Just started doing the same, using Scan Gauge II. Lost the water pump last November on the road and wasn't able to know until it went into limp mode. Why they don't have a temp gauge is silly. Water temp range once driving ~100C - 105C. More important, also I'll be monitoring the Trans fluid temp as I occasionally tow a horse trailer.

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Bob Voskian

2012 BMW X5 3.5i
2014 BMW 535i xDrive (wife's)
1991 Porsche 928 GT 5 speed (44K miles)
2003 MB SL 500 (wife's summer car)
2004 Audi TT 3.2 quattro with DSG