Rep Power: 0

So I bought a 2001 Honda Civic today and it was fine on the interstate. Once it got into stop and go traffic it started running hot. When the traffic cleared the temp went back down. Also the ac started blowing hot at the same time. But now the ac will blow cold again. Old owners said they replaced thermostat 2 weeks ago and that it has never run hot before. Any suggestions where to begin?

 
Rep Power: 314

My money is that the radiator fans stopped working. That explains why your air condition cut out at the same time. Turn your AC on and make sure the fans are running. If it suddenly stops again, pull over and check to see if the fans are running. If they stop it's probably the relay.

 
Rep Power: 0

Would that also explain the over heating? I am a beginner at this.

 
Rep Power: 314

Stop and go traffic heavily relies on the dual radiator fans to simulate driving (to pull heat away from the radiator fins which cool the coolant) So yes, definitely would have an effect on overheating. However, you might not be able to diagnose this unless it happens again. You can always take a precautionary measure and replace the relay. If it happened once, it will likely happen again. However, if the relay is not at fault your wasting money.

If it's hot enough out the fans will actually come on even if the air condition is off to cool the engine down in stop and go traffic.

 
Rep Power: 0

I will start with replacing that. It seemed to be the cheapest thing. I have another problem with this car. On first crank of the day you have to pump the gas to get it to start. Any ideas there?

 
Rep Power: 519

If the engine is truly overheating, the PCM has the authority to shut down the AC.

 
Rep Power: 194

Do you know how to pull spark plugs?

Let it sit over night, pull the plugs, crank the motor (with the plugs out), go back and check around the spark plug holes for coolant. That could be causing the rough start in the mornings.

Is the coolant full? Check overflow and radiator (with the motor cool).

 
Rep Power: 314

Good to know. I'd still start with the fans lol. Start the car, turn the AC on and check to see if the fans are running.

It could be coolant in the cylinders, however I'd start elsewhere first...

 
Rep Power: 0

I do know how to pull plugs but it seems like it could be a throttle type thing on starting. After you start it once it is fine each other time. Thought I may try cleaning it.

 
Rep Power: 813

turn the a/c on with the hood open and see if both fans come on. if not, then test each fan motor directly to the battery. then check the relays and fuses. might need a new motor. also it could be a bad thermostat. they prolly used aftermarket which is really terrible and can make the engine run hotter than oem. get a honda thermostat and replace that too. altho, usually a stuck closed thermo will cause overheating more when the car is moving. fans seem to be the most likely, since on hot days at idle they are needed to cool the engine. when car is moving, the air blowing in thru the grill is enough.