Performance radiator caps?
 

I was wondering if the "performance" radiator caps actually do anything. Do they keep you car running cooler or do they make it run hotter? I have never known anyone to have one so just wondering. While I'm at it, where can you get a black magic electric fan? Thanks alot.

They keep the fluid in?! Its only a cap...

Are you just assuming this or do yiu have a "performance" one? They sell a GReddy one on rx7.com & I was seeing if they keep your temperature down or what. I have heard from someone somewhere that they give like 2 or 3 extra HP, but I would like to know some facts or reasons why it would give you more power.


And by the way, it doesn't just "keep fluid in." The cap is pressurized. The performance ones give more pressure.

Yea, it just lets you build more pressure in the radiator and therefore run a higher temperature before the pressure overcomes the spring in the cap and you spew.

The GReddy cap is 18.5 psi. I don't know what a stock cap is rated at, maybe 15 psi.

Here it is:

http://brfoundation.com/RX-7/Images/greddy-rad-cap.jpg

Be careful though, you might get this if you have a high mile radiator:

http://brfoundation.com/RX-7/Images/radiator.jpg

Stock is 0.9 bar (13psi). Someone just a while ago recommended against running a higher pressure one on a stock setup, because of the added strain on all the cooling components (including the coolant seals in the engine).

-Tesla

Ok, changed my mind about getting one. One question though...why would you want to raise the psi? I thought it would lower it to run cooler?

That's because of the way thermodynamics works. :) When you pressurize a liquid, it raises it's boiling temperature. That way, the coolant can hold (and therefore dissipate) more heat. If you pulled the cap off when the engine was hot (DON'T DO THIS!), hot water and steam will fly out and burn you. However, with the cap on, it's all still in liquid form inside the system. You want it in liquid form because:

(a) takes up less space

(b) Transfers heat better

A higher pressure system would work a bit better.. But the 13psi ones we have do just fine for us.

-Tesla

yeah my friend bought a nismo rad cap for his sr20 silvia
and then while he was running on the freeway, the radiator just blew.. he didn't notice the nismo cap had a higher pressure than stock...so make sure it's safe and then do it...but if u wanna raise pressure to make heat transfer more efficient, forget about the cap..just go for a aftermarket radiator..by the way my friend was racing a del sol....

and tesla r u a Mechanical engineer?
ur reply totally reminds me last yr in my thermal class...
i had enough of it already...

anyways..u r absolutely right...higher pressure will have a higher boiling point..which makes a lot of sense why want a higher pressure...and obviously u don't want the coolant to evaporate at a low temperature...and that's why we use coolant...caz it has a higher boiling temperature than water, and lower freezing temperature...so when it's really cool...ur coolant wont' freeze like water below 0 degree C..and won't boil when above 100 degree C at atmospheric pressure.

An ME? Oh good god no! :) Computer science here.. I just paid attention in thermo.. ;)

-Tesla