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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have twin diesels (24v). Stb tach will run fine, then

Customer Question

I have twin diesels (24v). Stb tach will run fine for hours, then increase rpm (just the tach, not the eng) and swing 200-300 rpm for a short time, 10 to 30 minutes, then peg at 3000+.
I switched senders from Port to stb, but symptom stays on stb tach.
As a note, the part number indicates a 12v tach, but factory marked '24v' on back of instrument.
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.

Hi Art, my name is ***** ***** I will be helping you today.

Which model engines do you have?

You wrote that you swapped sending units between the engines. Have you tried swapping the tachs between engines as well?

Expert:  Jason replied 1 year ago.

It looks like you read my reply, are you still with me Art?

Customer: replied 1 year ago.
Jason, sorry about the delay. Slow internet at a previous marina did not allow me to interact; website just locked out. Now at different marina -website operating fine.
John Deere 6068TFM50 (new, have 250 hours, problem first surfaced at 60 hours or so).
Yes, I swapped tachs from right to left. problem stays with one tach. I don't believe it is related to power supply. Internal (lcd) hour meters work fine. Now both voltmeters also peg after some time of normal readings.
Expert:  Jason replied 1 year ago.

I don't work on those engines. I will opt out and leave this question open to the community. Good luck!