Radiator cap lbs

[Jakedog]

I'm currently running a 19-21 lb cap. I have ran this cap without issues for about 3 years now. I'm thinking of running a 15 lb cap to take some pressure off the cooling system.
With my current setup my temp stays around 180-185 while driving and about 195-200 idling in traffic when the weather is 105.

Anyone here running a 15 lb cap or lower in hot weather without heating issues?
My temps are good, I just worry about the extra pressure on the cooling system.

 

[Jakedog]

Sorry. I forgot to flip the photos before I loaded them.

 

[SHX669]

I've been running 13#s on both Broncos for 8-10 years with no issues.

 

[B RON CO]

Hi, on my 66 Bronco and 66 Mustang I run 7# caps.
I would rather blow off pressure ( which doesn't happen) then blow the old radiators or heater cores.

I don't think you will effect the operating temperature of your Bronco by going to a lower pressure cap.

The guideline I learned is that for every pound of pressure you increase the boiling point of water 3*. So a 20# cap, x3 will increase the boiling point of coolant by 60*. 212 + 60 =272*. A 15# cap will make the boiling point 257*. My 7# cap will make the boiling point 233*.

Modern engines run hotter than older engines, where the fan may not turn on until the temp sensor reads 225*. Racing engines run hot because they are built differently, for maximum power.

Unless you run hard on the trails, high RPM with low airflow through the radiator, you shouldn't need a really high radiator pressure cap.

Good luck

 

[Broncobowsher]

Typically run a 13 pound cap. Never boiled one over even in AZ.

 

[gnsteam]

I’m running a 13lb cap on my stock 302. No issues at all.

 

[Jakedog]

Thanks guys.
I will try a 13-15# cap and see how it goes.

 

[blubuckaroo]

Some of the aluminum radiators come with recommendations for a higher pressure cap like yours.
I still can't wrap my head around that.?:?
I wouldn't trust the intake manifold gasket to 20-21 psi.
Mine's a 13 pound cap.