Radiator caps

[ja17]

I noticed that many vintage Mercedes cars including the W113 cars have the wrong radiator caps installed. All W113 cars should have radiator caps marked "100" (actually 1.00). Many of you will find an incorrect  "120" or "140" (1.20 or 1.40)radiator cap on your car. the caps look identical except for the important pressure rating.

The "100 (1.00) radiator cap will allow your cooling system to pressurize to the designed pressure of one atmosphere (1.0) or 14.7 psi.

If you have the 120 or 140 radiator caps fitted to your car,  your cooling system will over pressurize to 17.44 psi. or 20.58 psi. !!
Way to high for a W113.


Joe Alexander
Blacklick, Ohio

[Tom230sl]

great tip, will take a look at mine.. thx

[iceberg]

I don't have a rad cap. There is a cap on my rad res and it says 10o.  Is this the cap you are talking about?

[hauser]

Joe, does elevation have anything to do with this rating?  Some of these cars were sold in high elevation regions and I was just wondering if this might be an exception to this rating.

1969 280sl 5 spd
Gainesville, Fl.

[ja17]

Hello iceberg and hauser,

Yes the radiator cap is the reservoir cap on the W113 cars. As far as I know the caps were always 100 for the W113 cars regardless of altitude.


Joe Alexander
Blacklick, Ohio

[Benz Dr.]

Each lb of pressure will give you about 4 more degrees of boil over protection. So you could go as high as 270F before it would start to boil. Of course, you should never let your engine temp go that high.

 230F is already getting high enough to do some damage.
This is at sea level - C.C.R. types living at higher elevations take note on 100F plus days.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[gugel]

Thanks for the heads up, Joe.  I checked my cap, which appears to be original, and it is 100.  

However, I also noticed that I hadn't been turning the cap all the way past the detents when tightening it, so the springs were probably compressed too much, effectively raising the rating.  I don't know how important that is, but it seems worth checking also.

Chris Earnest