There are a number of 4th cylinder cooling options what are you thoughts.
1)Water pump to 4th cylinder before and after impeller- I think before impeller may be best of the two.
2)4th cylinder to thermostat waterbox - due to low pressure differential I seriously doubt the this is any more than a trickle
3) 4th cylinder to heater core/bypass - I feel this is likely the best for cooling #4 but I hear that this causes limited flow at the coolant sensor