition may be a little off it's got sort of a rough idle like it's missing but would that cause it to overheat though?

Steveh29

If the ignition timing is off it can cause overheating. As can running too lean.

2ToyGuy

The water pump can be verified easily by leaving the radiator cap off when first starting and watch the water. When the thermostat opens, the water shold start going by pretty fast. If not, maybe the water pump is bad. Probably, even. Also, check for water coming out of the seep hole under the shaft coming out of the water pump. If it is, your pump is definately bad.
Is the radiator good? Is the entire surface hot after the truck warms up? If there are cold spots, the radiator cores are clogged. You'll need to either get it rodded out, or just replace the radiator.
Did you "burp" the cooling system after you put teh new heads on? Sometimes with new heads, you need to really work to get all the air out. Best way is to get teh front end as high as possible relative to the rest of the truck, and then start it up with the readiator cap off. Once the thermostat opens, most of the air should migrate to the radiator cap, as it's the highest point in the cooling system. Once the air is out, put the cap back on, and shut it down. Make sure there's plenty of coolant in the recovery tank. Start it and let it warm up real good, stop it and let it cool completely a few times to make sure you get all the air out.
Also, a good water wetter can make a huge difference. It lowers the surface tension of the water, ensuring a better coating of the interior parts with water, thus better cooling.
And yes, timing can make a huge difference in overheating. Make sure the timing is right on per the FSM.
Just a couple of ideas from a guy who's been through all this in a place where the coooling system is absolutely critical. 115* in the shade is hard on cooling systems. I have to have mine peaked to max performance or it can overheat easily...