I notice that the water resevoir is always empty even I keep filling it up. I was wondering if there is any leak. A check finds a damaged radiator cap. I have been using this SARD 1.3 Bar (kg/cm2) cap since 3 years ago.
So I dig up the web to find the replacement; in short:
1) Radiator cap it a control valve that raises the boiling temperature point of the car cooling liquid keeping the coolant in liquid form under higher operating temperature.
2) 1.3 Bar (19 lbs) Cap: Valve open when coolant liquid hits 153 degC.
3) 1.1 Bar (16 lbs) Cap: Valve open at 127 degC.
4) 0.9 Bar (13 lbs) Cap: Valve open at 100 degC.
Naturally most people will choose to have the 1.3 Bar (as what I did before) which result that the coolant can still remain in liquid from at 153 degC (radiator + cooling system can operate at higher temperature before valve opens).
In actual condition of normal street driving (some short sprint) we rarely hit water temperatures above 120 degC. For track, it would be different story/game as we tend to push the car at the limit for long time. So for me, I downgraded the Cap from 1.3 Bar to 1.1 Bar.
1) I do not need my car cooling to work at 153 degC, if it does then the cooling system is need to be changed (Radiator, hose, water pump) to lower down the temperature (operating at high temp is NOT good for your engine due to possiblity of parts wearing to knocking issues).
2) The radiator cap does not help to improve the cooling rate of the system temperature, it only force the system to work at higher temperature.
3) The car cooling system efficiency improvement requires upgrade of High capacity Radiator, Silicon Tubes, Bigger water pump, better Fan + etc (basic items).
4) Very important... it is CHEAPER! :) LOL!
Note: Using a high pressure CAP in normal system and if the temperature ever hits above 140 degC; it would be a problem as the system is operating a over temp and component wear will be critical, the tubes may burst causing a disaster if you are pushing the car hard. Using a lower temp 1.1 Bar is safer as the raditor Cap only permits the system to be operated at max 127 degC.
(0.9 Bar is not really commended as it too close to normal operating temp, causing the valve to open too early and reduce the cooling capacity at normal use).
It is highly recommended to install an after market Water Temp meter to know exactly how hot is your engine coolant is running. (Below 100 degC is good, best at 90 degC but almost impossible to hit at hot days) (Above 100degC needs caution; and if it ever goes to 110~120 degC, it is better to slow down the car at "lower rev" and let the system cool)