M104 running hot or what...?
 

At hwy speeds 75-80MPH the temperature gauge stays at 100 C constant. The ambient temperature is 93F.
It is right?
In slow trafic stays at about 95C
If the ambient temperature drops at 75-80F then the gauge stays at 87C at hwy speeds and 95C in slow trafic.
It is normal.
I was reading all the posts regarding this issue but no clue yet.
Just to mention that all cooling component are less than a year old( radiator, water pump, thermostat, fan clutch, MB fluid) The aux fans are working fine in both stages. A/C is perfect.

Give me a clue....
Everyone on this forum is claiming that on hwy speeds the temp should be rock stady 87C . Mine is not.

normal?
 

I know the M103's used to sit at 100C quite happily while cruising, Ive seen several do this. Also the M102's would quite happily sit at this temperature.

Heres one thing to try.

Run the car at stand still and watch the temp guage. It should rise and at about 100C or so, the fans should cut in. Then cut out after a couple of minutes. The fans should cycle on and off, but not stay on.

Also when you sit in traffic and the temp rises, when you move away does the temp drop? if so then all is well.

Temperature you listed are within MB specs but at the same time, something is wrong. Temp on the highway should be lower than slow traffic temperature.

I exactly the think I am asking for. The hwy temp is the one that puzzels me a lot. And as I have mention earlier all cooling system components are checked and came out fine.

High temp at highway speed is indication of inefficent radiator cooling ..
Separate the radiator from the condensor on top and see if you have lots of dirt/blockage in between .. a good cleaning with a garden hose works here.. then retry..

also , check all 4 wheels after a run for heat [ dragging brake possible]

also check coolant a/f mix %. You do not want more than 50/50

100C at high ambient is not out of spec, but a thermo that does not fully open will also do this .

im definitely guessing some sort of blackage. at high speeds you are working the engine harder so it will create more heat, albeit you get more air through the radiator..
at lower speeds, there is less airflow, but less heat as well.
that you have higher temps with higher airflow indicates a blockage to me.

clean out your radiator of leaves, debris, insects, anything.

Temp got up to 98F today in South Jersey and I was driving on the hwy and the water temp was constantly at 100 C even at 105 C but the aux fans cooled down. I was checking tthe radiator but no blocked radiator, fan clutch is good, system holds presure, antifreeze is OK 50/50, all looks to be ok but the temperature. By the way radiator almost new, water pump 70K.