I have a 2006 Suzuki Forenza with about 53,000 miles on it. I blew my head gasket in January and after a bunch of repairs, the mechanic put in a new engine. From what I have been told, just about everything under my hood has been replaced. The engine, radiator, water pump, thermostat, hoses, timing belt, serpentine belt, and pressure cap.
After having my car back for a couple days, running fine, the temp gauge needle started to slowly move up toward the H, it only got to about the 3/4 mark, and I turned the heater on and went straight the the shop. They looked at it, the fluids were full, and there was nothing apparently wrong. One of the mechanics test drove it, and drove it hard (I don't know what speeds or RPM's) and the gauge stayed at the middle mark. This morning, I took it for a drive. It warmed up slowly (in a normal fashion) and I took it out where I could get some speed. I hit about 60 mph and after a minute or so, the needle started going up again. I turned my heater on and the needle slowly went back to the middle. I continued driving, turned the heater off and the needle stayed in the middle. I turned on the AC and got to about 70-80 mph and the needle stayed steady at the halfway mark. I am at a loss, I have no car experience, and everything I know has been told to me by my mechanic. I am so paranoid, and I want to be able to rely on my car. Any ideas what could be wrong when everything has been replaced already? Thanks