Very strange heating issue
 

i have a 2001 honda civic EX. about a week ago my cars temp. began rising. never overheating. i flushed my radiator and added new coolant. problem proceeds, however i noticed that my cars temp only begins to rise while on a downhill. going uphill, the temp. begins to lower. i changed the thermometer, issue persists. any help? any ideas?

also i may add, that i have a buddy that is an aeronautical mechanic, and is capable of doing just about anything so any answers are much appreciated.

Does it overheat at idle? Did you bleed the system after flushing the coolant system?

Based on the hill scenario you describe, my guess is that your water pump is on the way out. You're accelerating while going uphill, allowing the water pump to spin faster and move the coolant. When going downhill, you're coasting a lot more, which means the water pump would slow down the flow, thus increasing your engine temp. If it was a fan not working, I would think the engine temp would be the opposite.

Car has not overrheated, and does not get hot at idle. And bleed the system? Im sorry, im not the most mechanically inclined person... But thanks! Is the water pump a simple task to replace?

Bleeding the system is very easy. Google it and you will see.

Water pump is a much, much, much more involved type of job. you would be replacing the timing belt at the same time.

Thanks guys. I really appreciate all the help. Ill get workin on it this weekend and give an update