http://www.dieselsite.com/index.asp?PageAction=VIEWPROD&ProdID=186
Diesels run most efficiently at approximately 200o. A 195o thermostat will start to open at approximately 165o-170o. The Powerstroke has such an efficient cooling system, that this low flow when the thermostat is slightly open is normally enough to keep the engine cool. The downfall to this is that the engine -- when our trucks are not under load --never begins to reach its optimal operating temperature. Our 203o thermostat begins to open at 185o. This brings the operating temps up from about 170o to about 185o. This is closer to the operating temperature range that is preferable in our trucks for optimal efficiency.
When our trucks are under load and are producing higher combustion temperatures the 203o will allow the engine to run even closer to its optimal operating temperature. If the truck is under load and reaches the 203o setting, the thermostat is then fully open. This means you are at the maximum coolant temperature that the truck will reach. Your maximum temperatures are only a few degrees higher than in stock configuration, but these are degrees that you want for better performance. The best benefits come when the same truck is under a light load and would have a hard time reaching this optimal temperature. As stated above, you will never reach this optimum temperature with the stock 195o thermostat. The end result of installing the 203o thermostat should be slightly better fuel economy, less smoke, and maybe a few extra "ponies" to go along with it.
