Hi everyone, I have a 72 Challenger with a 318 that has been running super hot since the weather got warm. I replaced the thermostat, since it seemed nearly dead, and the water seems to be flowing in the radiator so I think the pump is working. The fan works too.

The car hasn't overheated yet officially, but the temperature gauge goes past the H pretty often and can stay there for quite a while unless the car is moving (so that the air is flowing, I guess.)

If anyone has any ideas I would appreciate it; I'm scared she'll overheat if I'm stuck in traffic too long or once the hot weather really kicks in. My heater is disconnected and the fan for it doesn't work, so I can't draw off the excess heat by flipping it on, either.

Thanks so much! --Ann

For starters, change the radiator cap & check all your hoses. Fix the heater too...

Does the hose have pressure on it?If so the cap should be ok.If no pressure could be alot of things,does it seem to "use up" the antifreeze?Is the mix 50-50?To much antifreeze will make it over heat.Even a to lean of cylinder conditon can cause a out of the blue "normal" area increase.Any timing changes?

Hey Mig, thanks for your response! Got a scratched cornea (ouch) that kept me off the computer for a while because the screen was too bright too look at, but all better now.

I did check the new thermostat and it seems to be working - boiling was a great tip, thank you! Adding more water to dilute antifreeze seems to help a little, too, but I think you're right about the blockage in the radiator...I notice the car will sometimes suddenly *stop* running hot for awhile, and that seems to have nothing to do with how hard she's working or how long she's been running; it's totally random. Which makes it seem like there's a partial clog that isn't always blocking the flow.

My shop's going to help me flush it before the weekend, so I hope that solves it. I'm glad you brought this up; I hadn't given it serious thought since all looked fine and rust-free on the surface. Thank you so much for your help!!

Thanks for the suggestion! It seems like it's probably a partial blockage, since the overheating is happening in a very on/off way, so I'm getting her flushed out. But adding more straight water definitely helped; I'd bought both straight antifreeze and 50-50 antifreeze without realizing, and adding water is keeping the overall temp a bit lower. I appreciate your help!

sometimes you cant trust a 39 yr old gauge, so i would plumb in a mechanical gauge to see how high the temp is really going even if its just temporary.

if it's cooling fine down the road but heating up in traffic....still alot of issues ...like air flow at idle...pump circulating properly...if cooling at highway speeds I would eliminate the bottom hose as a cause...I fixed mine with a shroud and 7 blade clutch fan..how old is the rad ?...what's the coolent color ? green ? brown ?

Have you replaced the temp. sending unit recently? If you did and it's one from a local parts places (Auto Zone, Checker, etc.) make sure that they gave you a Chrysler one and not a generic GM one. My Charger did the same thing as yours until I put the proper sending unit in. Works correctly now.
attaboy

get a temp gun, and use it to pinpoint the hoses and radiator in different spots, and verify the real temps. as mentioned, sometimes you can't trust the gauge. might be time for a flush and fill, adding some water wetter never hurts.