Rpms Continually Read Low Dakota Tach Randomly Bounces Too Hight
| Author | Topic: Tachometer reading unexpectedly high rpm's |
| Frank O |  posted 09-03-2006 09:09 AM ET (US)  Yesterday on my 1995 21' Outrage with a 1994 Merc Offshore 225-hp 2-stroke outboard, a few minutes out of the harbor I noticed the (presumably OEM, analog) tachometer reading was unexpectedly high. It was showing 5,000-5,500 rpm, whereas the engine sound and boat speed were more consistent with something a little over 3,000. We cut the throttle, raised the engine to take a quick look at the prop, which appeared normal, then lowered the engine and resumed running. For the rest of the trip the tach remained in a more normal range. I know from my 32-year-old car (VW Karmann Ghia) that older instruments sometimes act up for a time, and sometimes mysteriously correct themselves. Left to my own devices, I'd probably keep an eye on the tach behavior, and maybe clip a portable tach to it in parallel for a second data point before taking further steps. Is there anything else I might check out? I noticed from searching older posts here that a non-working tach is often consistent with a bad rectifier in the charging circuit. Offhand the only thing I can think that would cause a tach to read high is if the instrument itself has a problem (or if I just ran across a spot in the ocean with a magnetic anomaly ...) |
| jimh | posted 09-08-2006 09:16 AM ET (US) If the tachometer has a calibration control on the rear of the instrument, observe the current setting. Then move the control back and forth across the range of settings, returning it to the original position. This may clean up a corroded or bad contact in the unit which is causing the calibration to jump to a improper setting. |
| Frank O | posted 09-11-2006 12:02 AM ET (US) Thanks for the suggestion, Jim. Today I went out to the boat to do maintenance on it, but didn't start the engine or take it out. Here's how the tach looked with the engine turned off and the boat sitting in the marina: http://www.inkbox.net/whaler/tach.jpg Hmmmm ... based on this, I suspected that tweaking the calibration might not help, but I checked it out anyway. Here's the tach's back: http://www.inkbox.net/whaler/tach-back.jpg I assume the black screwdiver-slot control at lower right is the setting for number of cylinders/pulses, while the light-colored control at top would be the calibration if anything. But playing with it didn't seem to help. Here are a few things I'm wondering now: 1) Does this tach look like original equipment for a 1995 Outrage? All the instruments were from the same manufacturer and had date codes on the back, and all were manufactured 1993-95. 2) Is it worth trying to find someone to try to repair a tach of this vintage? I've babied along speedometers for my car for several decades in the hands of great repair people. 3) If not, is a replacement tach of this style available now? I'd hate to throw off the look of the panel instruments by going to a different style of tach. |
| Frank O | posted 09-11-2006 12:03 AM ET (US) Thanks for the suggestion, Jim. Today I went out to the boat to do maintenance on it, but didn't start the engine or take it out. Here's how the tach looked with the engine turned off and the boat sitting in the marina: http://www.inkbox.net/whaler/tach.jpg Hmmmm ... based on this, I suspected that tweaking the calibration might not help, but I checked it out anyway. Here's the tach's back: http://www.inkbox.net/whaler/tach-back.jpg I assume the black screwdiver-slot control at lower right is the setting for number of cylinders/pulses, while the light-colored control at top would be the calibration if anything. But playing with it didn't seem to help. Here are a few things I'm wondering now: 1) Does this tach look like original equipment for a 1995 Outrage? All the instruments were from the same manufacturer and had date codes on the back, and all were manufactured 1993-95. 2) Is it worth trying to find someone to try to repair a tach of this vintage? I've babied along speedometers for my car for several decades in the hands of great repair people. 3) If not, is a replacement tach of this style available now? I'd hate to throw off the look of the panel instruments by going to a different style of tach. |
| rtk | posted 09-11-2006 01:17 PM ET (US) That is the same tachometer that was on my 1997 21 Outrage. I think the blue "Q" on the face of the gauge stands for Quicksilver, a Mercury parts designation. I replaced mine this season, it was acting up the past two seasons. I replaced all the gauges so I did not attempt to find a match. A Mercury dealer may be able to find a similar tachometer that will match that one. I don't think these gauges are designed to be repaired, so a new one is your only option. Rich |
| Frank O | posted 09-11-2006 01:52 PM ET (US) Thanks, Rich, I'll check that out. When you replaced all your gauges did you get them from the same mfr./style so that they all match? If so, what did you go with? |
| jimh | posted 09-11-2006 08:06 PM ET (US) It is absolutely normal that a tachometer dial indicator not return to the zero mark when the motor is off. This is not an indication of a problem. If you did not run the motor you don't have any idea if you fixed the problem or not. Move the calibration control back and forth a few times, returning it to its original position. Start the motor. See if the reading on the tachometer is more accurate. |
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