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What is the purpose?


dvdswan

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I picked up a new radiator cap and noticed... The new one is a RS-90 and the old one is a RS-77. The difference is the RS-90 is 16 psi and the RS-77 is 13 psi.

So what is the purpose of having different PSI ratings on the cap? I do know that the higher the PSI the hotter the temp takes the water to boil. But wouldn't that do more harm to the engine?

The biggest question is, which one is the correct rad cap for a 91 3.0l v6? Everything I find says "fits your vehicle".
 


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dirtymike

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I don't know which cap to use but what is the temp on your t-stat. Would this increase or decrease the level of antifreeze you have in the overflow?
 

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The radiator cap determines how much the coolant system will be allowed to pressurize to, before it opens and allows coolant to flow to the overflow tank. I'm not sure what the 3.0 calls for.
 

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3 psi will change the boiling point 9 degrees... not a huge difference... so I doubt it would hurt the engine. But It could make a difference in some climates... driving across the desert comes to mind. It will also put more stress on the entire cooling system. Might not be a great move on an older cooling system.

I'm not sure what factory used... maybe in the owners manual. If you weren't having problems I would get the same one you took off.
 

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I do know that the higher the PSI the hotter the temp takes the water to boil. But wouldn't that do more harm to the engine?
No, if the coolant boils in the engine you now have vapor instead of liquid in the system and vapor WILL NOT cool the engine. So if you overheat slightly because of say a fan failure, with say a 10psi cap you will have a cascade effect since the coolant can boil at a lower temp and stop cooling the engine causing the engine to overheat more and more. Same scenario with a 16psi cap and the coolant will remain liquid and keep cooling the engine and potentially preventing a catastrophic failure. At normal operating temp it doesn't matter since both pressures are enough to keep the coolant in liquid form, using the higher pressure cap doesn't mean you raised the pressure of the system, only the point at which the cap releases.
 

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SSSSssssooooo......?


Did the OP get his question answered? Because, .... I.... we, yeah, WE got lost in all the math stuff.
 

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SSSSssssooooo......?


Did the OP get his question answered? Because, .... I.... we, yeah, WE got lost in all the math stuff.
I was simply answering one of his questions. :icon_rofl:

I have no clue what the OEM pressure is. My 2009 is 16psi but it's a degas system so completely different style cooling system. :dunno:
 

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I was simply answering one of his questions. :icon_rofl:

I have no clue what the OEM pressure is. My 2009 is 16psi but it's a degas system so completely different style cooling system. :dunno:
Which one did you answer? :icon_confused:
EDIT: Nevermind found it. = Question; But wouldn't that do more harm to the engine? Answer; At normal operating temp it doesn't matter since both pressures are enough to keep the coolant in liquid form, using the higher pressure cap doesn't mean you raised the pressure of the system, only the point at which the cap releases.
 

dvdswan

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Thank you for the replies. I do appreciate the education of it. I'll keep looking for the proper cap pressure as I still have the original owner's manual. Honestly didn't think something that specific would be put in there, but if they list the filters required for maintenance then they should list the rad cap.

Again, thank you.
 

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dvdswan

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Maybe I should look in the Degaba system. lol

So if your system is the degas, is there a name for the 2nd gen cooling system? Just curiosity.
 

Dirtman

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Maybe I should look in the Degaba system. lol

So if your system is the degas, is there a name for the 2nd gen cooling system? Just curiosity.
Uhhh "normal" cooling system maybe, i don't think they needed fancy name for it? :dunno:

Only over complicated new things require fancy names. :icon_rofl:
 

dvdswan

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Gosh, I feel left out with no special name... :cry: do 2nd gens get to have a trophy for showing up at least... :tease:
 

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That system is just standard I imagine, it's what pretty much everything used in the way back machine up until they came up with the degas setup, not sure what was the first thing to use it but I know the 7.3L powerstroke's used it back in '94...

Blindfold yourself, put both caps in a bowl and swish it around then pick one out and use that one... You're in Seattle, it doesn't matter, keep the coolant full and the transmission cool and you'll probably be fine with either... :). If it were me I'd probably just put the 13psi cap on and throw the other in the glove box...
 


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