Speedometer block pressure system.

[jerryjerry05]

This is a "new to me" motor.
​2002 225 EFI OT555086
The speedometer bock pressure system??
What does it do? The hose from the lower to the motor is cut or broken?

THANKS!!

 

[Silvertip]

It is not a back pressure system. It is a pressure system. The hose runs from the back of the speedometer to the pickup built into the lower unit of the motor. As the boat moves forward water pressure compresses air in the tube and the speedometer indicates related speed. So the speedo is like a pressure gauge, just calibrated in MPH/KPH. No water actually flows through the tube (unless it is cut).

 

[jerryjerry05]

It should have said BLOCK not bock pressure
​So it's just like the pitot tube on the boat.
​Thanks,