Really 20# Radiator cap pressure

[Cobraman]

Just thought I would verify that FFR sends out their kits with 20# radiator caps. This seems a bit high for my liking every truck,car I've ever had with a 351/400 has a 13 to 15 psi cap.
I know that my 408 is diffently not stock and needs plenty of cooling. I'm running a 190° thermostat and it really doesn't get above 190 at any time idle or driving hard . I admit I have no body on it yet but still think it's putting undo pressure on the system unnecessarily.
Just looking for some input as to what everyone else is using.



224725224726

[PMD24]

My MK4 roadster kit came with a 26psi cap. Seems high, so anxious to see the feedback here. I recently saw an ie 427 video where I think Frank indicated he switches to a 10psi cap.

[gbranham]

I use a 10# cap on my 427.

Greg

[StangRacer]

The only purpose of using a higher PSI cap is to raise the boiling point of the coolant. I don't recall the exact figure but for every PSI it raises the boiling point 3 or 4 degrees. It will not make a difference in the temperature of the coolant. As long as the cooling system consists of components suitable for higher pressure there is nothing wrong with running a higher PSI cap. I have no idea at what pressure the supplied FFR components are rated at... when I road raced, I used a Moroso 23-25 cap but had braided hoses with AN fittings. I don't think I would run a cap with that high a PSI relief with rubber hoses and normal clamps.

[CraigS]

Heck don't FFR radiators leak enough already? Why put a 20# cap on the system?

[weendoggy]

I'm going to ask if the radiator itself has a cap, or, is it sealed off permanently with NO cap. If you have a cap on the radiator, you would want that to be higher than system (usually 16#) if you plan on using a "easier-to-get-to" cap/filler.

My radiator is soldered shut completely with no cap. I use a 16# in the position you have in your photo. I have no issues. I believe F5 had you put a higher rated cap on the radiator, due to it's "not easy to get to" feature and place one as you have, only a lower rated cap. This prevents the radiator from blowing the cap and instead blowing the lower pressure one.

[gbranham]

My kit-supplied radiator (July 2023) has no cap; just petcock for draining it.

Greg

[Cobraman]

Looking like I may try a different cap something in the 10 to 12# range it's always good to bounce these issues around with the fourm.
Thanks

[Cobraman]

I'm going to ask if the radiator itself has a cap, or, is it sealed off permanently with NO cap. If you have a cap on the radiator, you would want that to be higher than system (usually 16#) if you plan on using a "easier-to-get-to" cap/filler.

My radiator is soldered shut completely with no cap. I use a 16# in the position you have in your photo. I have no issues. I believe F5 had you put a higher rated cap on the radiator, due to it's "not easy to get to" feature and place one as you have, only a lower rated cap. This prevents the radiator from blowing the cap and instead blowing the lower pressure one.


No cap on radiator just as my pic's show

[weendoggy]

No cap on radiator just as my pic's show

Couldn't tell by your picture, but if that's all you have, it's too much.

[i.e.427]

I recently saw an ie 427 video where I think Frank indicated he switches to a 10psi cap.

We recommend a 10-12 lbs cap just like the ones that originally came with the SBF engines back in the 60's when they were introduced. A properly working cooling system with a SBF does not require anything higher.

11 min. mark of this video is where we talked about it.

https://www.youtube.com/watch?v=1CVTZ9tXNSw&list=PLDlFwXKm54ocTfAY0kLnGZAtlIL_i4FJ6&index=40

[Cobraman]

We recommend a 10-12 lbs cap just like the ones that originally came with the SBF engines back in the 60's when they were introduced. A properly working cooling system with a SBF does not require anything higher.

11 min. mark of this video is where we talked about it.

https://www.youtube.com/watch?v=1CVTZ9tXNSw&list=PLDlFwXKm54ocTfAY0kLnGZAtlIL_i4FJ6&index=40
Thanks Frank ,that's exactly what I thought just verified

[cv2065]

If the boiling point of say Prestone 50/50 coolant is 265 degrees F, is there a reason why a radiator cap needs to be pressurized? I'm assuming that the system needs some kind of pressurization from the cap beyond just increasing the boiling point.

[rich grsc]

That is with a 15# pressure cap, open atmosphere is around 226*

[StangRacer]

If the boiling point of say Prestone 50/50 coolant is 265 degrees F, is there a reason why a radiator cap needs to be pressurized? I'm assuming that the system needs some kind of pressurization from the cap beyond just increasing the boiling point.

The coolant isn't at a constant temperature across the entire cooling system. For example, there may be hot spots above the combustion chambers or around the exhaust ports in the cylinder heads. Increasing the pressure of the entire cooling system will prevent boiling at that those spots.

[Valkster]

Thanks for this post. I was in the process of changing the hose routing in my build and noticed that the cap was 20psi. I think the engine in mine originally had a 13psi cap (old 428FE). Can anyone tell me what the source of the inline cap body and cap are from? What I mean is that my housing has no part number on it and I wanted to know, in case I ever had to replace it, what make/model car it was for or what part number the housing is. Thanks for any insight.

-Mark