Radiator caps and pressures

[jarrenowen]

i see a lot of people running sti radiator caps on both the radiator and the overflow, which are rated at 1.3 bar.
the stock round cap on the radiator is rated at 137kPa, and the one on the overflow is ratef at 108kPa.
just seeing if theres been any issues, why they arw rated differently and if they will have any side affects on coolant temperature or pressure.
cheers

[alexeiwoody]

i see a lot of people running sti radiator caps on both the radiator and the overflow, which are rated at 1.3 bar.
the stock round cap on the radiator is rated at 137kPa, and the one on the overflow is ratef at 108kPa.
just seeing if theres been any issues, why they arw rated differently and if they will have any side affects on coolant temperature or pressure.
cheers

Temperature of coolant is controlled by the ECU/fans. This is not affected by caps.

Caps raise the boiling point of the water based coolant, since it operates so close to the sea level boiling point of 100 degrees C. The idea is that by raising the pressure further, you raise the boiling point and retain a little more potential in the coolant system to keep working effectively, even a few degrees higher than where stock caps would have seen steam and failure of the system.

In reality, this makes little to no difference whatsoever, especially on a street car (especially times 2 - when one of your caps is 1.3 and the other 1.1 or 0.9, like most of the tbStis I've seen).

It's really just a bit of Sti bling in the engine bay then.

If you were to track the car? Might be something to consider/try, but it doesn't buy you that much more room to play with. If the car overheats? It still overheats, caps or not. A better radiator, water spray, maybe waterless coolant (not sure how well these work on the track) and a better water pump would all be much more effective at keeping a lid on (pun intended) a car that is being pushed so hard it overheats.

[HardwareBoB]

If you were to track the car? Might be something to consider/try, but it doesn't buy you that much more room to play with. If the car overheats? It still overheats, caps or not. A better radiator, water spray, maybe waterless coolant (not sure how well these work on the track) and a better water pump would all be much more effective at keeping a lid on (pun intended) a car that is being pushed so hard it overheats.

Any serious motorsport will not let you run anything but water as a safety issue, because ethylene glycol is very slippery and you'll ruin the track for others when your car inevitably pukes all over it.

Boiling points:

Fluid - Freezing Point - Boiling Point
Pure Water: 0 C / 32 F - 100 C / 212 F
50/50 mix of C2H6O2/Water: -37 C / -35 F - 106 C / 223 F
70/30 mix of C2H6O2/Water: -55 C / -67 F - 113 C / 235 F

note that this is at atmospheric pressure, at operating pressure you get another 25C or so (according to my research at http://auto.howstuffworks.com/cooling-system3.htm)

As alexei said though, it's mostly just bling - if you're cooking it on a track, you need to be looking at your overall cooling solution, which can get very expensive and complicated very quickly. Watch the following video for more information: https://www.youtube.com/watch?v=s1QpD5vY1u4


For a much better and more thorough analysis of coolant, see this page: http://hellafunctional.com/?p=629