Webster Hydraulic Fan Motor

[davidbrady]

Incidentally Tommy, the Webster Pressure Relief Valve is one of the reasons that 8V92's get slightly poorer fuel mileage than the other birds. A while back Leroy and DonB reported that their 8V's got the same mileage regardless of the fan override being on or off; whereas, my S60 get's 0.5 mpg difference under these scenarios. The difference is that on the S60 when the fan is off pressure is relieved in the hydraulic system; that is, no work is done and the pump simply freewheels. The Webster Pressure Relief valve always maintains pressure in the 8V systems whether the fan is on or off, or whether the power steering is calling for pressure or not. IOW's the pressure relief valve only dumps pressure in excess of some amount, say 3500 psi. It needs to do this because the system is shared by both the fan and the power steering. The relief valve pressurizes the system by default so the power steering can work. All this adds up to work being done even though neither the fan nor the power steering is using it. The result: a constant fuel mileage hit!