So I have noticed in some of the other forums that few owners with the 1UZ vvti or 3UZ are aware that the cooling system runs thru the throttle body to warm it and prevent frost from forming on the throttle blade on a cold day. This is the high point in the cooling system and not the radiator cap like in most vehicles. With this unusual high point it's got a bleeder screw that must be removed and coolant added here and make sure an air is bled out whenever you drain the cooling system. These air pockets can fluctuate as pressure builds and prevent proper circulating in the cooling system. It seems to be a bigger issue in the 4.3 3UZ where it has a unique design flow for the cooling system and this air void can leave you with hot spots that will cause the coolant to boil that's trapped certain pockets and then it's able to escape from the closed system. As it escapes, obviously the problem gets worse. If your not aware of this then it's a good idea to just give your car a check when you have a chance. And verify its full. And hopefully everyone will know how to correctly refill the coolant I the future. Here are some photos showing the bolt on each engine.

Tree His is the 4.0 1UZ, it's the big bolt for an Allen wrenches.

I believe it's this one on the 4.3 3UZ, looks like a 14mm. Let me know if I am incorrect on this into, I don't have access to one at the moment but believe it's the one I the center of these photos.

 

Interesting information. I owned my GS400 for 14 years before I sold it this summer with over 300K miles. During the period I owned the car, whenever I had to replace coolant I would always bleed the cooling system by simply opening the rad cap and burping the system for a short while. Never had any issues. Over the years, I changed water pumps, radiator, timing belts, hoses, even the did some throttle body work and I always did a conventional rad cap bleed when the coolant was refilled. Not saying you are providing false information, just saying I never experienced a problem.

 

I refill the coolant and do the rad cap bleed till it gets warm.

I have a steep hill I use in my yard to pull the car on and hold the rpms up with the rad cap off.

I don't know about any hot spots etc.. I don't know they don't exist though.

 

Same here - My 2UZ has never had any problems in the 10+ years I've owned it by just topping / burping from the radiator after fluid fills. Is this procedure outlined in the FSM?

 

It seems like the issues are mostly with the 3UZ, there has quite a few people with cooling system problems. Either way, they all 1/2/3UZ engines have that bleeder. When looking at the 1UZ in my own vehicle, it would seem that it’s mainly to allow coolant to reach up to the throttle body. Which obviously isn’t critical to have in the system. But for some reason it seems to cause a bigger problem on the newer version, and it’s unique bypass circulation. Just figured I would include anyone with know how to properly refill the coolant.