I just got a 1999 E300 Turbodiesel that was my Fathers car for 13 years. During the time he owned it we replaced the radiator, fan and fan clutch, thermostat (all within the last year and he only drove the car about 2000 miles/year) and just today I replaced the temperature sending unit in the head. The car temperature indicates approximately 85 to 90 C around town, even in St. George Utah's 105 F temps and A/C works fine until I get on the highway and then the temperature gauge spikes up to 120C and "flickers" up and down especially on hills and the A/C compressor turns off until the "temperature" comes down a bit.

I have read the posts from 2004 and don't know if anyone was able to isolate if the water pump vane/bearing could need to be repaired. Also, when the thermostat was replaced there was alot of crystalized antifreeze. Could it need to be flushed because of a buildup scale?

Please help! I have never seen a Mercedes diesel act this way with the flickering temperature gauge and intermittant A/C.

Thanks!

One would normally advise investing in an infrared gauge to check the car's gauge for accuracy and that still is worth doing. However, the behavior of the compressor does suggest that the engine is really getting as hot as the gauge says. So first, my advice would be to not drive the car on the highway until the problem is fixed; at 120C you are flirting with danger.

If the gauge can be believed, then, it seems the cooling system is fine as long as the engine isn't working hard. When more heat is being generated, however, the cooling system can't handle it. How many miles are on the car, what kind of coolant is being used, what ratio water to coolant, and how often has the coolant been changed?

An experiment to perform: when the engine temperature is rising, as during highway operation, turn the a/c off and turn the heater on maximum. This will dump some of the heat into the passenger compartment (not exactly where you want it). Does the engine cool off a bit? If so, this confirms that the cooling system is having trouble getting rid of the heat. Since you've changed the radiator and thermostat (factory or aftermarket?), the water pump could indeed be the culprit. A system flush might also help; hard to tell at a distance.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

My car does exactly the same thing. It's scary when it flickers up to 120 degrees. My cars temp gauge will peak up to 120 but can then flick down to 95-100 in an instant. I've changed out thermostat, viscous fan, top and bottom hoses and done plenty of flushes with genuine parts/ coolant. Haven't changed the water pump or the radiator yet but will do the water pump before next summer ( winter here at the moment) and if the pump doesn't fix it, I'll do the radiator.

If it keeps doing it then I plan to start replacing temp gauge sensor and then move onto gauge itself. Unless you find an answer first..

I had that cauliflower looking build up at my thermostat also, most probably due to a lack of coolant flushes.

Good suggestion by Jeremy to invest in an infrared gun as it can rule out critical danger.

Would still be nice to get the dash temp gauge working correctly though.

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1995 E300 Diesel

1. have access to an infra-red gauge and will test when I do the heater heat dump experiment.

2. The car has 142,000 miles. Coolant is Zerex gold for Mercedes, I believe 50/50 coolant/water ratio; coolant changed 18 months or less ago.

3. I will try the a/c turn-off--though the car does that automatically when the gauge begins its climb even before the temp is between 100 to 110C. Also, at full throttle the a/c sometimes clicks off, don't understand that. Do you know what a "Citric Acid" flush is and how to do it?

Thank you for the reply. I will post my experiments/fixes as I do them so that other 606 owners will know my experience.

Just found this quote from a "Dr. Diesel" from 2004:

If you have an unexplained problem of running hot without
reason, I have seen a new issue with these turbo 606's.
I have had a few towed to me for running hot at idle, and lack
of performance. The water pump impeller (sp.) is made of plastic
and cracks where it connects to the drive shaft. Water pump can
stall out or just stop pumping. The hard part is, the pulley, belt,
and input shaft which is visible through an inspection hole will
all turn normally and be quiet. The last one was just stripped
on the shaft and was free-wheeling.
I don't know if 94-97 cars ever had these plastic pump guts.
I have never seen them on anything but turbo cars.
Usually some plastic debris ends up in the thermostadt unit, so
I always change those too.
You know us dealer guys...replace.. replace..replace.......
Dr.D

I'm going to replace the waterpump and flush the system, but would love to have anyone who knows explain a "citric acid" flush to me.

Thanks!

Here is a write up about flushing the cooling system - Mercedes Citrus Flush. I think it's a bit of overkill, but it will give you an idea of what you need to do.

On my 606 engine, I was able to get nearly all of the old coolant out via the radiator drain. I did disconnect the coolant lines going through the windshield washer reservoir though and used my air compressor to blow out the coolant in there. Then rinse once or twice. Deoiling is the first step. I used Liquid Tide, the HE version, and had no issues with soap bubble. Then descale with the citric acid. Rinse well and fill with the proper coolant and distilled water and maybe Water Wetter if you so choose.

__________________
Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles

Thank you all for your posts concerning the high operating temperature on my 1999 E300D Turbodiesel.

I replaced the waterpump. Impeller was cast iron and solidly on the shaft, but was getting pretty sketchy (squeeking, hard to turn by hand) but that did NOT solve the problem.

So I replaced the radiator, even though I had done it only 3 years ago for my Dad. What I found was astonishing and shows that you MUST drive these cars or they begin to have multiple problems; my Dad only drove this car 3500 miles in 2 1/2 years. After I had removed the radiator and allowed it to drain and dry for a week (100+ degree temperatures in Southern Utah), I compared the weight of the new radiator with the old and it was a full 5 lbs lighter!! I asked an experienced mechanic friend of mine and he told me that sometimes a misplaced/broken ground will find its way to the transmission/radiator and inject electrons into the fluid causing the radiator to act like a battery and this causes the fluid to deposit onto the cooling surfaces inside the radiator.

After the radiator change, the coolant temperature stays at just above 80 degrees C and when pulling up a steep grade might get to 85 degrees C.

Again, thanks for all of your help and hope that this solution will help other members.