I have an aftermarket PFS AST. It has a pressurized cap (13LBS)

I also have a blitz pressurized water cap on the water neck. (1.3 KG/CM)

Should both caps be pressurized? Does it matter?

 

no, use the pressurized one only on the AST and a no pressure cap on the water filler neck

 

Yeah, only use one pressurized cap, using two increases the amount of pressure in the system, it will have to create more room for expansion.

 

no pressure cap on the Waterfiller neck? O.o hmmm.. mine has a pressure cap. stock. Rx7store sells the pressure caps to replace OEM...

 

the only time you run a pressure cap on the filler neck is when you delete the AST...

 

Werd.

 

Could this cause antifreeze to get pushed out of the fill up the tank vent?

 

You mean no pressure on the overflow tank?
Don't you have to use pressure cap on the filler neck?
The stock filler neck cap is pressurized and so is the stock AST cap.
Am I missing something? Doh! I guess I better check mine...

 

I have a pressurized cap on the filler neck, and a pressurized cap on my aftermarket AST.

Quite simply, are they both necessary?

 

I thought you have to have pressurize cap on both except when you run NPG?
I'm hoping those guys would chime in...

 

Nope. For the usual AST setup, any cap that plugs up the filler neck should be sufficient... like the simple flat stock cap. Though, a pressure rated cap should still seal the top of the filler neck just the same. But, to be clear, you do need a pressure-rated cap (the ones with the springs) for the AST.

 

It seems like a few people here don't quite understand how radiator caps work. A cap with a spring in it is a pressure RELIEF cap. A 13lb cap will release pressure if it gets above 13psi. Using two pressure caps makes no sense, it's redundant and there is no need for it.

You might have problems somehow, if they both relieved too much pressure at once, pressure might suddenly drop from 14 >>9 psi, reducing the boiling point quickly and allowing the coolant to vaporize. I'm not saying that this will definitely happen, but it's a worst case scenario that I can think of.

http://auto.howstuffworks.com/cooling-system7.htm

-s-

 

Just to eliminate confusion:

In the stock setup, the filler cap SEALS TO THE ATMOSPHERE, but lets coolant flow freely (at internal coolant pressure) to and from the AST. The AST cap is a pressure relief (0.9 BAR) and coolant return cap. This vents to the overflow tank when internal pressure exceeds 0.9 BAR, and draws coolant back to the engine when the pressure in the engine drops below atmospheric (vacuum) as it cools and the coolant contracts.

 

just to add confusion ...

With stock set-up (ast), any pressure regulating cap can be used on the filler neck, since only the ast cap rating will control system pressure.

But, the stock filler cap (no internal spring) is designed to seal 15+ psi at the rim of the neck. Typical regulating caps (with internal spring) don't normally see pressure at that location, only slight vacuum. The pressure is controlled by the lower rubber washer, below the spring.

So ... although a typical regulating cap (with spring) will work at the filller neck, it is the stock cap (no spring) that is designed for that location, and is less likely to leak.

 

I have been running with both pressurized caps for close to 2 years. I am guessing, based on the time, that it is not going to kill anything.

 

http://www.scuderiaciriani.com/rx7/cooling.html#CAP