Hey all.
New on here but avid reader. I just got a 97 civic and I'm having a overheating issue. Changed out the t-stat and flushed coolant. The weird thing is it runs normal till I get onto the highway at about 60 mph is when it overheats.... Also idle jumps from 1k -2k after warmed up. No engine lights, so no codes.... Any ideas???
Thank D.

 

Was the coolant system properly bled? You would need to turn the heater on full and park it on an up hill incline, pop the hood, take off the radiator cap (when cool!), and start it up. Let it idle until it reaches operating temperature. The radiator fan should kick on. Add coolant as needed to the radiator itself (not the plastic overflow container).

This will tell us two things: 1, that there is no air in the system, and 2, that the radiator fan is working.

 

Driving and overheating sounds like a water pump issue as the coolant is not circulating while the rpms are up as it should. Make sure all air is properly bled prior to assuming this.

I am not sure on the idle issue though.

 

I bled system till air bubbles stopped coming to top and could see a good flow, fan kicked on at normal temp. I'll order the water pump and timing belt and try that out. The idle issue had a friend look at it, he unplugged one of the fuel injectors and the idle went to normal plugged it back in and idle jumped???? Air/Fuel must be wrong this is mind blowing..........

 

Water pumps rarely fail to pump unless the impeller has been corroded away by using plain water or very old antifreeze. More likely the radiator is clogged, especially if a "stop leak" compound has ever been used in it.

Make sure you aren't losing coolant from the radiator, it should be full to the top every time you check it (cold). Drive for a while but don't let it overheat then cool off and check it. Low coolant will cause inconsistent idling, or it could be a completely unrelated problem.