Troubleshoot speedometer problem

[hkeiner]

I generally understand that a speedometer gauge works by measuring the air pressure in a tube coming from the pickup located in the lower unit of my motor. I also understand that the pickup and tube have to be clear and unplugged for the gauge to work. I also understand that the water pressure at the pickup causes the air in the tube to compress which the gauge at the dash then measures.​

I don't understand, however, how far the water normally moves though the tube (from the pickup towards the gauge) when everything is properly connected and whether it would flow through the tube if I were to disconnect the tube at the gauge and then drive the boat. I would like to know this for troubleshooting purposes. I figure that by monitoring the water flow rate in the hose before and after I poke, prod, clean, or replace the pickup and hose, I can tell if it is doing any good.​

The speedometer on my boat does not work most of the time. It does randomly show the accurate speed for a few minutes at a time, but mostly it justs displays 0 MPH. I was thinking of disconnecting the tube from the back of the gauge and then monitoring the flow of water coming through the tube while the boat is moving at varying speeds. I presume that if the hose is disconnected, then the air could escape and thus allow the water to flow through the hose. This would not work, however, if there is some type of membrane in the pickup preventing the water from flowing into the hose.​

Thanks for any infomation on this.​

 

[tashasdaddy]

Re: Troubleshoot speedometer problem

it sound like you have a clogged tube or pickup. disconnect at the dash and blow compressed air thru it. insects love to make homes in the little tubes and crevaces. oncew cleared you can blow compressed air into pitot, and see if the guage works, actually you could take short piece of tube connect to the speedo and pressurize it. becarefully don't blow out the speedo if it does happen to work.

 

[hkeiner]

Re: Troubleshoot speedometer problem

it sound like you have a clogged tube or pickup. disconnect at the dash and blow compressed air thru it. insects love to make homes in the little tubes and crevaces. oncew cleared you can blow compressed air into pitot, and see if the guage works, actually you could take short piece of tube connect to the speedo and pressurize it. becarefully don't blow out the speedo if it does happen to work.

Approximately how much PSI pressure is apporpriate without damaging the gauge, hose, or pitot? I don't have a compresser but I do have a bicycle pump with a built in pressure guage, which I can probably jury rig to work.​

Any information on my earlier question regarding expected water flow through the tube with the tube connected or disconnected from the gauge?​

Thanks​

 

[tashasdaddy]

Re: Troubleshoot speedometer problem

never tried it, but with nothing to stop the flow, if running wot, the little hose would throw a pretty good stream. like a fire hose. that's my guess. would be pretty neat to see. like you yamaha wave runners stream.

 

[fishing4fun24]

Re: Troubleshoot speedometer problem

Hi everyone!!! Boy I sure hope someone can answer this. I understand how a pressure speedometer works I think. My speedometer has never worked. the plastic piece on the back is clear of deburie same as the hose still dont work. O well but my question is to help me trouble shoot it is this. If the gauge is run on pressure how come in back of the speedometer it self has wires going to it. Seems to me that they would not be needed if it is only run on pressure. Anyway I really hope someone will help me. It would so be so much appriciated. Thanks guys..

 

[hkeiner]

Re: Troubleshoot speedometer problem

The speedometer works using the air pressure in the black hollow tube that connects to the back of the gauge. The wires your see are to light up the gauge at night when the dash light switch is turned on.

 

[fishing4fun24]

Re: Troubleshoot speedometer problem

O no Kidden. Well i blew out the black tube and it's going to get wet for the first of the year. I will let you know how it goes thanks.