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Author Topic:   The 170 MONTAUK That Eats Tachometers
swist posted 09-04-2009 09:10 AM ET (US)   Profile for swist   Send Email to swist  
Two years ago the tachometer started reading erractically, mostly way high, on my 2004 170 Montauk with Mercury 90-HP FOURSTROKE engine with carburetors. Wiring seemed OK so I replaced the tachometer with a Teleflex Premier Pro unit on the advice of CW members. It is very close in appearance to the OEM tachometer.

All was fine for two years. Had to have been the tachometer itself, right?

Last week [the problems with the tachometer] started again. Exact same symptoms, jumps between correct reading and one considerably higher.

I am in a cold damp area of the coast of Maine, and this year has been really damp. When I pull the console cover off in the morning, all the gauges have a lot of condensation on the insides of the lenses, which usually burns off with the days heating. But needless to say, things are wet.

I'm wondering if these tachometers are simply not very robust in these environments, OEM as well as Teleflex. They are actually not very expensive in the scheme of things, particularly in the marine scheme of things. I use various kinds of electrical guages in my real job, and good ones are a LOT more than your typical $80 OEM marine tach.

Ideas? It's not that big a deal to keep replacing them, but maybe it's something else that someone has run into.

Tohsgib posted 09-04-2009 11:05 AM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Give it a shot of wd-40 every now & then?
weekendwarrior posted 09-04-2009 12:03 PM ET (US)     Profile for weekendwarrior  Send Email to weekendwarrior     
Get water tight gages. My Honda controls came with waterproof gages and a not-waterproof hour meter. The hour meter would get wet inside just like yours and it died at only 110 hours. 10 years later the waterproof gages are going strong. They should not get wet inside, look for waterproof replacements.
Tom W Clark posted 09-04-2009 12:09 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Check your voltage regulation.
swist posted 09-04-2009 12:23 PM ET (US)     Profile for swist  Send Email to swist     
If it wqas voltage regulation, I would think I would see the other gauges bounce at the same time - they don't. That also wouldn't explain why replacing the tach (at least the first time) fixed the problem (for two years).
rtk posted 09-04-2009 03:18 PM ET (US)     Profile for rtk  Send Email to rtk     
I have a problem with a Teleflex tachometer also. My engine is a 2003 Mercury 250 EFI. I installed one a few years ago and it did the same thing yours is doing in 2 months.

I also have the Smartcraft system on the boat to give me data. Charging voltage is dead on both batteries and the multiple tach readings I have through Smartcraft does not fluctuate a bit.

I'm not real happy with the quality of Teleflex tachometers. I had problems with another one on a different boat. I eliminated the charging system or ignition system as the cause of the problem. At 80 or 100 dollars a pop I expect alot more from a gauge designed to be on a boat.

By all means make sure your electrical system and ignition system is operating properly before buying a new one. But my experience has been that they do not hold up if they are exposed to the typical marine environment.

I don't define a typical marine evironment as garage storage.


swist posted 09-05-2009 07:19 AM ET (US)     Profile for swist  Send Email to swist     
All 4 gauges hasve about the same amount of condensation under the lenses after damp/cold weather. So the original Whaler gauges are not waterproof for all that money? Or is this the old "water-resistant" trick? Yeah they won't let water pour in, but they are open to the air (mainly in back) and will let humidity in?

an86carrera posted 09-05-2009 07:28 AM ET (US)     Profile for an86carrera  Send Email to an86carrera     
I am with Tom on this one. Mercury uses a signal from the voltage regulator for the tachometer.

Put an oscilloscope on the the tach signal wire.

Also, you could try switching the pulse switch on the back to another setting and then back to the original, it might clean up the contacts in there.


jimh posted 09-05-2009 09:03 AM ET (US)     Profile for jimh  Send Email to jimh     
The brand of boat, length of boat, or model of boat has likely nothing to do with this simple electrical problem. The tachometer calibration switch contacts are intermittent. This is likely caused by the marine environment, dampness, humidity, salt air, and poor design of the switch. To remedy this problem perform the following procedure:

--locate the calibration switch on the rear of the tachometer;

--note the current setting;

--operate the calibration switch throughout its range, moving it back and forth at least a dozen times using the proper tool, typically a very small blade screwdriver;

--return the calibration switch to the original setting.

swist posted 09-05-2009 01:11 PM ET (US)     Profile for swist  Send Email to swist     
This makes sense - will try next week.
swist posted 09-07-2009 09:05 AM ET (US)     Profile for swist  Send Email to swist     
Well Jim, you were approximately right on the money. Something is so corroded or otherwise shot inside the calibration switch that it no longer drops into the detents for the various pole configurations of different motors, it just turns smoothly like a pot. I know it just clicked into place when it was new. And after turning it back and forth several times, now there is no position that results in the tach reading anywhere near properly.

Time for a new one. I would get a waterproof gauge if it matched the Whaler OEM gauges, at least sort of.

swist posted 09-07-2009 09:08 AM ET (US)     Profile for swist  Send Email to swist     
It also strikes me that the fronts of the gauges are gasketed and the intrument panel has a sealant around the edges. This suggests the moisture comes in from the back - inside the console. I'm wondering if a little better ventilation into that space would help. As it comes from the factory, there is none.

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