W210 Interesting Temp Guage Factoid
 

I was browing my Startek DVD looking for some information as to why my Coolant Guage in the instrument cluster and the Temp readout in the HVAC controls were different. Heres what I found regarding the ECT Guage

" This display (guage) is a plateau display. i.e. the pointer stops at 95 degrees C. at temps between 95 and 115 degrees C. Temperatures in this range are still not critical. The correct temp is only displayed again from a temp. of 116 degrees C. This prevents the driver from being disturbed by the display, for example at high outside temperatures. The warning rage starts at 116 degrees C. The coolant temp signal comes from the engine control module."


I know my Passat was that way but I thought the MB was an actual reading. I guess I have to be "disturbed" by watching the HVAC module with the temps. incrementing from 88 to 105 depending on speed, ambient temp., and how long the hill climbs are.

...A shame Benz had to go that direction simply b/c of owners misconceptions and worry over of the variable Thermal Heat Loads encountered in a water cooled engine.
We used to see so many threads concerning the Benz temp gauge being compared to the Asisan Imports of the World... [ " My Honda stays right there all the time, never flinches !! " ]
I personally prefered the Correct temp displayed....
...Placebo Gauges...

My '96 does not act this way. What year is your car?

Mine is 1997. the guage does move freely from 88 to 95 but never goes past 95 even when the HVAC temp is saying its 105 C engine temp

I monitor the CCU coolant temp on hot days. Its never gotten above 213f. I'd swear the dash temp gauge read 100C at that time.....?

Maybe it was only for the 97 model year, as the Startek DVD is model and year specific.

I believe the gauge circuits got changed when they started using the Motronic temp sensors. The last of the single wire/circuit water temp gauge
senders was HFM/SFI. Those used a seperate gauge sender and were direct redings [ non-dampened]. The newer ones used the ECU temp input sensor signal to also run the gauge.

This single wire is the earlier/seperate circuit sender used on HFM:

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FG17RJ3A2FU0VDD8E&yearid=1995%40%401995&ma keid=MB%40%40MB%40%40X&modelid=E%2D320%2D001%40%40E+320+Sedan&catid=P%40%40Body+Electrical&mode=PA&s ubcatid=P4036@@Water+Temperature+Sender&source=www.peachparts.com&clientid=catalog.mercedesshop

Here is later used on Motronic:

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FG17RJ3A2FU0VT6YT&yearid=1996%40%401996&ma keid=MB%40%40MB%40%40X&modelid=E%2D320%2D002%40%40E+320+Sedan&catid=P%40%40Body+Electrical&mode=PA&s ubcatid=P4036@@Water+Temperature+Sender&source=www.peachparts.com&clientid=catalog.mercedesshop

AFAIK, most cars are designed this way...the temp gauge on my Supra is dampened, and stays in the same spot all the time, unless it gets REALLY hot, then it immediately shoots up to the red, and by that point it's usually too late... :(

213F = 100.6c

Exactly....the gauge did not read 95C.

My CCU display also reads out in F whereas the OP reads in C. Fairly common with W210's of this era.

BTW, where is the temp sensor on this engine (OM 606) and is there a separate sensor for the gauge and the computer?

I believe the damping circuit will still show correct temps, but they dampen out the quick changes one will see . as like coming off a high run to a stop. etc....that would be the damping circuit , whereas the seperate sender circuits report back exact changes immediately..[ non-dampen temp readings]
The single sensors is completely independent of any other circuits [ non-integrated] and is a simple temp gauge [ volt meter] with a ground signal thru a thermistor.

The later dampen style have a temp sensor that intergrates all coolant temp inputs into the motronic IC Input for distribution and is used by different systems.

That is why HFM had so many temp sensors and Motronic has one.