quick 7M question, albeit i know the headgasket issue has been beaten to death
ive got a 1991 Crown with 7MGE, 93,000km. a few weeks ago i took it on the highway. 2 hour round trip, went about 160kmh at 4000rpm the whole way. after i got home, the coolant reservoir was empty and the rad was half full.
i thought the valve in the rad cap maybe went bad and stuck open causing coolant to blow out the reservoir, old cap was from when the car was in Tokyo so around 10 years old. put a new cap and thermostat in, went on the same highway last week going 170kmh there and when i got there, the reservoir was full of coolant, overflowed coolant allover the frame, and the rad was down about a quarter liter. so i filled it up again before i went home. when i went home i drove only 130kmh, lost no coolant from the radiator and the reservoir never overflowed and the level stayed in the correct area
car doesnt overheat ever, only floods the reservoir if i go faster than 150kmh. no leaks, oil is clean, blows a bit of white exhaust only on cold starts but no sweet smell, pulls fine all the way to redline. im at a loss, only thing i can think of is the headgasket is just starting to go and combustion gas when i go that fast is flooding coolant into the reservoir. plausible or could it be something else? knowing 7Ms i keep jumping to it being the headgaket