The often referenced Stant caps are full-pressure caps as far as I can tell, but I would like to try a partial-pressure cap if there is still a good one being produced. I've seen reference to a mopar partial-pressure cap but don't have a part number for it and the local Dodge dealer says their catalog only goes back to 1984.

So, what radiator caps are others using? And does anyone have a part number for a mopar or stant cap that is a double seal (for overflow tank) and partial-pressure?

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'66 Dodge Dart

partial pressure? I dont get what you mean. Stock caps are ~14-16ish lb rated, do you mean something with less pressure? Or a flip cap to vent the pressure before you twist it off?

SlantSixDan has some excellent write ups on allpar about the Mopar style rad cap that has a free hanging valve. This causes no pressure while the engine is cold (off sitting in the garage) and then starts building pressure once the temp comes up enough. The rating of these stock style caps is identical to the full pressure style that use a spring to build pressure even when the car is being stored.

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'66 Dodge Dart

Nothing special sounding about that
Sounds like about any radiator cap I have ever m asked with besides the ones that were shot, and never built pressure

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks for jumping in Dan. Do you have a part number for the partial pressure cap in 13 or 14 lbs rating with double seals for use with an overflow tank? Does Mopar still make these caps under some part number I can use to bypass the dealerships inability to look up parts?

I was looking at the Stant site and can't tell if the often mentioned Stant 10229 cap is a normally open or closed type. Looks they have a line called "vented" that seem to be the normally open style but there were no caps in that line recommended for a 1966 Dart.

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'66 Dodge Dart

Sorry, I no longer have any of my cattledog collection that might've once allow me to look up answers to questions like this. "Vented" is Stant's term for "partial-pressure", though, so pretty good odds. The Chrysler cap 3781 830 is a partial-pressure cap; plenty of those all over eBay. It supersedes to 52079880AA, but none of the many pics I find online of this cap reveals whether it is a partial-pressure ("vented") or full-pressure type of cap. Might be worth looking into.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

It seems the Chrysler part numbers that Dan shared are for 16psi caps and I can't find any for 13psi. Also the Stant part number is 10231 but is also a 16psi cap. So there are a couple options out there if you are brave enough to go with a 16psi cap. Personally, I'm currently using a 13psi cap and don't want to chance it with my super old cooling system. But I plan to do a full refresh next year and will probably try out both caps.

Also both caps are 4 notch style if that matters to anyone. And they are both supposed to be free-hanging/partial-pressure/OE Mopar style, but I haven't yet seen either in person.

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'66 Dodge Dart

If you're worried about pressure vs. your cooling system, use waterless coolant which runs at 0 psi.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.