STI radiator cap

[KungFuMonkey]

I have seen some members replaced the stock .9 bar radiator cap with the sti or some other after market cap with 1.3 bar. What is the benefit of this? I have to replace mine, should I go with the cap that holds more pressure? or is the cap mostly for bling?

[AussieDan]

I hadn't thought about this too much, but a little googling turned up some info:

http://www.enjoythedrive.com/content/?id=10504
http://www.absoluteradiator.com/Radcap.htm

So I guess in theory the higher pressure cap will give you a little more headroom if you're running the car really hard and the temperature spikes above the boiling point of the lower pressure cap. Other than that there doesn't seem to be that much benefit, and you could burst a hose if they're not up to dealing with the higher pressure.

So basically right now the car would start boiling coolant if the coolant temp reaches 212F, whereas with the 1.3bar (19psi) cap the boiling point would be closer to 230F (I'm fairly sure the calculation on the 2nd link above is wrong). So with the 1.3bar cap you'd raise the temp at which the coolant starts boiling by roughly 18F, and increase the max pressure in the system by 0.4bar (5.9psi).

[overl0ad]

I have seen some members replaced the stock .9 bar radiator cap with the sti or some other after market cap with 1.3 bar.?

i've replaced mine stock 1.08 with the Sti 1.3.

expected to experience longer wait times for warming up, but seems to be no different.

there are a few different pressures out there that i know of.

0.9
1.1 (1.08)
1.3
1.5

i took the option of actually going to STi and buying mine as i was worried that the ones u get on ebay may not actually be what they claim to be.

from memory, if u go to a 1.3, you are actually putting the setup at 2.3. this is as you add 1.0 for atmospheric pressure.

[Navig8r]

So basically right now the car would start boiling coolant if the coolant temp reaches 212F, whereas with the 1.3bar (19psi) cap the boiling point would be closer to 230F (I'm fairly sure the calculation on the 2nd link above is wrong). So with the 1.3bar cap you'd raise the temp at which the coolant starts boiling by roughly 18F, and increase the max pressure in the system by 0.4bar (5.9psi).

Actually, Water, not coolant, boils at 212F. Since none of us are running straight H2O, the boiling point is higher. This is a good thing, or we would be running on the brink of boiling most of the time.

It seems to me that running a higher PSI rated cap only increases the chance of damaging some part of the cooling system.

One thing to do before changing a cap would be to actually pressure test the cap to see if it is functioning correctly.

[Wiscon_Mark]

180* really isn't that close to boiling.

[Reason]

To really gain any benefits I was going to get an aluminum radiator by Koyo, STi cap (I have) Crucial 160 t stat ( I have) Cusco radiator shroud (I have) and some of that coolant additive by redline. I was doing all this because I was planning on a wrx swap and eventually an STi short block.

But on your temp gauge you won't see a difference with just the cap alone. Something like that is minor alone but key in the grand scheme of things.

[Wiscon_Mark]

lower thermostats are really a waste...

[Reason]

lower thermostats are really a waste...

Of course they are...

[Wiscon_Mark]

lower thermostats are really a waste...

Of course they are...

Tell me what you hope to gain from a lower T-stat considering you'd be moving the engine out of it's optimum operating temperature.

the only way I can see it being beneficial is if you're running an engine where the stock radiator can't keep up...but that's only delaying the inevitable.

[Reason]

If you read my post you would notice where I was changing the radiator.

You know I'm just going to leave it alone...

[Wiscon_Mark]

If you read my post you would notice where I was changing the radiator.

I still don't see the point.

I'm not trying to dig at you personally, I'm just wondering what your reasoning was, if any.