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  #1  
Old 07-06-2000, 09:29 PM
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Join Date: May 1999
Location: Charlotte, NC, USA
Posts: 688
Have had this question nagging me for some time and no one I've questioned had THE answer as MB would.
A while back, Mercedes would use radiator caps with the marking '100' on them. As engine temperatures rose due to better burning and emmissions the caps were changed to '110'. The latest versions are now reading '120'. What do these markings relate to? Or is it some DIN...Deutschland Invented Number?

Tobias MB
300SE, 300CE, C280Sport, 190/5.0
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  #2  
Old 07-06-2000, 10:32 PM
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Join Date: Mar 2000
Posts: 529
Actually, the latest version is a 140 (#124 500 04 06). The cap number is a multiplicative, refering to the pressure at which the cap will open to blow off excess system pressure: the "100" cap opens at one atmosphere; the "120" cap, at 1.2 atm; and the "140", at 1.4 atm. These later caps permit engine cooling systems to run at higher pressures, thereby elevating the boiling point of the coolant.
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Old 07-10-2000, 09:41 PM
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Join Date: May 1999
Location: Charlotte, NC, USA
Posts: 688
jgl1, Thank you for replying and passing along the info. I have since been to our local public library and researched deeper.
Following is a chart showing the effect of pressure on the boiling point of water:

Pressure(kPa) Boiling point: 'C 'F
47 80 176
68 90 194
100 100 212
140 110 230
195 120 248

This chart shows how much higher the boiling point is with the newest style cap available,
as long as the plastic tanks stay in place!
Since all Mercedes are water cooled, I think all owners would be interested, especially during this warm summer.

Tobias MB
300SE, 300CE, C280Sport, 190/5.0

[This message has been edited by Tobias MB (edited 07-10-2000).]
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  #4  
Old 07-10-2000, 10:11 PM
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Join Date: Apr 2000
Posts: 117
re: the previous post's "...the effect of pressure on the boiling point of water:
Pressure(kPa) Boiling point: 'C 'F
47 80 176
68 90 194
100 100 212
140 110 230
195 120 248..."

Be careful! You have to remember that the pressure in the system is going to be that cap pressure (where "100" = 1.00 Atmosphere, or Bar) OVER ambient atmospheric pressure (which is 1.00 Bar at sea level, and a little less up in the mountains"), so that chart might be a little misleading to a lay reader who doesn't know to add ambient pressure to the system's pressure determined by the cap's release rating.
Example, that chart taken literally, using the cap "100" could mean sea level pressure -- same as ambient -- and thus offering no retention of pressure at all at sea level. In fact, the cap "100" allows for one atmosphere of pressure OVER ambient pressure (before releasing), or actually TWO atmospheres of pressure within the cooling system.
In other words, your chart implies that a "100" cap allows water to boil at 100 C or 212 F, whereas, in fact, that "100" cap will permit the coolant to rise to about 120 deg
before boiling, the equivalent of TWO atmospheres.
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