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Discussion Starter · #1 ·
I've been mucking around with overheating issues for some time and finally solved the problem by removing and cleaning the mixing elbow. During that time I also replaced my water temp alarm with a new sending unit and guage. For some reason now my tachometer doesn't work and I have no idea why. How does the rpm get measured on a diesel since there is no distributor or ignition box? I do have one loose wire hanging near the engine but think I remember that to have been connected to the alarm sending unit. Any thoughts??
 

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Do you have an ammeter or a battery monitor? Tachs on diesels are either run off the alternator or a pickup off the flywheel, usually a single wire sensor bolted into the bell housing/adapter. If the tach is off the alternator and it quits that's usually brushes (or a dropped wire) but if it's brushes then you won't be charging either.

Your loose wire is the first place to look.
 
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Discussion Starter · #3 ·
Thanks Faster! During my cooling issue problem I started at the saltwater seacock and checked the flow all the way through the system to the mixing elbow. I also found that the sea water strainer unit was old and corroded enough that it was going to cause me grief sooner or later and so replaced it with a new one. It's likely that in that cramped and dark working area I may have snagged a wire at the bellhousing. I'll check that area out next weekend as I doubt my unidentified loose wire will reach the alternator.
 

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Tspooner

On our boat the tach is energized when oil pressure detected by the oil pressure alarm sensor. Check the loose wire may have been connected to one of the oil pressure senders. Sea Dragon, Westerbeke W40, has two oil pressure senders. One which closes an electric circuit when oil pressure is sensed (this is a way of identifying whether the engine is running or not – this is used to activate the hour meter which is part of our tach along with other "things") the other reads oil pressure for the oil pressure meter.

This may or may not help.

Good Luck,
Garner
 

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Discussion Starter · #5 ·
That loose wire is in proximity to both temperature and oil sending units. I'll also check to see if the hour meter has turned over since our last outing on Saturday as I always record the hours in the log book prior to starting the engine to exit the marina.
 

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T,

Can you come back and post the results when done, this would be of great help to others with similar issues.
I'm pretty sure it's just a loose wire :)
 

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Discussion Starter · #8 ·
Unfortunately my checks and actions over the weekend didn't produce any positive results. My "extra" loose wire is the original temperature wire from the old sending unit. It wouldn't reach the oil pressure unit or the alternator and reattaching it to the new unit didn't change a thing. All the wires on the alternator are protected by a boot and all were intact. Nothing appeared amiss at the bellhousing/clutch neither so I'm back to square one. I'll recheck the wiring at the tach itself behind the ignition/start plate next time out although it all seemed fine when I first looked.
 

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T... Don't think you ever confirmed whether or not you were actually charging?
 

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My boat came with a blown alternator, and then I blew the diodes on the replacement by turning off at the key before stopping the engine. In both cases, the tachometer would not work. As Faster says, you really need to check that you have a healthy charging voltage - 14V or more.

If not, either the alternator is faulty, or it is not getting the excite voltage via the ignition switch.
 

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My boat came with a blown alternator, and then I blew the diodes on the replacement by turning off at the key before stopping the engine. In both cases, the tachometer would not work. As Faster says, you really need to check that you have a healthy charging voltage - 14V or more.

If not, either the alternator is faulty, or it is not getting the excite voltage via the ignition switch.

Mark,

I would love to know exactly how that alternator was wired so that turning off the key disconnected it from the load? Turning off the key has zero effect on most alternators. The only time it would, could be if a PO improperly wired something... Most factory alts are either key on excite or self sensed. With key on excite turning the ignition key off just turns off the regulator and the alt shuts down. With self sense excite it keeps on working even with the key off and unless the key also turned off the battery switch or other funky home brew configuration then the alts keeps running.
 

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The boat was wired with excite via the ignition key. So yes, I just disconnected the excite. Some alternator expert told me that disconnecting the excite while an alternator is putting out a good output is not good practice. Most of the time, it might be OK, but occasionally, not so. I think generally most of us avoid bad practice on principle.
 

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Discussion Starter · #13 ·
T... Don't think you ever confirmed whether or not you were actually charging?
No, that was one step I missed due to a misplaced multimeter which I have now replaced with a new one. I'll be back up there for the Saturday race (brrr) and will check that out as well though there seems to be plenty of battery for starting the engine.
 

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Could you possibly reverse the original fix (replaced sender, etc.) and see if the tach problem still exists? If not, your answer could be in the incompatible or defective replacement parts.
 

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If you have a "one wire" alternator, where the sense lead is tied back to the output (usually at the starter lead) then you may also have to blip the engine to get the alternator to turn on, and the tach won't read until then. Blip can mean 2x-3x cruising speed for 5-10 seconds.
 
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