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hey all my name is jon and i have a 1991 honda civic with a 1.5 and it seems to run cold mostly when the heater is on but sometime when its not on so i changed the thermostat today and that didnt help it seemed at first like the thermostat was sticking open but i dont think thats it now.when i turn the heater on the temp guage drops fast and so does the temp of the air blowing out of the heater.Does anyone have any ideas on what i should check next? thanks in advance.

 
Rep Power: 811

could be alot of things. does the coolant level drop at all? you might have air in the system, or the heater core may be clogged, or bad radiator cap.

 
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yea the coolant level seems to drop and i did just replace the radiator about a month ago is there a way i can bleed the air from the system? thanks for the input

 
Rep Power: 811

warm up the car, turn off the engine, and very carefully with lots of towels around it open the radiator cap. coolant will splash out. turn the car on and let it idle for 15-30 mins. you may need to rev the engine sometimes to keep the temp up. turn the heater on max hot with full fan and watch the air bubbles come out the radiator. keep adding coolant to keep the level near the top. this works best if you park on an uphill incline. if it doesnt work, or air bubbles never stop, or you start losing coolant again later, its most likely a headgasket leak.

 
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when i had it running today to top off the radiator after i replaced the thermostat i could see alot of bubbles coming up as i poured the coolant in and i just filled it to the top and put the cap on so maybe i just need to get all the air out of the system because i didn't know this when i changed the radiator i just filled it up.and thought that was it.

 
Rep Power: 811

ah okay yes, if you just changed the coolant, there will be alot of trapped air. this makes the engine temp sensor not work properly and can even cause overheating along with water rushing sounds under the dash. also until you get most of the air out, the overflow coolant will get sucked into the radiator and not show the actual level. i had the same issue recently after changing the coolant. just spend about 30 mins on a hill / and bleed the air out.

 
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thanks a million i will get the air out of it today and see if that helps.

 
Rep Power: 290

Did you really tell him to take the radiator cap off after warming up the car?

 
Rep Power: 811

yeah, its easier than trying to warm it up with revving from a cold start. just wrap some towel around the cap, it will be okay lol.