Speedometer question

[iggyw1]

I have a speedometer on my boat that has some type of nylon pick up unit at the bottom of the transom. From this nylon fixture, it looks like it is just a hallow tube going thru the upper part of the stern and to the speedometer in the dash board. The speed ometer quit working for me the other day, and today it was working sometimes and sometimes not working. can someone explain where I should start to troubleshoot this problem? I don't even know how the thing works at all with just a hallow tube. Thanks!

 

[kjsAZ]

the speedo "measures" the pressure generated by the water pushing onto this little plastic tube called a pitot tube. It operates like a barometer and shows the air pressure in that hose as speed. Most likely the pitot tube is clogged with some debris. The hose if kinked or has a hole will also prevent it from working.

You can disconnect the hose from the pitot tube and blow into it (hard) and have someone watch the gauge. If it works then you know that that pitot tube needs some cleaning.

 

[Bubbasboat]

Pull the tube off pitot and blow thru pitot, if that's clear, remove tube from back of speedometer and blow thru tube from speedometer end. As kjsAZ said, likely your pitot has gotten clogged. Had similar issue this spring.

 

[iggyw1]

Thanks guys! I can see why I should blow from the gauge end of the tube as to not blow any clog inside of the tube up higher into the tube or even into the gauge itself. I will also remove it from the end at the bottom of the transom and blow on the nylon thingy (pitot?) to make sure that is clear too. Thanks again!