hello list,

sorry, this is a *really* basic question:

94 S420. Coolant light is coming on.

I've taken a look at the coolant reservoir. I can't make heads or tails of it, though - where do you find the min and max marks!

Also, do I need to buy the expensive mercedes-approved stuff, or is there a generally recognized acceptable replacement?

Use Zerex G 05 (Same,Same as Mercedes Coolant). ONLY Two Choices!

I always fill the system until the level is equal with the seam (Top to Bottom)
of the Tank.
(There is an Extension Tube [metallic] that is above the Level Sensor location
inside the Tank.It's part of the Metal Hard Coolant line entering the Bottom of
the Tank.)

Attached Thumbnails

 

__________________
'84 300SD sold
124.128

If you remove the cap on the expansion tank and look straight down you will see a plastic tab protruding from the corner of the tank. The correct level is when the coolant is at the top of that tab.

There should be an arrow pointing to a line with the word 'Kaltwasserstand' above it- this would be the cold water level in the expansion tank. On my cars this line is just above the seam between the upper and lower parts of the expansion tank.

__________________
'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)

There's no arrow on the 140 expansion tanks showing where the coolant level should be. The tank is black from the seam up; it's not transparent. The only way to determine if the level is correct is to open the cap and see where the coolant level is in relation to the tab in the corner. The proper procedure is explained in the owner's manual.

Here are some pictures of the 140 expansion tanks for those that are interested:

http://catalog.peachparts.com/ShopByVehicle.epc?q=1994-Mercedes--Benz-S4--0-Cooling--System&yearid=1994%40%401994&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6436%3AMBC%7C1532%3AED%7C10000069%40%40S420&catid=240909%40%40Cooling+System&subcatid=240916@@Expansion+Tank&mode=PA