[kkalish009]

I've noticed the engine operating temperature is almost 100 degrees. However, as the car comes to a stop, I notice the temperature increase to almost 110 degrees. The temperature outside was around 65 degrees. Is this normal? Because in other mercedes that I've driven the highest I've seen the engine temperature at is around 90 degrees.

 

[tuttebenne]

The engine should run somewhere around 80 degrees C, give or take the accuracy of the gauge and the condition of the cooling system. There are a couple of things that will cause this in a 400e once you confirm the normal stuff like low coolant and thermostat are ruled out. (edit: I should mention that you don't want to d&ck around figuring this out because it ain't cheap to fix an overheated M119 motor)

The fan clutch is a possible cause (not turning sufficiently when the engine is running at idle or low speeds)

Also, you might want to consider the radiator as a suspect too.

Run a search on this site for info on the clutch. They seem to be rather expensive so you want to do as much as you can to pinpoint it as your problem before replacing it. A Radiator should run $200 or so and it isn't too difficult to replace.

 

[kkalish009]

I recently had my coolant service and the thermostat was replaced, so those two can be ruled out. Could a faulty low coolant sensor cause the higher operating engine temperature on the gauge?

 

[ps2cho]

Sounds like a radiator is blocked internally/externally, the pump is weak, or VFC is non-functional. 65deg ambient means something is very wrong! You should by no means be anywhere near 100C at those ambient temps.

Here in phoenix at 115F, my wagon stays at 100C during traffic with A/C on -- that's about as worse as you can give this cooling system.

 

[kkalish009]

Sounds like a radiator is blocked internally/externally, the pump is weak, or VFC is non-functional. 65deg ambient means something is very wrong! You should by no means be anywhere near 100C at those ambient temps.

Here in phoenix at 115F, my wagon stays at 100C during traffic with A/C on -- that's about as worse as you can give this cooling system.

I think the water pump is the original one (meaning its got 19 years and 176k of use). So it could definitely be the pump. If so, do you think it will be okay to drive the car in winter and by the time spring rolls on by I can then replace the pump (I'm assuming $1K+ for pump & labor)?

 

[tuttebenne]

For what its worth, the pump would be the last thing I would suspect. Usually a pump will either work, leak because a seal has gone south, or fail because a bearing has let loose.

 

[macdrone]

Pressure loss through the expansion tank cap or either end of the hose that connects with the small line from expansion tank to the radiator. I would check for hairline cracks there first. The plastic ages and the tank gets a crack and the radiator neck get brittle and also cracks. Pressure loss causes boiling which makes the temp spike. Also at 110 sounds like the Aux fans are not coming on? and the viscous fan could be bad also. The 400E M199 is a heat pump engine but the idea to keep it cool is simple, hold pressure to not allow coolant to boil, move it around the block till it gets hot thermostat opens and lets cool water in, fans cool the radiator to allow there to be cool water.

Good Luck.

BTW I had that problem, it was the AUX fans, expansion tank and radiator all needed replaced I just spread it out over a year cause each piece I replaced made it a little better.

 

[sbaert]

I'd likely consider the fan clutch and radiator as high on the suspect list, followed by the water pump. With the engine idling, check/feel the upper radiator for a pulsating. If you feel the pulse, then the water pump is likely good. If not, the impeller might be loose and not pushing enough coolant through the engine block into the radiator.

Also don't discount the possibility that maybe the wrong thermostat could have been installed.

 

[kkalish009]

tutte- the car behaved better in the afternoon; the water temperature was around 90 degrees, still above average from around the normal 80 degrees, but definitely better than the 110 i witnessed on the highway this morning.

mac- basically, when i start the vehicle, the aux fans in front of the grille/hood should be moving, correct?

sbaert- i will definitely give your suggestion a shot thanks. as for the wrong thermostat, the water temperature was still hitting around 100 degrees even before i replaced the thermostat so im pretty sure that the correct thermostat was installed.

Thank you everyone for your input; greatly appreciated!

 

[LeftCoastGeek]

on my 300E2.6, the electric fans only start when the AC is running and its rather warm outside.

 

[tuttebenne]

on my 300E2.6, the electric fans only start when the AC is running and its rather warm outside.

Essentially that is correct.

One of the things to watch for is that with an aluminum radiator and aluminum heads and water pump, there is a lot of aluminum in suspension in the cooling system. This bonds to the radiator channels and although the radiator may look pristine inside, it can be blocked. With an M119, an original radiator should be chucked as a matter of maintenance and insurance.