radiator cap

[rob92XLT]

im completely rebuilding the cooling system in my 92 xlt and i have a couple of questions about the radiator cap if any one can help, what kind and how many pounds should it be....i am going to get a all aluminum radiator if that makes a difference.....

 

[Maniak]

The highest you will find in town is normally 16psi.

According to Stant, a stock cooling system can handle 19-21psi caps with no problem but you have to order those.

As you increase the PSI of the caps you are increasing the boiling point of the water. You gain 3F for every PSI. So a 16psi cap increases the boiling point of water from 212 to 260.

I have found 16psi keeps the water from boiling even after I park the truck after driving in 110F weather.


~Mark

 

[410Fortune]

So should I ditch my 7# cap?

I think I had it backwards, I though less # = better.

You see you learn something everyday.

Of course my truck runs at 190 and hits 220 in extreme situations but cools right back down........

 

[Maniak]

It doesn't really affect the temp of the water, it affects whether or not the water boils.

With a 7psi cap (assuming no antifreeze) the water in your radiator will boil @ 233F, and once the pressure reaches 7psi it will let the water out of the radiator.

Both are bad, you don't want the water to boil, and you don't want the water to leave the cooling system.

~Mark

 

[Runnin'OnEmpty]

According to my anti-freeze jug, a 50/50 mix gives a boiling point of 265*F when using a 15# pressure cap.

So by my calcuation, a 7# with 50/50 mix gives protection up to 241*F.

I run a 7# cap (with 180* thermostat) on my Cherokee with no problems so far.....

 

[Maniak]

Yes, Antifreeze does increase the boiling point.. BUT it hurts the heat transfer properties..

I was giving raw numbers (water only), not numbers with antifreeze... The only reason I run antifreeze for the anti corosion and lube properties... I only run 25%

~Mark