Alternator/Tachometer Issue Inboard Engine

[Joe18]

Hi Everybody,

Help/advice here would be greatly appreciated. When engine is started the Rev counter/Tachometer will read zero. Over a time span of 30 minutes it will gradually increase and eventually report a reading to the correct revs that the engine is producing. What do you think is the issue and what corrective correction do you recommend ?

Many Thanks for advice in advance

 

[VicS]

Hi Everybody,

Help/advice here would be greatly appreciated. When engine is started the Rev counter/Tachometer will read zero. Over a time span of 30 minutes it will gradually increase and eventually report a reading to the correct revs that the engine is producing. What do you think is the issue and what corrective correction do you recommend ?

Many Thanks for advice in advance

What engine? There are several ways in which rev-counters get their signal

From the ignition in the case of petrol engines, from a sensor "counting the teeth" on a gear wheel or from an output from the alternator in the case of diesel engines
By mechanical drive or a mechanically driven generator on very old engines

But my money would probably be on a defective tacho itself ... Have you checked the power supply to it and electrical connections to the sensor/ alternator etc

 

[jamie N]

Hi Joe, welcome to the forum. As Vic said of course, I'd start by checking every connector to the tacho by checking for corrosion, by looking at them, and making sure that each of them are metal to metal, not green to grunge.
Do you have a DVM for checking the wiring continuity, as it'll help as well.

 

[Joe18]

What engine? There are several ways in which rev-counters get their signal

From the ignition in the case of petrol engines, from a sensor "counting the teeth" on a gear wheel or from an output from the alternator in the case of diesel engines
By mechanical drive or a mechanically driven generator on very old engines

But my money would probably be on a defective tacho itself ... Have you checked the power supply to it and electrical connections to the sensor/ alternator etc

What engine? There are several ways in which rev-counters get their signal

From the ignition in the case of petrol engines, from a sensor "counting the teeth" on a gear wheel or from an output from the alternator in the case of diesel engines
By mechanical drive or a mechanically driven generator on very old engines

But my money would probably be on a defective tacho itself ... Have you checked the power supply to it and electrical connections to the sensor/ alternator etc

Hi Vic,
Thanks for advice, engine is an Inboard Mercruiser Diesel, alternator is powering two Batteries. Have checked the connections but nothing obvious. It’s a strange issue in that the tach will gradually increase from showing zero revs but steadily increase to full cruising revs, app 2700 pm. It is taking app 30 minutes to reach the correct reading.