Tach and speedometer problems

cmassa

New Member
Jul 11, 2010
55
Northern California
Boat Info
2005 Sea Ray 185 Sport
Engines
4.3L Mercruiser, Alpha outdrive
I've been having problems with my speedometer and tach this season in my 2005 185 with 4.3 engine. The speedometer reads 12-15 mph slow and frequently doesn't even start to register until at 18-20 mph. I've blown out the tube from the gauge end and there does not appear to be any obstruction anywhere in the line, including at the drive unit. I've been using my iPhone as a speedometer which has worked well but would like the gauge to work properly (also I'm scared I'll drop it in the lake!) I've searched the forums but couldn't find info on where to go from here.

The other problem is the tach. It will vary between 3,000 and 4,000 when cruising with no change in speed, throttle, or engine sound, usually reading quite high for our current speed. Eventually it settles down but will still occasionally jump up. Connections are tight on the back of the gauge. I don't know where the engine end is to check that but haven't found any loose connections.

Any recommendations?

Thanks.
 
First guess on the speedo is a bad hose. Since the speedo works on pressure it sounds like you're not getting a good seal. Do you have a way to test it's integrity? Of course the speedo itself could be bad also.
Tachs are notorious for bad connections. On most tachs there is a small switch to go from 4, 6, or 8 cylinder. Usually using a small screwdriver, cycle through the range 20 times and set it back on the proper setting. Good luck!
 
For the tach, exercise the switch that is on the back side of the tach. Make sure it ends up on the "6C" position. That would be the best place to start.

For the speedo - if you physically cleared/checked the tube, including disconnecting at the QD fitting above the ventilation plate and using some compressed air (or other way) to verify air flow... I would wonder if you have a split/crack in the tube, or if it isn't seated well on the nipple where it goes through the transom plate. Fashion an air hose to the pitot hole in the drive so you can apply a few pounds of air to pressurize the hose without any escaping. Listen for air leaking somewhere.

Another possibility is that the hose is creased somewhere along it's run. That, you'll just have to follow it from the speedo to check.

EDIT: Wow - it took me an extra 9 minutes to type that, compared to Dick!
 
I moved the switch a few times and the tach worked fine yesterday.

I think I may have narrowed down the problems with the speedometer. I think it is the connector on the drive where the tube starts. I took it off again and seated it down again. It worked much better for about 3-4 minutes but then stopped again. Probably not getting a good seal? I can't tell if there is an o-ring in there, damaged or missing? Anybody know a good place to buy another connector? There are no parts shops where I live. While I'm at it I may just run a whole new tube rather than try to inspect the old one. It dives into a conduit just after the gauge and is not visible. Is it a special type of tubing? Sure looks like 1/4" irrigation drip tubing (but I haven't actually measured it).
 
EDIT: Wow - it took me an extra 9 minutes to type that, compared to Dick![/QUOTE]

I took typing in high school (class of 72) because I was the only guy in class plus the teacher was a knockout! Never dreamed I would actually use the skill. Started using a computer at work in 1973 (the only one with typing skills) and have been on one ever since. I'm old, not necessarily slow!
 

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