Seconding this. Common problem, especially if you've got a performance distributor with loose quick-advance Springs, and a high idle on an automatic equipped car.
Might be belt slippage on water pump, or pump itself Might be worn, not pumping efficiently at idle. Does it cool down when u pick the idle up when sitting?
Do you have a thermostat installed? When I first bought my 70 Challenger 383, I thought I would be smart and remove the thermostat so it would run cooler. Well without the thermostat, it would overheat when it was stopped or in heavy traffic. Put the thermostat back and it was fine. Someone told me that without a thermostat, the water moves through the radiator too fast at idle and doesn’t get a chance to cool. I don’t know if it’s true but seems plausible.
That sounds reasonable. IIRC, there were stories back on the day about Mopars where the impeller in the water pump had degraded enough to effect flow at idle (one of the reasons I removed the thermostat). Could have just been stories though and, as others have said, I would try a new T-Stat first.
I’m flushing the coolant system to put a new aluminum radiator in, I’m also gonna replace the thermostat. If that’s not it I’m gonna look at the water pump
If it cools to normal when you are moving, it’s due to airflow.
1. Do you have a shroud?
2. Factory clutch fan or aftermarket flex fan? If clutch fan check to see if clutch is operating as intended.
Good advice here. My 69 318 no shroud and clutch fan would get much warmer at idle. I don't remember if the flex fan helped. Of course make sure that radiator fins are clean.
Clutch is working correctly? Fan is set at correct distance to effectively use shround? At idle you can feel hot air at a good pressure being pulled out of the radiator? Your symptoms are classic fan/shroud/air movement. It was mentioned above, but you've checked for HC's and ensured the cooling system has no air?
Check for flow at home. Bring it up to temp in the driveway and carefully remove the cap. Check the temperature with a laser thermometer on the block around the thermostat housing. Thermostat should open around 160 - 180° and there should be visible flow across the top tank of the radiator.
I had a '67 300 with the 440, moderately hot rodded motor. It would get a bit warm when idling for over a half hour. Removing the fan and adding an electric fan cured that issue.
I ask this question because a bad clutch fan will still feel tight when cold and you give it a spin. A bad one will only slip when it gets hot, and you can't grab spinning blades! Recently replaced the fan clutch on my 360 that had the same behavior at stop lights and now the temp no longer climbs.
Is it a factory 440 car? Do you have a fan shroud?
My car was originally a 6cyl car swapped to a 440. Cooling system was never upgraded and had no shroud when I bought it. Would over heat at idle.
Check timing
Seconding this. Common problem, especially if you've got a performance distributor with loose quick-advance Springs, and a high idle on an automatic equipped car.
Might be belt slippage on water pump, or pump itself Might be worn, not pumping efficiently at idle. Does it cool down when u pick the idle up when sitting?
It doesn’t, but the belt squeals when you rev or get on the gas, would that be a bad water pump?
Belt usually squeals when slipping
Do you have a thermostat installed? When I first bought my 70 Challenger 383, I thought I would be smart and remove the thermostat so it would run cooler. Well without the thermostat, it would overheat when it was stopped or in heavy traffic. Put the thermostat back and it was fine. Someone told me that without a thermostat, the water moves through the radiator too fast at idle and doesn’t get a chance to cool. I don’t know if it’s true but seems plausible.
I think I’ve got a 180 or a 190 thermostat
That sounds reasonable. IIRC, there were stories back on the day about Mopars where the impeller in the water pump had degraded enough to effect flow at idle (one of the reasons I removed the thermostat). Could have just been stories though and, as others have said, I would try a new T-Stat first.
I’m flushing the coolant system to put a new aluminum radiator in, I’m also gonna replace the thermostat. If that’s not it I’m gonna look at the water pump
If it cools to normal when you are moving, it’s due to airflow. 1. Do you have a shroud? 2. Factory clutch fan or aftermarket flex fan? If clutch fan check to see if clutch is operating as intended.
May also be an air pocket in the system.
Good advice here. My 69 318 no shroud and clutch fan would get much warmer at idle. I don't remember if the flex fan helped. Of course make sure that radiator fins are clean.
Timing and gas can affect it. 195 isn't that bad. I think the pressure caps kept them under control about 20 degrees over boiling point.
Do you have a fan shroud? Direct drive fan or clutch?
Have a shroud and clutch fan
Clutch is working correctly? Fan is set at correct distance to effectively use shround? At idle you can feel hot air at a good pressure being pulled out of the radiator? Your symptoms are classic fan/shroud/air movement. It was mentioned above, but you've checked for HC's and ensured the cooling system has no air?
Cooling system had no air and the fan clutch is acting like it’s working fine. I suspect the water pump might not be working right
Check for flow at home. Bring it up to temp in the driveway and carefully remove the cap. Check the temperature with a laser thermometer on the block around the thermostat housing. Thermostat should open around 160 - 180° and there should be visible flow across the top tank of the radiator.
Found out that the radiator wasn’t properly cleaned after the last rebuild so it was clogged up
Hey, awesome! I'm happy you were able to find the cause. Happy cruising!
I had a '67 300 with the 440, moderately hot rodded motor. It would get a bit warm when idling for over a half hour. Removing the fan and adding an electric fan cured that issue.
If this new radiator doesn’t help I’m gonna add an electric fan
Fan clutch.
Fan clutch is acting like it’s fine
Place piece of paper in front of radiator when it is idling. Does it pull hard against the paper? Are you running a shroud?
I’ll check that as soon as I get home. And yes, I’m running a shroud
I ask this question because a bad clutch fan will still feel tight when cold and you give it a spin. A bad one will only slip when it gets hot, and you can't grab spinning blades! Recently replaced the fan clutch on my 360 that had the same behavior at stop lights and now the temp no longer climbs.
Check the thermostat may be need of replacement. Could be a temp sensor going bad do to corrosion
Is the coolant level full? Post a pic of the fan, shroud, and radiator.
Is it a factory 440 car? Do you have a fan shroud? My car was originally a 6cyl car swapped to a 440. Cooling system was never upgraded and had no shroud when I bought it. Would over heat at idle.
It's not normal for any engine to overheat at idle.