Physics is physics, Mike. The "laws" of physics don't change.

Suit yourself, but there is are reasons for using glycol as coolant, and boiling point elevation is a bit one.

Peter

Is there a measure for the 50/50 ratio? Such as when the coolant is tested for how low its freezing protection goes?

A bit more on topic, I just have gone through overheating problems on the 91 300e. I had replaced the thermostat 6 months ago and the radiator was rebuilt 2 years ago. I couldn't figure it out.

Finally I replaced the radiator and Tstat and all is well.

Haasman

How many miles are on this car, and what model motor?

<<Is there a measure for the 50/50 ratio? Such as when the coolant is tested for how low its freezing protection goes?>>

A 50/50 mix will show as a protection of minus 37C [ -34F]

Thanks Arthur .... it seems all of my cars are off in the coolant ratio .... I've had the mix give protection to -10 degrees F.

Haasman

You are a little light in the mix
Benz like to see a min minus 30C [ -22F] . which equates to 45/55 af/H2o.
Reasoning is both corrosive protection and boil point specs.
Your car actually left the factory with those specs.
On the other end , the heat transfer deminishes to the point of possible warm running conditions at 65/35 ratios.

My own thoughts are hot climates [USA] can be 40/60 with good overall results...and 50/50 for normal Winter Belt geographic areas [ USA]

Hi all,

A Merc will NOT overheat unless there is something wrong with the system. I live in the tropics and have had similar problems. In fact it was dealer induced. The water pump failed and after they replaced it (before this it was always steady at just under 90C) the temp soared almost up to 120C--- Not funny. I took the radiator apart and cleaned it - no difference. I finally decided to take the thermostat out and check it in a saucepan BUT the dealer had removed the working parts of the thermostat without telling me!!!! Got a new thermostat and PERFECT! Back to normal. DO NOT EVEN THINK OF REMOVING THE THERMOSTAT !!! It is needed to do the job.

It sounds to me more like a water pump problem - I would check that first and then go on to the thermostat. After that flush and clean the radiator.
Mine is not overheating at all now in spite of the fan clutch not working properly (I can actually stop the fan with my finger even when at operating temp). (BTW Don't try this unless you know what you are doing...)
Other things that cause extra heat is late ignition timing but then you would also experience sluggish performance.

Good luck with it!!

Tom