Most of the hoses for the cooling system of the 300SEL appear to be original, or quite old.  I wanted to replace these hoses with ones that looked original, or at least were the current Mercedes part.  Searching through the EPC to gather part numbers was rather useless.  There were many different part numbers for hoses that appeared to be the same, and nearly all of the part numbers turned out to be bad.  With the help of the classic center, I was able to come up with some length of hose in the necessary sizes.  For future reference:

  • 38mm: N 900271 038025.  This 38x46mm hoses is used on the thermostat housing.
  • 18mm: N 900271 018038.  18x27mm hose used for the heater connections
  • 12mm: N 900271 012018.  12x21mm hose used for several connections, including the injection pump and fan coupling thermostats.
  • A 340 501 02 82.  The upper and lower radiator connections use this short funny hose with a large bulge in the middle.
  • 46mm+: The connection from the water pump to the radiator is larger than the 38mm hose I had.  I still need to figure out the correct size for this one.
12mm Hose
12mm Hose, old and new

Today I managed to remove all these hoses and replace most of them.  You begin to appreciate just how complicated the M189 when you work on it.  There are a lot of hoses.  There are several very short pieces of 12mm hose associated with the fan coupling thermostat which are very difficult to get to.

I ran into a snag when I realize I didn’t have the right size hose for the large water pump connection under the manifolds.  Since I had already removed the old hose and the car would now be laid up until I could get the right size, I decided to take things a little further.

Looking through the radiator cap, I could see the core was pretty crusty looking.  So I pulled the radiator out and will have it cleaned up at a local shop.  While its out, I’ll have easier access to change the belts and and address the oil leak at the front of the engine.  Still lots of work to do!

Radiator Cap

One of the difficult things when working on old cars is finding the right parts.  Even when they’re available, its not immediately obvious what is correct.  Since I’ve had the engine running, I’ve noticed cooling water leaking out of the radiator’s cap.  Although the cap looked good, I decided to order up a new one and see what came.  The new part wasn’t what I was expecting, but makes perfect sense.  These pictures show what was on the radiator on the left, and the new part (A 000 501 19 15) on the right.

000 501 19 15000 501 19 15

The issue is the way the expansion tank, which is unique to the sedans, is connected to the radiator.  There is a small hose running from the tank to the overflow connection on the radiator.  This means that any pressurized water in the expansion tank was pushed out of the radiator’s cap above the rubber seal.  The new cap seals at the top of the radiator, closing the system and allowing pressure to build.  The cap that is on the expansion tank is more like the one on the left (although its a larger size) and uses a spring to hold pressure in the system up to a point.

So, another minor problem solved!