Strangely, my car does the opposite, that is it runs too cool, regardless of the ambient temperature(which varied between 16-34 degrees C (that's 60-93 degrees F) this spring and summer).

The small plate in the engine bay gives the normal temp as between 60 and 80 degrees Celsius.

At highway speeds, the gauge stays at 60C or a bit higher, when slowing down it raises slowly towards 80C. After 5 hours of highway driving, when entered city, it raised to 80C and even one hair above.

Never checked the water temp with a thermometer to see if the sensor reads well, just trusted the "60-80C" recommendation.

The car doesn't have (and never had) auxiliary fan, just the main belt-driven fan. Coolant was standard antifreeze(unknown brand) + water, heavily diluted by adding more distilled water. Oil is 10W40, mineral (completed once with 1 liter of 10W40 semi-synthetic).

My uncle's 300E (from 1988, with A/C and single auxiliary fan) actually runs slightly warmer, around 85C. Paradox?

~Regards,

Nautilus

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1990 260E Sportline (that's 300E 2.6 for our American friends) -> sold
2001 E320 4Matic Elegance -> my Dad's daily drive
2005 Seat Leon FR 1.8T