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340 running hot

JG1966

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My 340 72 RR is running hot after about 10 minutes on the road. Right around 210-220 (Stock gauge goes to a little before first "hot" line). It stays cool when it's idling forever but as soon as I get on the road, it starts to creep up. Timing is right and not running lean. Switched from 160 to 180 thermostat. That helped a little. I suspected 26 inch radiator might be clogged (it doesn't seem to flow very well when I ran with cap off). But wouldn't it get hot at idle if radiator was clogged? I have 18 inch flex fan with shroud, non ac water pump and pulleys. I do have a 3000 stall and wonder if that may be causing my heat (using both radiator and separate tranny cooler). From reading on this site (lots of overheating issues with Ma), I know it could be a dozen or more things causing to run hot (and spit coolant). But does fact it stays cool at idle eliminate or point to something? Thanks
 
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OK at idle, hot at speed, sounds like air trapped in the cooling system.
 
Just a thought. Do you have a spring in the lower rad hose? The lower hose should have a spring inside of it. This is because the bottom hose is the suction side where the water pump sucks water out of the radiator and pushes it through the engine. When the spring is removed or it simply rusts and disintegrates, this leaves nothing to prevent the hose from collapsing under the suction of the pump. If the hose sucks closed, it cuts-off the water supply to the engine.
 
Just a thought. Do you have a spring in the lower rad hose? The lower hose should have a spring inside of it. This is because the bottom hose is the suction side where the water pump sucks water out of the radiator and pushes it through the engine. When the spring is removed or it simply rusts and disintegrates, this leaves nothing to prevent the hose from collapsing under the suction of the pump. If the hose sucks closed, it cuts-off the water supply to the engine.

Thanks Moes, but I definitely have a spring in the bottom hose. The bottom hose is cooler than the upper hose, too, which leads me to believe the radiator is working. It just doesn't seem like it's flowing as much as it should. I can see it moving but it's very slow.
 
Another thought. Is you fan half in and half out of the fan shroud, if it is in to deep in the shroud you would create an air dam between the rad and the fan and you do not get a good flow of air from the rad
 
The lower hose could collapse if the spring inside it is bad at higher rpm. Faulty Radiator Cap, bad water pump.
 
Another thought. Is you fan half in and half out of the fan shroud, if it is in to deep in the shroud you would create an air dam between the rad and the fan and you do not get a good flow of air from the rad
Yes. I checked that. Fan placement is halfway in, halfway out of shroud.
 
The lower hose could collapse if the spring inside it is bad at higher rpm. Faulty Radiator Cap, bad water pump.
Thanks Coronet. I will check to make sure spring in bottom hose is good. The radiator cap is a 16 pound from Summit that seals fine. Water pump appears to be good and is definitely moving coolant into the radiator at top and out of the radiator at bottom.
 
When did this start to happen? Did you make any changes to the car?
 
When did this start to happen? Did you make any changes to the car?
No changes. I bought the car in October. It's my car from high school in late 1980s that I sold six years ago cuz I was broke. It had sat in my garage for 15 years undriven as life happened and I didn't have time, money to fix her up right. But I kept in touch with the guy who bought it. He painted it, new rear end, new tranny, lots of upgrades, etc., and I was lucky enough to be able to buy it back from him after I turned my life around and saved some money. She's my baby. It always ran a little hot when I drove her in the early 1990s but not this hot. It's the exact same motor I put in her in 1987. He put about 1,000 miles on engine in the five years he owned it (in another car). Changes to drivetrain since I sold her six years ago is gears (3.91) and stall (3000).
 
Me and Christine in 1987 and again in 2016 after I bought her back.
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14939368_1202236699869712_5590194958547905265_o.jpg
 
did you check to see if the flow in the rad increases as the rpms went up or did the flow stay the same? If it stays the same, your rad is clogged. Bring the rpms up to 2500 or so and check the flow, it shoud flow faster. Did you check temp sender in the block with a heat gun, to varify the temp was correct on the gauge?
 
did you check to see if the flow in the rad increases as the rpms went up or did the flow stay the same? If it stays the same, your rad is clogged. Bring the rpms up to 2500 or so and check the flow, it shoud flow faster. Did you check temp sender in the block with a heat gun, to varify the temp was correct on the gauge?

The temp sender is good (10ish ohms at cold, up to 70 or so) and I'm fairly sure the gauge is accurate (the spitting coolant was enough for me to know it was hot like the gauge said). I will definitely check the flow with raised RPMs. Thank you. I've only put 5 miles on engine running hot and I'm not driving again til I get it right.
 
I really believe from what you've stated that your radiator needs to be rodded out. It has some flow but if the tubes are calcified inside there is not enought heat transfer. If this car sat around for several years you should get the radiator cooked out. Cheap insurance and not that expensive. If your running a high stall converter you may want to consider getting a 3 or 4 core rad core put in your original radiator because there is going to be much more heat generated on the highway at rpm. Especially if you have the basic 2 row rad core now. Just a few things to think about to help out. Nice looking Plymouth.
 
My 340 in my 73 runs warm, but not hot, I am using a 195 thermostat but have my radiator upgraded to a 4 core when it was rebuilt, and even in hot weather the temp gauge never goes over the midway point. I think MW413 is correct that you should check your radiator and have it boiled and rodded. Why such a high stall, I would think you should be closer to 2500 or between 2300 and 2500 depending on what cam you are running.
 
My 340 in my 73 runs warm, but not hot, I am using a 195 thermostat but have my radiator upgraded to a 4 core when it was rebuilt, and even in hot weather the temp gauge never goes over the midway point. I think MW413 is correct that you should check your radiator and have it boiled and rodded. Why such a high stall, I would think you should be closer to 2500 or between 2300 and 2500 depending on what cam you are running.
Thanks. You guys confirmed what I suspected all along. I'm getting new radiator (it's 45 years old). I have a .292 duration, .509 lift cam. I may need to go to smaller converter (and maybe a smaller cam) some day but I like the combo for now.
 
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