barrybong34

I have a 99 civic dx. I have replaced radiator, thermostat, fan motor ,all the temp switches, water pump, timing belt, head gasket, and have flushed the system repeatedly. I can start the engine and let it idle runs perfect for as long as you want to let it run. As soon as i drive it the temp goes to hot. I turn the heater on and it cools right down and stays cool while driving or sitting. Shut car off for 15 - 20 mins get back in to drive same thing heats up until i turn heater on. Radiator fan does come on and cycle on and off but only after i run the heater and bring the temp back down. Any ideas or suggestions on what i should look for or do next?

00civic-ej8

Just curious have u bleed the coolant system that might be it my other honda i had did the the same and all it was was just to bleed the system and BLAM stoped overheating soo just an idea u could try

barrybong34

Yes i have bled the system everytime i make a change.

00civic-ej8

Ok run another idea go out to ur car and have it running for a while before the car gets hot and with a thermometer the laser one look at the heater hoses and look at the temperature for both of them if one of the hoses is significantly hotter than the other one than u might have a clogged heater core and u could get away by bypassing the heater core if that is the problem since a clogged heater core can also make a car over heat and almost do the same symptoms

barrybong34

Even though it cools down the engine everytime i turn the heater on and stays at normal temp once temp gets down. You think it is possible the heater core is plugged?

00civic-ej8

I think it might be like i said get one of those laser thermometers or some other thermometer that can read temperature and see if one heater hose is significantly more hotter than the other its normal if they are of by a couple degrees but if its allot then well theres ur answer, u can bypass it by just connecting a hose to upper and lower heater outlets in the back so coolant will constantly flow trough and not clogg up

barrybong34

There is about a 50 degree difference in the heater hoses after the car ran for about 15 mins

00civic-ej8

Yes thats a big diffrence ur heater core is probably clogged now to bypass ur heater core u can just use a piece of hose and hook the upper and lower heater core outlet things on the engine together allowing for there to be free flow going trough there and then just when u have a good two whole days of free time take apart ur dash and slap that heater core in

barrybong34

Bypassed the heater core and bled the system. Let car idle for about 30 mins with a/c on for most of that time. Topped of radiator amd drove car about 4 miles with a/c on. Its 111° where i lve and the temp gauge barely went over half way. Thanks for your help. Greatly appreciated!!!!

00civic-ej8

You are very welcome man i had a 99 grand prix gtp that did the same thing a fellow tech of mine told me to do that and it worked so now when u have time get ready to take apart that dash and put in the heater core and also maybe the evaporator core for the ac i think its there not sure but while ur at it replace the heating and cooling system parts that are under the dash so u can get that headache out of the way in the future