Hello I have a 92 lexus es300 with 119,000 miles it has blew the top off 2 radiators. It overheats constanly both driving and sitting its a slow climb even while driving with cap off thermostat housing running reving up will suck coolant down letting off blows it back up im hoping that means my new pump is working. It has new hoses and radiator the cooling fan used to rev up and down now it turns slow enough I can reach down and grab it while running bypassed the filter and did the same I have no air bubbles coming in power steering resivoir but a steady ps fluid flow. When filled with coolant sumtimes will drive for days without overheating sumtimes for weeks no signs of coolant in oil or vice versa noticed tho when adding oil if running car will die if oil fill cap is removed
The engine would stall when the oil filler cap is removed. The drop in vacuum of the manifold due to the cap being opend would cause that.
Do you have coolant losses issues?
Check the coolant level when engine is cold. Top up if necessary. When coolant level is correct, do not run the engine with cap off till coolant heats up as it is going to spill out coolant resulting in air getting into system.