I have a 1995 Toyota 4Runner 3.0 that overheats when it starts to drive. We can be working on the car for over 30mins to a hour not over heating, but when we drive it around the neighborhood it overheats. I’ve changed the radiator twice, got a oem t-stat,recently put a new water pump. Solved my other heating issue for a bit. new upper hose, new fan clutch, fan and shroud I even flushed the system about 10 times now. There are no leaks and no more rust stuck in the system. No white smoke coming from exhaust or oil and coolant mixture . I’m using a 50/50 mix coolant. Could it have something to do with the transmission??

 

If you've checked all the boxes for the status of the cooling system could it be the temp gauge? Could go pickup one of the cheap laser thermometers and see what the temp of the rad is when your gauge says it's overheating.

Air in your cooling system will also causing the temp to bump up suddenly but I would expect that to happen at idle too not just when driving.

 

Any other suggestions

 

Once it cools down pop the radiator cap off. Then fire the truck up and watch the coolant. It should sit still then when the temp gauge hits warmed up temp, the T-stat should open and you should see coolant flowing. At least this would help eliminate the T-stat. They have a little bypass hole and at idle it will move enough to keep the vehicle cool. But if it does not open and you start driving around then that is more than enough to boil it over.

Jake