Mystery leak...help!
 

Good Day!

!995 E320 wagon close to 300,000 miles. In my possession for nearly a decade. Just changed spark plugs, wires, coils, motor mounts, starter, coolant overflow bottle, coolant cap, thermostat...just spent $400.00 at Pelican parts last week...car runs really, really well.

Problem is I have to add about a quart of water every time I drive it to work, which is twenty miles. Whenever I stop after a drive, there is always a puddle under the passenger side. No temperature rise and not radiator light ever.

I had to replace the dreaded Y junction by the brake booster last week after it blew, but I don't think it had anything to do with anything as it was leaking before.

I now carry two gallons of distilled water wherever I go.

Is there a secondary reservoir somewhere under the car that I don't know about?

Thank you in advance.

Possible leak from hose that runs through the firewall into the heater core?

You could have an overflow bottle under the front wing at the rear of front wheel arch liner. Now please let us know if this is the M103 lump? . The W124 had this bottle but i am not sure about your 190e . If you put to much coolant in it will exit in to this bottle we talk about under the wing . The coolant should only be up to the join in the expansion bottle on the inner wing , thats when thev engine is cold . My bottle is under drivers wing in the UK .Yours could well be under same place but passengers side wing
Another place it leaks from is the rear lifting eye on the rhight hand side- at the back of the engine. Heater hoses come out of this the pipe thats fixed to the lifting eye that exits the engine and goes to the heater matrix . I will post a picture of the part it will need an O ring fitting on the end after its removed from the head . You will see if it is that leaking , by puting your hand down the rear of the engine to the place your cylinder head joins the block .It will be wet with coolant .It then runns down the bell housing and down on to the floor passengers side .Let us know if you find it .

leak
 

This is the part i was talking about .Its held on with 3 allen bolts .So ungain to remove .I refitted it back in olace later with 3 bolts, much better to remove later on if need be . I had to chissel my allen bolts out as they were corroded like the picture . Let us know how you get on please . The other place it can leak is the heater plug .

Mine is a '91 300-SEL so we are not talking apples-to-apples.
Had a similar issue once. Small plate on top of mono-valve had loose screw. I could never see it until I put a pressure tester on the pressurized coolant tank.
You may need to do the same.

Get under the car or use a mirror to look at the head gasket in the rear exhaust manifold area. My 97 SL320 ( with a M104 engine same as yours ) is starting to weep coolant there as well above the water pump.

Also have a look at the AC condensate drains, if a heater core is leaking, most cars ( regardless of brand ) will drip coolant there. Some older stuff will flood the interior though.

A cooling system pressure tester should help you find the leak. You can borrow one for net no cost from Autozone.

Sixto
98 E320s sedan and wagon

I was mixed up some place, and i was telling ismalley about the 2.6 engine m103 after i saw his 2.6 190 e picture . And not nestorb89 on his m104 . Hope you find the leak might be the water pump . Put a dye in the coolant system it will find it for you .