Anti freeze serves several purposes, in addition to it's name.
It also acts as a rust inhibitor, so slows down corrosion.
Anti freeze also raises the normal boiling point of water, so instead of turning to steam a 100 C at normal atmospheric pressure, it has a much higher boiling point, depending on the strength.
Add to that, in a pressurised system, the boiling point will also be increased, hence in a pressurised system, if you release the rad cap quickly on a hot engine, the hot water turns instantly to steam.
So my thoughts are... the system is not holding pressure, using standard water under these circumstances will encourage water loss.
If you do have a leak, if it is plain water, it can evaporate and won't leave a deposit, so you won't know where it is leaking. You may only have a small leak, one drop of water a minute adds up over time, and won't be that obvious.
It might just be a simple case of tightening those jubilee clips.
If there is anti freeze in the system, if there is a leak, you will see some residue in the form of crystals.
So my recommendation, always use the correct grade of anti freeze, 50% gives the best overall performance.:thumb2
As suggested, there could be leak past on the rad cap.
Doesn't sound too much of a problem, but running with low levels of coolant will create more problems.
My 1995 Mav bottle stays at the same level year on year, in fact I never add any water between anti freeze changes. BUT one winter, I did see a puff of steam, when in a queue, on inspection, it was a jubilee clip on the top rad hose, a 1/2 turn later with a screw drive ... sorted. The hose compresses over time as they age, and can cause leaks.
Hope it helps,
best regards,
Rustic
