Mariner speedometer pick up

[rich_k]

You've all done a great job in helping this newby understand how a boat speedometer works. Now if someone will assit me in finding the pickup on a 1994 40hp Mariner I think I can fix the problem. Looked on the leading edge of the lower unit but don't see any kind of hole or tube. My repair manual is no help either. Just get me to the pickup and I can handle it from there.
Thanks for all the help.
rich

 

[Texasmark]

Re: Mariner speedometer pick up

Not sure a 40 has an internal pickup. I know later model 90's and 150's do. If it has it the tube and pickup are obvious.

The way it works is water pressure working against a crescent shaped diaphragm that fills with water and air pressure trapped by the water. The higher the pressure the more the diaphragm attempts to straighten out hence moving the needle.

Mark

 

[rich_k]

Re: Mariner speedometer pick up

You've all done a great job in helping this newby understand how a boat speedometer works. Now if someone will assit me in finding the pickup on a 1994 40hp Mariner I think I can fix the problem. Looked on the leading edge of the lower unit but don't see any kind of hole or tube. My repair manual is no help either. Just get me to the pickup and I can handle it from there.
Thanks for all the help.
rich

Mark,
Wait a second I saw a cresent shape on the leading edge of lower unit. I thought it was a nick. Stand by I'll run out and stick a piece of weed eater line in it.
rich

 

[Texasmark]

Re: Mariner speedometer pick up

The crescent shape would be internal to the meter. Your speedometer is basically a pressure gauge and most pressure gauges work on this principle....like those party toys that are all curled up and when you blow into them they straighten out...type thing.

On the engine, you should have a small hole on the top front of the lower unit, just below the offset that is just below the antivent plate.....on mine anyway.

The hose exits right there above it (vertically), runs up the side of the engine and comes out alongside the wiring harness as a separate tube.

Mark

 

[rich_k]

Re: Mariner speedometer pick up

The crescent shape would be internal to the meter. Your speedometer is basically a pressure gauge and most pressure gauges work on this principle....like those party toys that are all curled up and when you blow into them they straighten out...type thing.

On the engine, you should have a small hole on the top front of the lower unit, just below the offset that is just below the antivent plate.....on mine anyway.

The hose exits right there above it (vertically), runs up the side of the engine and comes out alongside the wiring harness as a separate tube.

Mark

Mark,
I found it. I carefully ran a piece of weedeater line and some crud came out of the hole. I'll bet it was plugged. We'll find out when we get out next week if that was it. During the week I'll see if I can find any holes or worn areas on the tube. Thanks for the help!
rich