0.9 pressure cap... why not higher??
 

I've been taken a look at some japanese interviews and I've seen some FDs with 1.3 bar cap on their aftermarket ASTs. I've searched and it seems you don't recommend going over 0.9 pressure caps because the coolant system is not prepared for these pressures. But, which are the parts in danger exactly? The system gaskets, heater radiator, the hoses themselves?
It's known that the higher the pressure is, the higher the boiling point becomes, so theorically high pressures are better in order to improve cooling, isn't it? I'd like to understand which parts are not supposed to keep higher pressures :)

Mazda actually lowered the pressure caps in a TSB as there were reports of coolant hoses failing and catching fire (coolant is flammable).

you answered your own question..... AFTERMARKET.

I run a zero pressure cap with Evans NPG+ coolant. Yes, ZERO pressure. Oh, and my AST is eliminated.

So, for example, if you're running a full aftermarket hose kit stronger than stock, theorically it would be better (in cooling purposes) a 1.3 bars AST cap, do you mean this?

Zero pressure cap? I am not able to understand how your FD cooling system is working actually... :Wconfused

the main reason a cooling system is pressurized is to raise the boiling point of the coolant, Evans is a waterless coolant with a boiling point of +375F so boiling is not an issue, so unpressurized is fine

Doesn't NPG+ require a 0 pressure cap...

not required it will work on a pressurized system, but its not recomended, as it reduces cooling efficiency

ahum..... were do you get a 0 psi cap? I want one :P

all you have to do is remove the rubber seal on the bottom of the valve on your stock cap. but dont do this unless your running NPG+ otherwise your coolant will boil and youll be buying alot more than a new rad cap

yeah, its for NPG+. I was recently "sold" to it :)
I have to eliminate the AST also right?

"have to" no but if you decide to, it wont hurt anything. be sure the cooling system is properly burped before starting the engine, as the system is not pressurized, and as ive realized the AST elimination mod makes filling the cooling system about as exciting as watching paint dry but twice as long! Ive run without an AST with both 50/50 glycol/water and NPG+ and both work fine without it or with it. personal preference, but i personally see it as one less thing to fail and it cleans up the engine bay a little too

:icon_tup: Thanks! :icon_tup:

That would need to be ALL coolant lines, not just your radiator lines. IMO, I would try to run something which would require LESS pressure.

If your car runs on the hotter side the higher pressure cap will give you a higher boiling point, (less pressure = lower boiling point) it has no bearing on your cooling temperatures, if your car seems to run around the 200 degree F then that's where it will remain. Mazda (as stated in other threads) lowered the pressure to prevent (or lessen) the possibility of the turbo hoses developing leaks spraying coolant on the hot exhaust and causing engine fires. I for one went with The Evans setup and zero pressure for several reasons.

your temp gauge will read an average of the temp of the coolant flowing past it. one advantage of raising the system pressure and raising the boiling temp is to prevent localized boiling in potential hotspots. i dont know how rotaries are with this, but in a piston engine its a good idea because it will prevent the coolant in hotspots from boiling and letting areas around the combustion chamber get too hot and potentially causing detonation.

rotaries are more prone to local hot spors due to the higher combustion temps, but with a properly burped system, and running NPG+ it isnt anything to get too worried about on an unpressurized system

so how about a 1.1 bar?

Just a thought...

A car has coolant seals that are going, but not gone. The coolant only disappears after the system is pressurized, and does so in minut amounts. Would running a system with no pressure eliminate coolant loss to a certain extent? Would it constitute as a band-aid?

no, it might just make it worse

Explanation?

the cause of coolant seals going bad isnt the pressure of the cooling system. its generally heating and cooling again and again that causes the seals to crack and wear down, so running a non pressurized system may help, but it might give you like an extra week or so before they fail, and maintaining a 0psi system isnt cheap (but what is on an FD) the only benifit, in realtiy, is being able to add coolant while the cars hot, and it souns cool to say you run an unpressurized cooling system:icon_tup:

so then if i have an aftermarket ast its be alright to run 1.1?

You can run a 21 psi cap if you think your car is some how different from everyone else's. You've missed the point of why it was lowered to .9 bar any way so do what you want. Most the people that run the higher pressure:
1.) need to because there car runs on the higher side and need the added "head room" to avoid boiling over.
2.) track the car or are running a single turbo, and while the possibility of a fire under the hood exist, they are prepared to deal with it.
I still haven't figured out why using the Evans coolant would be considered a band aid, due to the fact that it's always a possibility the car may run a tad bit higher temperature. My interest in the Evans was the fact there's no water to introduce minerals in the system to help the metals eat themselves up (another cause of o-ring seal failure is the thin web gets eaten up) this is generally related to neglect of the cooling system. The zero pressure part is just a plus as well because there's no stress on the hoses and or water pump seal. I would suggest if your going to run higher pressure carry a fire extinguisher.