Speedometer not consistently working

[Dave87]

Hi everyone,

Thank you for all your help.

My speedometer doesnt always work and I was wondering what the solution was to fix this.

Do I need to buy a new gauge ? Or is it something else.

Thanks

 

[wellcraft-classic210]

Can you tell us what year and outdrive // If its an alpha its driven by vacuum


Alpha 1 Gen2's were more accurate and built into the drive // Gen 1's typically had a an added sensor on the transom

In either case they are vacuum driven / and any leaks will affect readings // I would inspect the tubing connections first -- If the line has enough slack cutting off the last inch that may be stretched out and sealing with a fresh section of hose may help. A vac pump tool for autos can help debug this as well.


The GPS's these days are much more accurate for mph than the vac sensors.

 

[Dave87]

Can you tell us what year and outdrive // If its an alpha its driven by vacuum


Alpha 1 Gen2's were more accurate and built into the drive // Gen 1's typically had a an added sensor on the transom

In either case they are vacuum driven / and any leaks will affect readings // I would inspect the tubing connections first -- If the line has enough slack cutting off the last inch that may be stretched out and sealing with a fresh section of hose may help. A vac pump tool for autos can help debug this as well.


The GPS's these days are much more accurate for mph than the vac sensors.

It is a 1991 mercuiser I/O Alpha One

So all my problems would be coming from the tube at the bottom of the foot and not the spedometer itself ?

 

[Scott Danforth]

its actually pressure driven.

its called a pitot tube speedometer

the alphas simply had the passage internal vs an external pitot tube pickup

easy to check. if you cant blow thru the tube, its plugged.

test the gauge using air pressure: 5.6 PSI = 20 MPH; 12.6 PSI = 30 MPH; 22.4 PSI = 40 MPH; and 35 PSI = 50 MPH.

 

[wellcraft-classic210]

Scott

Thanks for clarifying the pressures