My two 617.652 engines have completely different temperments (no pun intended..) so, you may simply need a flush and fill. Or, it may just be the way things are.

For reference, my TD runs 'cool' almost all of the time, with the A/C on and at highway speeds, the needle is at the top of the eight in the 80°C marking. Extended idling in the afternoon Texas sun will run her halfway up to the 'no number' mark at 100°C.

Under the same conditions, SWMBOs 300D almost always runs at a point just about 2-3 needle widths below the 'no number' mark and will creep up close to the mark after lengthy idling. Instructions to SWMBO is that if the needle goes above the 'no number' mark, shut her down immediately and call for assistance.

Later this fall, I plan to flush the systems with MBZ citric flush and replace all hoses. MBZ coolant will go back in when I'm done.

I'll be interested to see what they both do after that service.

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Never a dull moment at Berry Hill Farm.