I recently bought a 1990 4Runner with 142K. It was in excellent condition, original owner, all receipts since Day 1, And a complete set of Shop Manuals!
I was prepared for miles of Toyota Trouble Free Ownership!
Not so. At 144K, a coolant leak appeared. It originates from somewhere up against the rear firewall, and also a bit of coolant from the exhaust. Investigation revealed tons of "Stop Leak" in the cooling system.
I cleaned it out and added a fresh batch, which is still holding.
From searching the forums and available info, it looks like a cracked block. This is $5k to $7K to put in a replacement Long Block.
From the forums, it looks like a swap to a 3.4 would be my best option. Has anyone done this? Bought a used 3.4 with ECU and wiring harness, had the adapter made at 4X4 and swapped the engines out? Right now, it is a case of waiting for the sword to drop!
Any assistance or options gratefully acepted. I have happily owned Nissans and was really looking forward to enjoying this Toyota. I am fairly handy with a wrench and could handle the swap myself.
Thanks,
Demi.

 

its probably a Blown head gasket or cracked heads try a search

:pat: good luck Big Kahuna

 

bigKahuna is right!

It's a head gasket or a warped head or a cracked head.

Time to make a call to a local Toyota dealer with your VIN number to see if you head gasket had been replaced. They are still running the special service for replacing 3.0 head gaskets.

And stop using the stop leak. It will ruin the water pump.
Stop leak is a ceramic base sealer that looks for cracks. It also is abbrasive (micro level) and will ruin the water pump and eventally glog the radiator.

There is a company that sells 3.0 to 3.4 conversion gear.
Here's the link click me

Good luck!