I have an '88 Yota 4x4 180,000 miles. I bought the truck at 169k. Shortly after I bought it, the timing cover blew due to worn timing guides and chain rub. Caught it fairly quickly, replaced all timing components and timing cover. Two weeks later I had coolant in the oil again. Blown headgasket. Replaced the headgasket. By the way, I have replaced the thermostat, water pump, fan clutch all within the last month. I replaced the radiator with a brand new one last year. I took the thermostat out because I though it might be faulty. I checked the timing and it is perfect at 5btdc.
I cannot get it to stay cool. It stays cool at idle, but will not cool at rpm, especially on a grade on the freeway. The engine runs very well, has power, uses no oil, and has no coolent loss. Please help me. Any suggestions??????? :wtf:

 

did you check your radiator hoses when it does overheat?? are you sure its circulating efficiently??

 

I have looked at all the hoses. No signs of leakage. As far as circulation, I am not sure how I would assess that. It has all new cooling components includin water pump and 1 year old radiator.
Could a cracked head result in overheating without any coolant loss or loss of power? Thanks. PLD15

 

Perhaps it's running too lean? This can casue the temp to go up but probably not as much as you're seeing. You know, that engine was not meant to run on moonshine...right?

 

A stretch, but did you back-flush the A/C condensor fins with water before you installed the new radiator? It may have so much crud in it after 190,000 miles that it's not allowing enough air through to cool the radiator.

 

Thanks for the input, unfortunately, my truck has no A/C and no power steering from the factory. It is a bare bones EFI 4x4.

 

I don't know if this would apply or not, but on some older LC's the manual called for 20W50 oil and wouldn't cool properly running on 10W30.

 

i mean when its up to temp or overheating are the top and bottom radiator hoes hot or is one hot and one cold, etc....

 

On the hoses issue, when the engine is hot and you rev your engine, is a hose pinching together from the suction causing restricted coolant flow? I had that happen on my 77 Corolla that I used to have.

You mention your radiator is brand new. I assume you mean brand spankin new but I will comment anyway. If it was replaced from another vehicle, it may be stopped up, but I think it would tend to overheat more at idle if this was the case.

Hope you figure it out.

 

These are not hot running engines, and are not prone to overheating.

While in the driveway:

Pull off your radiator cap and observe fluid flow. You should be seeing it flowing across the opening when the engine is warm and the thermostat is open.

Now rev the engine by hand and observe the flow. It should substantially increase, even gush out some. The increase in flow should continue. While holding it revved up, look for a collapsing of the lower radiator hose.

Be aware, there are two lower radiator hoses, and the hidden one almost never is replaced. This one can be the one failing and collapsing. You've got to go under the truck to find it. The metal pipe where the 1st radiator hose connects ends shortly and there is a second rubber hose going up to the water pump.