Yanmar 3JH4E starting issues - Sun Oddysey 39DS

Jun 24, 2025
2
Jeanneau 39 DS Edinburgh
We have an intermittent issue on our boat where the engine won't start.

Usually, in the morning the engine starts first time, no problem. However the issue arises after we have had the engine on for a while and then turn it off and then try to turn it back on. If we give it a few hours to "cool off" the engine will regain it's sense of humor and turn on again, not good. When we turn the key either we are greeted by silence or one singular click.

Not entirely sure what the issue could be. What confuses me is why it will turn on in the mornings, this makes it tricky to demonstrate the issue.
 
Nov 6, 2006
10,093
Hunter 34 Mandeville Louisiana
Welcome to the forum! Much good information here in the General Downloads section.
Your problem is most likely a bad electrical connection that could be anywhere between the battery and the starter motor. On Yanmar, it is usually in the voltage supply to the starter solenoid, but without trouble shooting it is a shot in the dark. Time to get a voltmeter and start checking connections when under electrical load, not just when turned on.
 
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jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,143
CAL 35 Cruiser #21 moored EVERETT WA
:plus: Your description could be associated with a questionable electrical connection in the starter system.
When the engine is cold, the metals allow the circuit to provide the needed electrical power to start. When you warm up the engine, the loose connection is heated (expanded), creating an open circuit condition.

You get a low battery voltage type symptom: "When we turn the key, either we are greeted by silence or one singular click."

All this is the best SWAG. Loose connections are one of the usual suspects for what you describe.

Checking the connections is an easy task to accomplish. Be sure to disconnect the battery before working with metal tools near electrical connections.
 
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Jun 24, 2025
2
Jeanneau 39 DS Edinburgh
So I have found that when hot there is no power getting to the white cable that plugs into the starter motor. When cold there is, so the problem must be before that.
 
Jun 17, 2022
236
Hunter 380 Comox BC
Good job! The Yanmar wiring harness is plain copper. As it ages, tiny breaks occurs in the wires due to age, vibrations, heat, salty air, chafing, etc... causing intermittent connections. If your white wire is suffering, the rest are not far behind. I'd suggest replacing all the engine wires with marine tinned wire. You can buy a new Yanmar harness, but it will also have plain copper wires. For about half the cost and 2-3 days work, you can make a new harness with better quality wire (minus the harness connectors at the engine and behind the engine panel). While you do that, it would not hurt to go up one size on the white wire, since the voltage delivery to the starter solenoid must be high enough to activate it.

Wires to replace:
12V to instrument panel (usually comes from the large positive terminal on the starter, through a 30A fuse)
ground to instrument panel
high temp switch
low oil pressure switch
ignition (white)
alternator exciter
air intake heater (if equipped)
oil pressure (if equipped)
coolant temp (if equipped)

The 12V and the ignition wire should be fairly large, 10AWG ideal, 12AWG at the minimum.



Can you confirm someone was turning the key/pushing the start button while you tested the white wire at the alternator?
 
Last edited:
May 24, 2004
7,173
CC 30 South Florida
It is a regular and known malady for Yanmar engines. Over time the wiring from the control panel to the starter solenoid fails to deliver the minimum voltage to activate the solenoid. The fault starts at random and then progresses to the point of total failure. The fix ranges from cleaning the connector points to replacing wiring harnesses, solenoids and starters. Many have solved the issue by stringing a new set of wires alongside the existing harness replacing those in the harness, Another solution I have seen and the one I have taken is installing a 2nd start button wired in parallel, somewhere inside the cabin near the engine compartment. With a shorter wire run and taking power from a different location the 2nd button can be used to start the engine in those instances when the primary button fails. Its located inside the cabin to prevent anyone from hoping aboard, starting the engine and taking the boat. No big deal just walk a couple of paces start the engine and go back to the helm. The diagnosing and the fixes can be frustrating it seems that with time the connectors and the wiring fail to deliver the voltage in conjunction with solenoids and starters that may require more power than they used to. Our primary button still works, it is hit and miss but that 2nd button has never failed.
 
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