MPH gage not working

[prc03sx195]

What mechanism causes thois gage to read? I just changed the prop out and now it doesn't work, worked ok before?

While I am on the subject of gages, when I turn the power off the RPM gage does not go to zero, stays on about 500 rpm. Is there a way to fix this?

My boat is a 2003 glastron 4.3L I/O. Thanks

paul

 

[mrmushroomman]

Re: MPH gage not working

My rpm gauge does the same thing when i shut key off. When i turn key back on the gauge always drops to 0. As far as the speedo not woking, make sure the black hose towards the bottom of your outdrive is connected into the water pickup on outdrive for speedo. If the piece on the end of the hose is broke you can put another one on for a couple of bucks. I just replaced mine last week because it kept popping off.

 

[Knot Waiting]

Re: MPH gage not working

On the majority of boats the speedometer pick-up is a little white triangular mechanisim that hangs just below the hull on the boats transom. Usually has a hollow black tube comming up from it and entering the boat above the water line. Works by monitoring how much water is being forced into it to gauge speed. Usually stops working if it gets bumped by accident and doesnt sit at the correct angle.

 

[5150abf]

Re: MPH gage not working

As long as the tach zeros out when you turn the key on and works correctly when the engine is running it is fine.

It is probably a digital and they just do that, nothing you do to change it.

Your speedo is probably a pitot tube, at the back of the boat on the bottom should be a small tube in a casing, as the boat moves vacuum is applied to that tube, the faster you go the more vacuum, the more speed the gauge shows in theory.

You probably picked up something that is obstructing that tube.

I have never messed with one but I have read you can remove the tube from the back of the speedo and blow air through it to clear it until it clogs up again.

I would suggest a GPS unit, they never plug up and always work, even the cheapest ones are good anymore and you get the added advantage of mapping and being able to mark spots so you can find the again.

 

[marine4003]

Re: MPH gage not working

If you dont find the white pick-up mounted to the transom (rear) follow the black hose (3/16 dia) into the front of the outdrive,look where the zinc is attached to the front of drive above prop anti-cavatation plate,hose will come out of area where bellows hose is located and go into area at zinc.Look for unattached or torn - replace using splice

 

[Silvertip]

Re: MPH gage not working

Just to clarify, the speedo works on pressure -- not vacuum. Water pressure against the opening in the pitot compresses air in the tube that in turn tries to unwind a capilary tube in the speedo head. It is a closed system so water does not actually enter the tube very far.

 

[prc03sx195]

Re: MPH gage not working

Well I checked the rubber hose and all is well with it, not broken or split. I also blew some air into the hose and the speed needle moved a few MPH, so I guess the hose is ok.
So what else can I check? Can I get to the pitot tube easy enough or are they sealed? Please advise, thanks.

paul

 

[prc03sx195]

Re: MPH gage not working

Any one know of anything else I can check out before putting back in the water? What is connected to the fitting on the lower unit that the hose goes into? Does something rotate? Is it just by water going by a tube that causes air to be pulled in and sent to the gage? What else can go wrong? Thanks

paul

 

[Silvertip]

Re: MPH gage not working

The pitot is the white plastic pickup on the back of the boat. It has a tiny hole in it (facing forward) that gets clogged very easily. Clean it. If the tube is hooked to the pitot on the motor you have the same scenario. Clean it. There are only three parts to the system. Speedo head unit, the tube and the pitot. You've proven two of the three are ok. The pitot is plugged.