What battery size?

[Dave]

I have a Yanmar 27hp (3GM30F). What is the recommended battery size either in marine cranking amps (MCA) or cold cranking amps (CCA)? I have a new battery that claims to have 650 MCA. It barely turns the engine over. Once in a while, after a sluggish turn or two, the engine will start. When I connect the second battery, it starts right up. When I leave shore power connected, it start right up. I spent the weekend with a voltmeter checking everything from cables to switches. It really appears that it just needs more amps to turn over easily. Unfortunately, I do not know what the original battery was rated so I don't have that for a comparison (long story).Thanks

 

[Derek Rowell]

I suspect the starter motor.

I had exactly the same problem with the 22hp Yanmar on my old H34. Would hardly start on one Group 27 battery, even when the battery was brand new. After I sold the boat, the new owner replaced the starter motor, and that solved the problem!

 

[Don Berger]

Bad connection?

It sounds like a bad connection. You said that yopu checked them all but if you didn't check voltage while cranking, a bad connection would likely not show up between the battery, solenoid, starter switch and starter. Some corrosion albeit invisible, may not manifest itself under no-load conditions. I'd bet that removing all the cables and cleaning everything would be time well spent before adding a second battery which NO engine should need to start.Don

 

[Gord May]

Check the Negative

ground connection. The starter & solenoid use a bolted connection to engine - not a discrete cabled negative. Check the bolt-block interface. Tight, clean, etc.

 

[Bill]

Jumper Cables

Try using jumper cables to by pass some questional areas ie. the negative wire from the batt to the motor, then the positive. If you have a wire or connection which is going bad, a volt meter won't necessarly pick it up, yet the proper amount of cranking amps can't get thru.

 

[Paul]

Probably OK

I have the same issue with my 3GM30F. One battery will turn the engine if it is at a near complete charge, but it labors. If I switch in battery #2, even if it is 50% discharged, the engine spins like a top.650 MCA is actually a little shy for a diesel starting battery. It's common to see 800 CCA for a dedicated starter. There's a lot of compression to overcome.Maybe your conclusion is correct: you just need a few more amps.I like the jumper cable idea! I'd try that just to confirm your conclusion.Paulsv Escape Artisth336