Coolant help and WaterWetter notice

[BENZ-LGB]

Now that summer is here, I want to change the H2O to coolant ratio in my 420SEL and in my daughter's 300TE to a 55/45 or even 60/40 H2O/coolant ratio.

I bought one of those nifty Prestone coolant gauges and tried to use it but alas! the markings in the guage only have boiling point readings and not ratios. The only "clue" they offer is that a 50/50 ratio offers boiling protection up to 129 degrees C. That figure is good for a 15 PSI radiator cap (about 103 in metric, but Mercedes uses a 140 cap).

I suppose that I could try to extrapolate forward or backward from that point (taking into consideration the different cap pressure). But not being mathematically gifted (that's why I am a lawyer, I can only count the really big numbers ) I was wondering if there is an easier way to convert boiling point markings into water/coolant ratios? does anyone have a handy-dandy chart available? Or is there a gauge out there that already comes with ratio markings?

Thanks

For you WaterWetter fans out there, Pep Boys is running a sale on this fine product. (I personally would NEVER set foot inside a Pep Boys store "Someone" who doesn't mind being seen inisde a PB store told me about the sale ). The sale price is $4.88 per bottle. It usually goes for about a $1.50 higher. Time to stock up!

Have fun.