What is the normal pressure of the stock radiator caps?

1 bar= 14.7 psi
.9 bar = 13 psi

Is it better to get a higher pressure or lower?

 

Yeah, it's somewhere around there stock. Higher pressure will increase the boiling point of the system.

Dale

 

So if you wanted a colder engine, you would go lower pressure?

Any benefits besides being colder?

What about causing more wear on the internals?

 

It changes the boiling point of the coolant - Not the temperature of the motor.

Rob

 

You mean it changes the amount of pressure required to release the pressure?

How can you not change the temp of the engine, by changin the temp of the coolant, or when it boils?

Doesn't make sense to me, please explain.

 

At sea level water boils at 212F. I don't have my steam tables anymore, but if I remember correctly at 15 psig water boils at 250F. All ths means is that you can get your motor a lot hotter before the coolant boils out of the system. It does not mean that the motor will run at 250F.

Rob

 

So a higher pressure cap would be the best to use?

as it allows for more heat before it blows out coolant.

 

but wouldnt u want it to blow the coolant out b4 it gets so hot? ok im confused sorry

 

I wish I knew also, I am trying to learn something here

 

Cooling systems used to be unpressurized. You've seen the old movies with steaming cars trying to go up some steep hill? To avoid the constant hassle of boilover, manufacturers built pressurized systems that let the motor get a little hotter before this happens. I don't believe that there is any advantage to running a higher pressure rated cap than Mazda recommends. On the other hand I dont think you want to be blowing water out if your motor gets to 212 either.

Rob

 

I understand now, thank you sir!

 

Keeping the system pressure up prevents cavitation caused by air pockets in the water jacket. When a bubble forms on the surface of the water jacket it prevents the heat transfer and acts as an insulator causing the engine to retain more heat, rather than transfer it to the coolant.

What has been said about the radiator cap pressure rating is correct for the most part. Cooling systems are engineered to operate at a certain pressure rating. Increasing that pressure could exceed the rating of other parts/seals in the system causing failure. Although I doubt going up to 15lbs would cause this to happen in our engines.

 

As a rule of thumb, keep the caps under 20psi for stock cooling systems.&nbsp Anything over 20psi would cause leaks and possible bursting with stock components - you need to run a "race" cooling system with more robust components to run this high of a cooling system pressure.

BTW, 1 bar = 14.5psi.

Caps up to 1.2psi is fine on the street.



-Ted

 

1.2 psi?? Did you make a typing mistake?

 

Yes he did-1.2 bar @17.5lbs

 

I always thought 1.2 bar was 18 psi, cause that is where my engine blew up @ 18 psi.

 

Hope this helps
1 bar = 14.5038 psi
1.2 bar = 17.40456

 

thanks