I used to run a 160degree thermostat in my 351W and it always indicated in the 170s. Either Vince or Rich at skidim had me install a 145degree thermostat and now the gauge sits right on 160, which is where the manual says to run it.
Yours being a 2008 is probably different, but the point being that you motor may not Necessarily operate at the temperature marked on your thermostat. A lot of guys I know don't even use one, but mine really needs it because she don't like to run cold.

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