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at idle temp rises and heater blows cold air

F

falco321

NAXJA Forum User
Location
NM
I have searched for days regarding overheating and have not found anything that matches my prob. Any help is appreciated.

92 4.0L Outside temp is around 30 degrees.

Temp reading is good while moving. If idling for more than a few minutes the temp goes up well above normal, but has not gone to red. As temp goes up heater begins to blow cold air. If I rev the motor slightly the temperature will fall back to normal. As the temp goes back down the heater will begin to blow hot air again.

Thanks in advance.
 
That was my first thought.

The reservoir was at the add line cold. The coolant was at the neck of the radiator.
 
The cold air from the heater still sounds like coolant level is low. That aside, rising temp while not moving but cools while moving could be the fan clutch. Unfortunately, there is no reliable way to test the fan clutch. If you have more than about 80k miles, it is worth replacing the fan clutch.
 
My second thought would be as stated above. Water pump issue or possibly T-stat not opening enough. There is obviously a coolant flow issue. Check those 2 things and check back.
 
Try the heater matrix i have the same problem changed the matrix and all was ok, The matrix get cloged up and restrict the flow of water around it until you rev the motor hence pushing more pressure around the coolent system
 
Check the vacuum operated control valve in the inlet heater hose. It could be intermittently sticking closed, or the vacuum line going to it could be leaking as well. Cold temps can make the rubber diaphragm inside stiffer. Operate the temp controls on and off and check the valve for movement.


Also possible: Both the heater core and radiator could be plugged with crud.
The water pump could be worn out or the fan clutch might not be locking up.
 
water pump or there is an air bubble in the system. take the cap off the radiator WHEN COLD and start it up. the system will purge itself after 20-30 minutes. just keep adding fluid as it goes down
 
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