---AND
the opposite happens when the engine coasts. No work=less fuel burned, so engine temp always drops when coasting downhill.

Both of my 300's and my 6.9l Ford do this, it's just a Diesel thing.

Carried to an extreme, one time when towing our trailer across the Arizona desert near Wickenburg, the fuel filter loaded up so slowly that before long I had the accelerator floored on level ground and could only do 25 MPH.

On a gasser, the lean condition and heavy load would have driven the engine temp thru the roof-- but with the Diesel, the opposite happened. No fuel= low engine temp regardless of load. The temp gage was hugging the C side of the gage, barely off the stop. A new filter did the trick.

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Nate Stanley
(Currently Benzless)
1985 F-250 6.9l 170K
2009 SCION XB 36.5K
2003 LS430 78K
2012 Kubota B 2320