I’ve got a 1992 240sx convertible... automatic. Runs great. Several days ago I noticed that my AC suddenly didn’t feel quite as cold. Shortly after I noticed the dreaded steam blowing up from the front passenger side of the engine compartment where the coolant overflow reservoir is. The thermostat gauge on the dash was at the normal operating mark. I pulled over to check it out and noticed the coolant appeared to be boiling/bubbling in the overflow tank. It didn’t take long before it settled down.
I decided to replace the radiator cap first. I drove the car a few days without any issue after doing this. Then I noticed the AC struggle to get cold. Again the steam began blowing up. Temp gauge on dash was still fine. So I flipped to full heat blasting and drove home with the windows down. The steam subsided before I got home. I could see coolant had bubbled out of the overflow stem.
I checked coolant and it was low about 1 quart... I assume from bubbling out. After topping off I drove it again. Same problem. It seems if I run the heat full blast the issue isn’t as noticeable.
I was nervous about a possible blown head gasket because the coolant looked murky. I did a coolant system pressure test. It held strong. Also, my oil in the engine looked great. So I don’t see that as the culprit (thank goodness... unless I’m missing something here).
I drained the coolant and added new coolant. Burped the system. Took it for a drive and sigh... coolant had backed up into the overflow tank again and was bubbling. AC won’t blow cold at all. Engine temp according to dash gauge is great.
I don’t see any leakage from the water pump which I guess could be a possible culprit. Anyone have thoughts on this fiasco?