True, true... I knew I'd probably get that response at some point, and deservedly-so. I mostly feel the same way, but I've got a pretty bad case of OCD, so knowing what "ideal" is and seeing that I'm not there really drives me nuts! And knowing that it's better for diesels to be a little too warm rather than a little too cold is a good thing still doesn't help, unfortunately.

In my experience, German cars' temperature gauges (like VW and MB) are much more sensitive than their American and Japanese counterparts. They actually go up and down as the engine temperature does! The only times I've ever seen in an American temperature gauge do anything other than stay at the dead-center middle is during warm-up and overheating! My '81 VW Rabbit Pickup always ran one-and-a-half notches hotter than center (similar to what is happening in my 300SD) and it drove me nuts in that car too! Perhaps American-made vehicle owners are happiest with the "ignorance is bliss" approach. The Fords, Mazdas, and GMs I've owned always stay right in the middle of the temperature gauge. I never worried about temperature in those vehicles. Has anyone else noticed anything along those same lines?

I've only owned the 300SD since last September, and I figured that the very cold temperatures we had here last winter were the main reason I hadn't overheated. Now that the weather is getting warmer and the hot summer is on its way, I wanted to address this "issue" before it gets too hot here.

The last thing I'm considering trying is a Shout/citric acid flush. I'm not sure of the condition of the inside of the engine block's coolant pathways, but as I mentioned before, the coolant from my original flush was very clean. What I forgot to mention is that that same coolant was green. I don't know if it was conventional green or an extended-life green. Either way, it wasn't the Zerex/MB coolant it should have been, and I don't know how long it was driven that way.

Is the Shout/citric acid flush very effective? Has anyone seen measurable results from such a flush?

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1984 300SD
351,000 miles

If it is any consolation, I have the exact same vehicle and it, too, runs close to 100C. whenever it feels like it. I, too, have replaced everything but the sending unit. Nothing affects the result.

My infrared thermometer does show a slight benefit............93C. on #6 when the gauge shows 100C.

I'm tired of worrying about it..........the engine doesn't care if it runs warm (actually preferable for fuel economy).........why should I?

With a 50-50 mix of Xerex and a pressure of 15 psi, the boiling point is 128C. and the engine can run safely right to 120C. without any issues.