Uh, no. With underdriven pulleys the accessories turn slower for a given RPM. If you slow the engine down, you also slow down the production of heat. It's the relationship between the engine speed and the water pump speed that's important.
Roger that. But, we switched to a 5.2" crank pulley and dropped the water pump speed by 15-20% and did not see any change in idle engine temps. (Using a Mildon high flow pump.) I just don't think a 10% underdrive is the likely issue in this case.
