Faulty Magnetic Switch on 3GM30 Starter

Roy M · 31-05-2009, 17:33

My engine wouldn't start. I had tons of power available, good wiring, but no activity at all from the starter. I traced voltages all the way to the starter, no problem there. I pulled the starter off, scratched my head, and read the service manual. The continuity tester buzzed when I touched the case and the Start cable terminal, what Yanmar calls the Shunt coil continuity test. It means I have to replace the switch. Is this the same thing as the solenoid switch? I tapped on it with a small hammer (doesn't everyone?) to effect some magic cure, but no dice. The engine isn't more than 100 hours old. Is this unusual? What might have caused such a failure?

Chief Engineer · 31-05-2009, 18:23

Did you try jumping the starter?

senormechanico · 31-05-2009, 20:58

If it's like a 3HM35F, there is a multi wire plug near the back end of the engine which goes to the gauge console. The split pins get relaxed and make poor connections. Spread them slightly SLIGHTLY! and give them a bath with WD 40 or similar. Plug back together and you will probably solve it. Mine stayed fixed for years after that, and was still going strong when I sold the boat.

Steve B.

Roy M · 01-06-2009, 08:27

Hi folks, I like both your suggestions. However, when I removed the starter and magnetic switch assembly, then tested the continuity between the S terminal and the body of the magnetic switch, I learned there is continuity, hence, according to the Yanmar service manual, that the coil is open and that the switch, itself, not the whole starter, must be replaced. My question is why, with a motor this young (under 100 hours), would the coil short out to the case? All of the wiring and engine parts are clean, dry, and well painted, with no evidence of moisture or heat damage. I'm trying to understand the pathology of this failure. I'll probably pick up a new magnetic switch, after confirming with the parts store, that this test is accurate. I will also open the engine harness plug assembly and perform the suggested adjustment and moisture dispersal.

Cheechako · 01-06-2009, 08:42

Failures do happen with new things. My Yanmar 3GM30 had to be completely replaced at 500 hours!

Southern Star · 01-06-2009, 09:49

Roy, I'm not sure about a continuity test (nor of what 'switch' they are referring to), but I can say that Yanmar 3 GM30's are notorious for substandard wiring from the control panel/ignition switches to the starter motor. One of mine had a sporadic starting problem which seemed to vary with the position of the throttletransmission lever. I had assumed it was the neutral contact switch, but even when bypassed, the problem was not rectified.

I then replaced the solenoid - same result. It turns out that by replacing the wiring harness with heavier gauge, tinned wire I was able to correct the problem; the variance with the position of the throttle/gear lever was because the wires had been attached to the cables and the slight movement of the same would sporadically correct the short. In any case, I am led to believe that this is a common occurence with the 3 GM30. The good news is that you do not have to pay (and should not) the exorbitant price charged for a replacement harness as they will have the same inadequate wires. There are not that many wires that relate to the ignition, so simply run new lengths of tinned wire of a slightly heavier gauge (as I recall, I used #10). Take note, prior to the repair, mine was still showing current at the solenoid when the starter button was engaged; it was, however, insufficient to engage the solenoid until I installed new wires.

Brad

ggray · 01-06-2009, 20:26

For extra long wiring runs (can't remember how long that is) from the panel to the engine, Yanmar has available a relay that energises the starter solenoid (is this what is being referred to as a magnetic switch ?) So you have one relay energising a second relay. I assume this would be more effective on long runs than running a heavier wire.

I installed these optional relays on the engines of our catamaran because I had heard of starter problems on these boats presumably from the long runs we have.

Last month, at 9 years of age, one engine had trouble re-starting when it was hot. After checking all connections in the starter cables, I had the starter tested. Was deemed faulty, so was completely rebuilt.

However, last week, that engine failed to crank one time when it was hot, so I'm not sure I don't have another problem. I'll look for this plug connector on the engine to see if that needs attention.

Roy M · 01-06-2009, 21:05

This is quite interesting regarding the harness wiring. Again, I had made an assumption that it would be adequate, but reality raises its cruel head yet again. The panel is quite close to the engine, but, as you point out, the harness is what it is, so a modification may be in the works. I love this forum. Thank you, gentlemen, for your participation, advice, and reassurance.

Chief Engineer · 01-06-2009, 21:14

Not cranking when the engine is hot is usually a sign of a bad starter solenoid.

If the windings in the solenoid are hot...the resistance goes up.

Have you tried to jump the starter yet?

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31-05-2009, 17:33	#1
Roy M Registered User Join Date: Feb 2007 Location: Southwestern Yacht Club, San Diego, CA Boat: Searunner 40 trimaran, WILDERNESS Posts: 827 Images: 4	Faulty Magnetic Switch on 3GM30 Starter My engine wouldn't start. I had tons of power available, good wiring, but no activity at all from the starter. I traced voltages all the way to the starter, no problem there. I pulled the starter off, scratched my head, and read the service manual. The continuity tester buzzed when I touched the case and the Start cable terminal, what Yanmar calls the Shunt coil continuity test. It means I have to replace the switch. Is this the same thing as the solenoid switch? I tapped on it with a small hammer (doesn't everyone?) to effect some magic cure, but no dice. The engine isn't more than 100 hours old. Is this unusual? What might have caused such a failure?

