Correct PSI Radiator Cap for '70 340?

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DustyEd

DustyEd

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I have been using a 16 lb. psi radiator cap in my '70 Duster 340. However, I just stumbled across some info. from AMD that listed a 14 lb. psi cap for this car.

So, what are you fellows using in your '70 340 engines and which is the factory correct cap we all should be using?
 
A 16 lb. cap is the spec. given in the FSM. Keep in mind that this is for stock engines, with new (not 50 year old) factory components. Engine mods and/or old radiators may make you rethink your needs.
 
DustyEd said:
I have been using a 16 lb. psi radiator cap in my '70 Duster 340. However, I just stumbled across some info. from AMD that listed a 14 lb. psi cap for this car.

So, what are you fellows using in your '70 340 engines and which is the factory correct cap we all should be using?
Click to expand...
2# will raise the boiling point 6°. No biggie. I had a old leaky cap on my Swinger and it would overheat with the a/c on. I put a new 16# cap on and now have a heater core leak. Yep,it can happen that way.
 
Food for thought............More pressure is harder on cooling system components, hoses, rad and heater cores

Depending on where you live, your altitude, you may not need such high pressure

I have a junk Dakota, and not long after resurrecting it, the heater core started to 'steam' Before that I had a 1/2T 5.2 Dodge, and later a 3/4T gas powered Dodge. All three have bad heater cores. To change the core you must REMOVE THE ENTIRE DASH. That is correct, remove the entire dash.

So I ripped out the pressure gasket and just run the caps with the upper gasket in place, which allows them to "slop back and forth" between the rad and the overflow tank. Yup. Sometimes I need to add some.
 
Professor Fate said:
A 16 lb. cap is the spec. given in the FSM. Keep in mind that this is for stock engines, with new (not 50 year old) factory components. Engine mods and/or old radiators may make you rethink your needs.
Click to expand...

This question arose from wanting to put an accurate reproduction 16 lb. cap on my son's '70 Sport Satellite from AMD. They are out-of-stock, but they do have the same large rivet type in 14 lb. So, I was going to take the 16 lb. from my '70 Duster 340 and put it on the Satellite. Then, buy the new 14 lb. (if it's factory correct) and put it on the Duster.
 
got my first radiator recored around 1985. The shop (which did nothing else) told me to use a 7 pound cap. It worked with absolutely no problems so it's what I've used on all our Darts for the last 35 years. Like #67Dart273 says above, less stress on the whole cooling and heating system. The car that shows in the "stock" class has a factory 16 lbs cap in the glove box that has never been under pressure...
 
That 15 LB spec is also for stock, copper brass radiators. If you have a more efficient aluminum radiator, then by all means try something lower like a 13 LB. That's what I run on Vixen and it runs cool as a cucumber. We took it into town Monday in 90 plus degree weather and it barely moved the gauge to 1/8 up. The cooling system just works.
 
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