I recently acquired an 05 Accord, and am trying to troubleshoot an overheating issue. After driving the car for about 30 minutes, the heat starts to creep up - within five minutes the heat will reach redline. During the 30 minutes prior, the temps have been fine, even in 100F Texas heat, driving highway speeds, with the AC cranked up. After trying to reproduce it a few times, I found that if I see the temp starting to rise and turn off the AC, the temperature will stabilize as long as we're moving. After about five minutes with the AC off, if I turn it back on the temp will drop back down to normal again.

I've stopped the car and checked under the hood as the temperature is climbing, and both fans on the radiator are running still. I'd expect the temperature to not recover if it was the water pump. Since re-engaging the AC seems to resolve it (and turning off the AC stops the immediate climb) I'm looking at that system primarily - is there another fan or pump triggered by the AC compressor? My only other thought is debris in the radiator - if some small bits of stuff are getting caught in a corner, re-engaging the AC might up the flow and knock stuff loose. Any thoughts?

 

welcome to the forum if both fans are running with the a/c on which is correct, what may cause the temp rise could be the radiator top has corrosion from the years of antifreeze, especially if not changed once a year, also the thermostate is beginning to stick closed, also check to see that the radiator front is clean, sometimes dirt or trash can accumulate between the condenser and the radiator, and last item would be the water pump starting to fail unless changed at timing belt change.

 

Thanks for the reply! The thermostat is easy to replace... It would be great if that was my cause. For the radiator - how can I diagnose that? If I do a coolant flush will I see evidence?

 

you can do a reverse flush. disconnect lower hose and hook up a water hose and an air gun, disconnect the top radiator and put a nylon hose or anything to catch scale/debri. as you fill the radiator with water from the bottom, blow the air gun compressed air into the system. this should blow water and air and the debri if any will collect in the nylon hose or cloth bag to see what comes out. if there is nothing, then the problem is else where. note sometimes the corrosion on the top of the radiator will not fall off and stay adheared to the top of the fins. safe way is send the rad out for rod out or replace the core.