James has the first best answer. Radiator is plugged, unless you are losing coolant rapidly (head gasket failure). At 65 mph the fan is not needed. Not the thermostat for the reason Joser gives.
You have tap water in it, right? Tap water is poison to radiators, causing the tubes to become blocked with hard water deposits... limestone. No flush will touch that stuff. I even tried straight CLR once with no effect. If the radiator is plugged you need a new one, and proper antifreeze (not conventional green, either). How to know? Pull the hoses off the radiator and stick a garden hose in the top fiting. A good radiator will easily pass all the water a garden hose can put out. If it comes back out the top, the radiator is history.
sounds like maybe the electric fan is not coming on when it should.
Put coolant In It not water. Water boils way faster than coolant.
plugged radiator... maybe?
sounds like maybe the electric fan is not coming on when it should. this could be from a relay or sensor not working. check it or have it checked. running an engine hot is a big no-no and one of the fastest ways to do harm to it.
So, I bought this car a week ago. It was sitting in a garage for about a year. It has 135k on a rebuilt motor. It has the d15b1 motor. It's a 1989 civic ef hatchback. Question being; whenever I'm on the highway or going up a hill, even I my car doesn't have allt of weight and I go to pass, the motor goes hot. Would this sound like a thermostat? I'm running water in it right now.
