After a while of noticing that the coolant temp gauge in my 97 C280 never goes above 95C, i began to get suspicious. So, I removed the aux fan fuse and let it sit for a while. Now, the mechanical cooling fan can do a good job cooling the engine, but when it is sitting at idle for an extended period of time on a hot day without the help of the aux fan, it can't meet all the airflow needs of the engine. I knowing this decided to experiment and monitored the actual engine temp with the live data feature of the climate control unit and compared it to coolant temp gauge in the instrument cluster.

Here is what I found: Temp gauge functions normally up until the needle reaches 95C. After that, the needle seems to be programmed to stay at 95C regardless of what the engine temp really is. I watched as the actual engine temp very slowly climbed up above 100C and the needle still stayed on 95C. In fact, the needle stayed on 95C until the actual engine temp reached 115C. Then the needle rapidly shot up in stages, first to 100C, then to 110C within a matter of seconds. At this point, I shut it off and put the aux fan fuse back in and let it cool off. So, whenever the actual engine temp is within a range of 95C-115C, the coolant temp gauge shows 95C no matter what. The coolant temp gauge functioned much as the coolant temp gauges in Japanese cars do. It stayed in the "normal" range regardless of actual engine temp then rapidly rose when it was almost too late.

Needless to say, I was disappointed. I guess Mercedes decided much like many other car companies that they didn't want people complaining that their car is overheating because it reaches 100C (which is normal), so they decided to program the gauge to function like an idiot light.

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

what's next?

plastic hubcaps and vinyl roofs?

no, no, hubcaps-by-wire
gps guided vinyl roofs
with xenon opera windows

that's so MB 21st century

I am glad I have an old car.

Actually, plastic wheel covers were quite common on the w201..

Yeah , say good- bye to accurate temp sensor unit circuitry.
After 1996, they went with new sensors [ Motronic]
Combined the gauge sensors with the ECU operation..

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1K51DMBHN1K51EQC67&year=1996&make=MB&model=C-280-001&category=P&part=Water+Temperature+Sender

Same change to all other models? No wonder my water temp needle never moves..

Motronic

One more reason to keep my '94 wagon, I like watching the temp needle waffle between 95C and 105C depending on where and how hard I push it.

__________________
dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles

What's next, a voltmeter instead of an ammeter to display charging circuit function?

There are times when a volt meter is a better system monitor than an amp meter , but both would be real nice [ Wishful Thinking]

..Soon, that might be all we have on the dash.. two electric meters

When would the volt meter would be better?

I prefer the ammeter (actually a galvanometer with a shunt ) because it shows the dynamics of the battery.

Right after a start, it would show the charge being put back into the battery.

When the alternator had replaced the charge 'borrowed' from the battery, it read zero all was right with the world, neither discharging or recharging, as the alternator supplied all of the power needed, and the battery 'floated' along.

At idle, with the headlights, defroster, etc. it might show the battery discharging to supplement the lack of alternator capacity at low rpm. It would show charging again as the rpms picked up, and again level off as the charge was replaced.

A weak or failing alternator showed up as a (-) or Discharging long before the battery voltage dropped and the battery failed.

Our Suburban has a voltmeter that says any voltage between 9 and 14 volts is "Good."


Best Regards,
Jim

< >>

When monitoring Bat voltage, not charging rates...
That is why both are best and many add one or the other , depending on what is there to start with.
An Amp gauge will not always tell bat condition or valtage.
You can only assume bat condition with an amp gauge...

Ali,

That was a great informative post.


Scott
1998 C230

Thanks. I initially always thought that the coolant temp gauge truly reflected the engine temperature. So, if the car is going to overheat, it won't let you know anything is wrong until the temp goes above 115C. By then, its not too far away from overheating and doesn't give you a whole lot of advance warning. If you really want to see the engine temp, I guess you have to pull up the live data on the climate control unit.

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

Most of the motronic units, whether BMW or MB do this of keeping the temp essentially in the middle when its in their acceptable operating range.

My old 190E's used to show real time wild temperature shifts. Initially it worried me, but I got used to it. My BMW never, ever, flinched from the middle of the gauge. My w202's seem to flinch a little bit, but not anything significant. Anything out of range on the high side, and shut it down immediately, do not wait. Pull over at the first safe opportunity and shut it down. You do not want to warp a head or blow a head gasket due to runing the motor hot.

Anyone who is seriously concerned about real time engine operation data, needs water and oil temp, as well as oil pressure. But these arent exactly cars for the most part the general public drives hard.

Take care,

George

__________________
George Androulakis

Former Mb's:

1990 500sl R129 - 76k Original Miles - New project - Follow the saga http://90r129.blogspot.com/
1990 190E 2.6 148k mi (sold)
1989 420 SEL 246k mi (sold)
1995 C220 175k mi (sold)
1992 190e 2.6 74k original miles (sold)
2000 c230 Kompressor 122k miles (RIP)
1996 C220 149k mi (sold)
2000 C230 Kompressor Sport 127k (sold)

Current Cars:

2009 Mercedes c300 4matic
2006 Mercedes s430
2005 Jaguar XJR
2003 Cadillac Escalade