2002 KZN165 since new only 230K on ODO
The radiator is retaining pressure overnight i.e the coolant overflow bottle is filling up over a period could be days but also depends how long its driven on the hi way if I do 500ks it will get to 3/4 full and not return to the radiator as it cools down as it is supposed to.
Cap replaced with Toyota Genuine no change.
When the engine is cold overnight and turn the cap 1/4 turn to the first stop when removing it will vent air into the bottle i.e blow a few bubbles.
Never been overheated owned since new and only driver.
Temp Gauge sits at near horizontal and has not moved in 20 years.
No water in the oil.
Does not use water as i just remove the bottle pour it back into fill the radiator to full and the bottle will then be close to the full line of coolant.
Noticed it 18 months ago but should do something about it.
So I assume a gas leak into the water jacket somewhere which could be Head Gasket, or a crack in the head or Block, Water pump?
any pointers appreciated and what to do first?