Mike,
the thermo/wax valve is adjustable. There is an Allen plug on the end that you can remove, once removed, there is another Allen that can be turned CCW to slow fan down if my memory is correct. By turning it CW, it restricts flow, turning fan motor faster. A quarter or half turn is all you need to make the fan speed up or down. Do not run engine with outer plug removed. Make your adjustments, then replace outer plug before starting motor. Hope this helps.