I have a 2005 Honda Civic automatic transmission with only 43,000 miles on it. Whenever I come off the highway the thermostat gauge needle starts rising almost to the H. I usually just turn the heater on high to bring it back to normal until I get to a parking lot and let it sit. I took it to Honda who did a pressure check and found no leaks. They did however, put in a new fan relay. When the problem was not solved, I had the radiator flushed and the lower hose and thermostat replaced by my mechanic. About a week later I took it on the highway again and the same thing happened.
When I get home, I usually wait for the engine to cool and check the coolant level in the radiator since the overflow tank is always full. Since I can usually see the tank holes in the radiator, I fill it up to the neck. I have checked my oil dipstick and cap, but everything looks fine. Also, locally the car doesn’t overheat. And I’ve checked my fans which also come on. How can I check my water pump since there is no visual leak? Or should I just get it changed anyway? Any suggestions are helpful.
Sorry, but I forgot to mention that I also changed the radiator cap.