how does this work

[deedubya]

I inherited a bayliner and put my own motor (with its own controls) on it. Everything on the boat works, except at the steering console where the speedometer and the fuel guage are. The speedometer feed is a flexible 1/4" tube from the back of the boat that seems to convey a water pressure, the fuel gauge just has a couple wires run from the inboard tank. Both display units seem to run through fuses (not blown). So before I just buy new units, I thought I might try to understand how each of these guys work, because it might be something stupid. So how do a fuel gauge and a speedometer actually work? and are there any thoughts on how to troubleshoot one? (The gas tank was real clean, so I wouldn't think a float would stuck. The water tube for the speedometer has great pressure at 30mph...

 

[Ross J]

Re: how does this work

The speedometer one I can answer. You're on the right track with the thought of pressure.<br />Water pressure bought about by moving forward in the water tries to force it's way up the tube thus creating pressure. This pressure works in one of two ways. <br />1 - it moves a diaphram, inside the speedometer, which causes the needle to show boat speed. - or<br />2 - it tries to straighten out a soft metal tube which is curved, which again moves the speedometer needle.<br />To be effective it needs three things - The pitot (I think I've spelt it right) tube needs to be in the water to get a pick up - the tube needs to be free of cracks or holes - the boat needs to be moving!<br />The only power you'd have comming to this unit would be for night lights. If it's not working and everything else is in order then a new one might be in order. I've never stripped one down before. Mine is 25 years old.<br />Ross

 

[deedubya]

Re: how does this work

Rossj<br /><br />Thanks much. Water pressure I've got. Tube was off before I knew what it was for and I thought we were going down. Just wasn's sure about the wires in the back of the unit. Got the gas gauge going this afternoon. Just needed a power hookup. Thanks again.