Been having problems with engine #2, probably a blown coolant seal, but maybe not. no white smoke, no steady stream of bubbles, when cranking with fuse pulled coolant flows out of filler neck at an even rate, no geyser, but it overpressurizes the coolant system, blows the coolant into the overflow, and overheats. tried the cheap pour in block sealant, the car was great for 3 days then started to have problems 1 out of every 3 drives. flushed it, tried the heavy duty stuff. fine the first time i drove it, overheated the second fine the third, etc. anyone have any ideas? sorry for the runons, i'm in a hurry. hopefully someone will respond by the time i'm back.

 

Thermostat could cause intermittent problems.

 

Faulty fan clutch could also be intermittent.

 

replaced the thermostat with mazda thermostat many times. the fan clutch wouldn't cause overpressurization, would it? Until I get the white smoke i'm not gonna accept that it's a blown coolant seal