31-05-2009, 18:23	#2
Chief Engineer Commercial Vendor Join Date: Aug 2006 Location: North of Baltimore Boat: Ericson 27 & 18' Herrmann Catboat Posts: 2,444	Did you try jumping the starter?

31-05-2009, 20:58	#3
senormechanico Registered User Join Date: Aug 2003 Location: Whidbey Island WA Boat: Dragonfly 1000 trimaran Posts: 1,374	If it's like a 3HM35F, there is a multi wire plug near the back end of the engine which goes to the gauge console. The split pins get relaxed and make poor connections. Spread them slightly SLIGHTLY! and give them a bath with WD 40 or similar. Plug back together and you will probably solve it. Mine stayed fixed for years after that, and was still going strong when I sold the boat. Steve B.

01-06-2009, 08:27	#4
Roy M Registered User Join Date: Feb 2007 Location: Southwestern Yacht Club, San Diego, CA Boat: Searunner 40 trimaran, WILDERNESS Posts: 827 Images: 4	Hi folks, I like both your suggestions. However, when I removed the starter and magnetic switch assembly, then tested the continuity between the S terminal and the body of the magnetic switch, I learned there is continuity, hence, according to the Yanmar service manual, that the coil is open and that the switch, itself, not the whole starter, must be replaced. My question is why, with a motor this young (under 100 hours), would the coil short out to the case? All of the wiring and engine parts are clean, dry, and well painted, with no evidence of moisture or heat damage. I'm trying to understand the pathology of this failure. I'll probably pick up a new magnetic switch, after confirming with the parts store, that this test is accurate. I will also open the engine harness plug assembly and perform the suggested adjustment and moisture dispersal.

01-06-2009, 08:42	#5
Cheechako Registered User Join Date: Aug 2006 Location: Skagit City, WA Boat: Fellippi 32 Posts: 2,371	Failures do happen with new things. My Yanmar 3GM30 had to be completely replaced at 500 hours!

01-06-2009, 09:49	#6
Southern Star CF Adviser Join Date: Dec 2007 Location: Belleville, Ontario, Canada; Playa Zaragoza, Isla de Margarita Boat: 1994 Solaris Sunstream 40 'Estrella del Sur' Posts: 1,071	Roy, I'm not sure about a continuity test (nor of what 'switch' they are referring to), but I can say that Yanmar 3 GM30's are notorious for substandard wiring from the control panel/ignition switches to the starter motor. One of mine had a sporadic starting problem which seemed to vary with the position of the throttletransmission lever. I had assumed it was the neutral contact switch, but even when bypassed, the problem was not rectified. I then replaced the solenoid - same result. It turns out that by replacing the wiring harness with heavier gauge, tinned wire I was able to correct the problem; the variance with the position of the throttle/gear lever was because the wires had been attached to the cables and the slight movement of the same would sporadically correct the short. In any case, I am led to believe that this is a common occurence with the 3 GM30. The good news is that you do not have to pay (and should not) the exorbitant price charged for a replacement harness as they will have the same inadequate wires. There are not that many wires that relate to the ignition, so simply run new lengths of tinned wire of a slightly heavier gauge (as I recall, I used #10). Take note, prior to the repair, mine was still showing current at the solenoid when the starter button was engaged; it was, however, insufficient to engage the solenoid until I installed new wires. Brad

01-06-2009, 20:26	#7
ggray Registered User Join Date: Mar 2009 Location: Southern Chesapeake Bay Boat: Norseman 430, Jabberwock Posts: 102	For extra long wiring runs (can't remember how long that is) from the panel to the engine, Yanmar has available a relay that energises the starter solenoid (is this what is being referred to as a magnetic switch ?) So you have one relay energising a second relay. I assume this would be more effective on long runs than running a heavier wire. I installed these optional relays on the engines of our catamaran because I had heard of starter problems on these boats presumably from the long runs we have. Last month, at 9 years of age, one engine had trouble re-starting when it was hot. After checking all connections in the starter cables, I had the starter tested. Was deemed faulty, so was completely rebuilt. However, last week, that engine failed to crank one time when it was hot, so I'm not sure I don't have another problem. I'll look for this plug connector on the engine to see if that needs attention.

01-06-2009, 21:05	#8
Roy M Registered User Join Date: Feb 2007 Location: Southwestern Yacht Club, San Diego, CA Boat: Searunner 40 trimaran, WILDERNESS Posts: 827 Images: 4	This is quite interesting regarding the harness wiring. Again, I had made an assumption that it would be adequate, but reality raises its cruel head yet again. The panel is quite close to the engine, but, as you point out, the harness is what it is, so a modification may be in the works. I love this forum. Thank you, gentlemen, for your participation, advice, and reassurance.

01-06-2009, 21:14	#9
Chief Engineer Commercial Vendor Join Date: Aug 2006 Location: North of Baltimore Boat: Ericson 27 & 18' Herrmann Catboat Posts: 2,444	Not cranking when the engine is hot is usually a sign of a bad starter solenoid. If the windings in the solenoid are hot...the resistance goes up. Have you tried to jump the starter yet?