Quick Speedo Question (I think)

[DennisG01]

(info in signature) Does the speedo/pitot tube go all the way to the speedometer gauge in the dash? Or is there a sensor somewhere in between that converts the pressure to a digital form? IF there is a sensor, any idea on where it could be located? I do not see one inside the cowling area. Unless I missed it, I could not find a speed/pitot sensor listed in my service manual.

And... just to re-affirm myself... the pitot "hole" on the lower unit is the hole on the SIDE of the casing, correct? Meaning, it is not on the leading edge of the lower unit like I am used to seeing with Mercruisers?

[boscoe99]

In 99% of all Yamaha's the water/air pressure line goes to the back of the speedometer.

In about 1% of all Yamaha's the water/air pressure line goes to an electronic sensor. The sensor then conveys water pressure information to what Yamaha refers to as a Command Link speedometer. CL was introduced in the 2006 time frame for EFI four strokes and HPDI models only. The sensor is mounted on the block. The pressure line connects to it and then a branch of the engine's wire harness connects to the sensor.

The Pitot tube is located on the leading edge of the lower unit. Just like a Mercury Marine lower unit for an outboard or a stern drive. From the side it looks like a small scalloped area. Hard to see some times.

[DennisG01]

Cool, thank you. Definitely no sensor, then. (1) It's a 2000 and (2) the pitot tube comes up from the mid-casing area into the top case/cowling area and then connects to a barb fitting and goes into the rigging tube with the rest of the wires/cables into the boat. Pitot tube is definitely not connected to any sensor on the block.

Curious... what would that small hole on the side of the lower unit be? It's about the same distance above the gear case (torpeedo) as the "typical" pitot hole would be on one that is in the leading edge.

Just remembered something... I think the lower unit on this engine is from a 1997 model, if that makes a difference.

[boscoe99]

There are a number of holes on lower units so that water can drain and not freeze and damage the lower unit.

[DennisG01]

Well, what 'dya know! I must be a "one percenter"! Or, at least my engine is

I looked again at the trailing edge and there is no hole. The hole on the side of the lower unit that I referenced above has a "groove" leading to it - a lot like the water intake does. The groove goes from the hole towards the leading edge of the lower unit. I'm pretty sure that hole must be the pitot intake. I popped the hose apart at the barb connector that's inside the cowling and blew into the upstream hose (towards the dash) and the gauge reads perfectly.

So the issue is that the pitot hose is clogged somewhere. I used the drill bit method in the hole and then stuck a zip tie a good 8" up into the hole. No blockage. But, I can't blow bubbles in the water if I blow down the little hose that's inside the cowling (the downstream/pitot hole side of the barb). I then followed the pitot tube from the barb connector through the hole in the bottom cowling and towards the bracket. It's hard to see in there, but it appears that the hose might be pinched as it goes into that hole by the steering piece.

[99yam40]

I do not think any speedo comes from the side of lower unit.
Might look again

[DennisG01]

I do not think any speedo comes from the side of lower unit.
Might look again

That's exactly what I just did a few minutes ago. I was wrong and you guys are right. What I failed to mention was that I forgot to tell my brother, when he was antifouling the lower part of the lower unit, to avoid the pitot hole... which, at the time, I would have assumed was in the regular spot on the leading edge. When I looked for it there (trying to diagnose the problem), I didn't probe the anti-fouling hard enough and it was hiding under the paint.

I cleaned the paint off and reamed the hole with a drill bit for good measure - good as new!

I do wonder, though, why does that hole on the side of the lower unit have the groove in it? It looks as though it's there to help direct water into the hole?

Oh... I also forgot to tell my brother to avoid painting that lower, bracket-mounted anode...

[boscoe99]

Thanks for the feed back. Glad you found the hole.

Make sure that the paint was acceptable for use on aluminum. Should not have any copper in it. Copper and aluminum do not play nice together.

And don't forget the rule of holes. When you find yourself in one, stop digging.

[DennisG01]

Yup - used Hydrocoat Eco. I specifically picked that one so that I only needed one type of paint to use on the hull, bracket and motor. It's also safe to use over any existing paint.

"rule of holes"...