.

I know the stock rad cap is 13lbs but, what will happen if i use a 16lbs cap on a stock S4?
could it cause problems?

 

I am pretty sure it's safe to go up to sixteen psi. Just go to Autozone and get a CST brand with the pressure release lever on it. It's like $5 bucks.

 

You should only use a Mazda pressure cap. I can't remember why, but do a search, its been mentioned alot.

 

nah, you can use any cap that's 13-15psi(can't remember if you can use 16psi too)...

i think you meant the mazda Tstat?

 

T-stat for sure, but I thought I heard that Mazda pressure caps were special too.

 

For the umpteenth time, all a high-pressure cap does is increase the coolant's boiling point. At 13psi the boiling point is already way higher than you should ever let the engine get, so more pressure does nothing but increase the likelyhood of a 15+yo hose popping. Higher pressure does not increase the cooling system's capacity and will not help an overheating problem if you have one.

 

Not questioning you, but I'd like you to explain something to me. If what you say is right, and it is, why in the hell do they make higher pressure caps in the first place? whats the point if a cooling system in any car's boiling point is the same psi?

 

I have no idea why higher-pressure caps are available. I have yet to hear even one half-sensible explanation for running higher pressure. Personally I think they're just an excuse to buy another overpriced brandname part.

 

Hey guys, just last week I bought two 15 PSI caps from Pepboys and YES is does cause problems. I was driving on the highway and suddenly my Temp gauge starts to spike (about half way, I have a S4). I pulled over and idled for a five minutes and my engine cooled back down. When I got home I inspected my engine and saw that the coolant hose at the back of the engine had been leaking. It’s the one that connects to the throttle body to the water pump. Hence, I tossed the Pepboys caps and shelled out the cash for the Mazda caps. NO PROBLEMS SINCE...

 

I'd be suprised if an extra 2psi caused this problem. More likely the cheap cap actually allowed more than 15psi...

 

On the S4 only one cap should be the spring loaded type. Are you sure that's not the problem?

On another note, I would wonder about the condition of the hoses.

 

Easy answer to why they sell higher psi caps... money! There is enough dumb@sses in the world that would go out and buy a quick fix than spend the time and money to just fix it right the first time.

It can't be helped... some people in the world are just idiots.

 

hey, I found out something that NZ didn't know! Thats one down, 3 to go!

But yea, just for confirmation, higher PSI caps are just a money grabber?

 

it's not a money grabber, increasing the boiling point is useful.

you can run a mix with more water and increase the boiling point with the upped pressure which the antifreeze would normally have done.

increased pressure will also help prevent localized boiling @ hot spots in the engine.

 

You shouldn't be anywhere near the boiling point of water at 13psig anyway (~246degF), and running with reduced coolant will resuslt in corroded engine internals.

If you can't keep your enigne cool with a 50/50 coolant mix and a 13psig cap then something it wrong. Either something needs to be fixed or you've reached the system's capacity and should upgrade.