I've been dealing with my Volvo 240 overheating for about a month now. I've gotten rid of the temp compensation board and I just installed a new thermostat. It seems to overheat completely at random but it has been getting more and more common, sometimes I'll drive the car and it'll never climb past the halfway mark, but other times I can't even make it out of my driveway. I'll start the car and let it idle and the temperature gauge just keeps climbing, even with the heat going full blast. I know my coolant levels are good because I topped it off after swapping my thermostat. This is my first project car so I'm no expert, but all I can really think it maybe my water pump is bad? I noticed one of my belts has been squeaking so I thought maybe that had to do with it. Or maybe there's air in the system? If anyone has any suggestions or similar experiences I'd love to hear them, thank you.

 

It takes a few minutes for a engine to heat up past normal range. So if you are saying you start your car from cold and the gauge indicates over normal before you "make it out of my driveway" - there is no way the engine has had a chance to heat up that much. I would suggest buying/using an infrared thermometer to determine the approximate temp of the engine when the gauge indicates too high for your comfort.

Have you checked the insulation on the wire to the temp sender under the manifold - commonly the wire makes contact with others in the harness giving a false temp reading - you might want to substitute a new wire from the sender to the gauge at least temporarily until you are sure there's not a problem with the engine wiring harness.

I once had a car with an erratic temp gauge - every time the customer came in we would try something new. Nothing fixed it - temp comp, new wire, replace sensor, scratch head - Eventually the spark plug wires needed replacing and miraculously the gauge was once again accurate.

The water pump is just an agitator - and I've never seen an impeller come off (on a b21/23/230) . That's not to say you might have some sort of crappy aftermarket pump installed where the agitator did fall off - but I doubt it.

 

It normally takes about 10 minutes of idling for it to get right below the red zone, does that seem like too little time? I was planning on getting a thermometer next to make sure the engine is actually overheating, it's never boiled and I've never had the engine start steaming on me, so I've always been a bit suspicious of that. The only reason why I'm still afraid it might actually be overheating is because it stalled out on me one day before work waiting in the parking lot. I had the a/c running and I was sitting there for a while and I looked up and saw my temp gauge was just below the red, then the engine stalled out. That was around the middle of January, but I haven't had anything like that since.