OK here goes, I have a 2000 LX Accord, 4 cylinder. It started to heat some a while back. It will idle all day with the AC on and never get close to hot. Normal driving does not get hot either. I have replaced the water pump, when we did the timing belt. I replaced the thermostat and the hoses. New radiator cap and cleaned out the radiator. When driving on the interstate for long trips it will start to heat upe especally on hat days, also when going up a steep incline it heats up pretty fast, has not boiled over but gets 3/4 of the way up. Stop for a min. or two and it comes back to normal. Coolant level is good, I bled the air off at the bleeder but may not have done it enough. Both fans run when AC is on and when the temp get 3/4 of the way up the AC compressor cut off. PLEASE HELP, DO NOT KNOW WHAT ELSE TO DO. Love our old honda it is part of the family.

 

First, do both cooling fans turn on when temp is high and AC is Off? If no, the radiator fan switch may have failed open. Radiator fan switch appears to be (honda shop manual) on upper radiator hose fitting at the engine side. You can short connector to switch to simulate closed switch. Fans should both run as soon as keyswitch is On. A boiling water test can be done to confirm switch is closing or not at 199F to enable cooling fans.

If both fans are running w/ AC off and still overheating, suspect thermostat even though it's new. Was this an OEM (Honda part) thermostat or aftermarket.

If you have an IR temp gun, you could check for cold spots in the radiator (flow blocked due to debris/corrosion). If you find cold spots, you need to replace radiator.

IR temp gun is also good to verify engine is actually overheating. You could have a faulty thermister giving false temp readings.

good luck

 

Radiator fan switch is located on thermostat housing, connected to lower radiator hose.