93 400SEL running hot
 

I've got a 93 400SEL that's running hot. I've replaced the radiator, fan clutch, thermostat, verified that the cooling fans are working along with the aux. pump. The engine runs great and has no water in oil or any back pressure in tank, so I'm pretty sure there is no head gasket problems. The next thing I'm looking at is the water pump. Even though it has no leaks or bearing problems, I'm concerned about the impellor slipping or not turning at all. I'm wondering if any body has heard of this problem before, and if you think this is possible. Thanks for any help on this matter. J.C.

How hot ?
We'll take it in Celsius or Fahrenheit. ;)

It seems to me there was a similar thread recently with some good information - on that motor, maybe an E420.

It will get into the red on the gauge and boil out the coolant tank while at idle.

It will get into the red on the gauge while idling, quicker if you run down the road.

I would start the engine cold, and keep feeling the upper rad. hose, looking for the thermostat to open ( I know,...it's new ).
Secondly, when the upper hose is getting warm ( hot ), feel the radiator & see if it heats up evenly ( I know,....it's new ).
Report back after this test. ;)

change the radiator reserve cap, thats your only problem (if all the symptoms you mention are right.

93 400SEL running hot
 

Well I finally got the water pump off and believe it or not the impeller behind the pump fell out in 5 pieces. It's even a metel impeller, and found nothing in there that would cause it to break. All I know is the mystery is over. Thanks guys for you're help