Engine Won't Start because fuse blown

[Vincentc]

Part of our boat ride included a trip to Mary Walker Marina to buy fuel for the trip to the Gulf Coast Rendezvous in May. After fueling, the port engine, 671 TI would not start, in fact when I turned the key nothing happened. After several unproductive efforts I started checking with an electrical meter. I had a hot battery, but no voltage at the starter. I then checked the battery on/off switch; there was voltage going in and none out. Looking further I discovered there was a 50 amp fuse (a cylinder about ¾ inch diameter and 3 inches long) just below the switch. The boat is a 43DC 1983, I do not know if this arrangement is OEM.

The tester indicated the fuse was blown. The marina didn’t have any fuses for sale but the owner offered and I accepted a ride to Lowe’s and I found a fuse, which matched the old one and cost $12 for a pair. With the replacement fuse installed the engine started fine and the trip home was uneventful.

Thinking about what might have caused the fuse to fail, I recall that startup was uneventful; however, the voltmeter was not working the first time I checked the port engine gauges. When we arrived at Mary Walker the port engine would not shut down, and I had to lift the hatch and move the linkage by hand. I used the battery parallel switch to turn the engines with the shut down switch engaged before actually starting and both engines started immediately.

In addition to sharing what might be useful information, I’d like to know why the fuse failed and if this indicates an underlying electrical problem, what might be the cause?

Thoughts or suggestions please?

 

[Genesis]

I'm not sure which fuse you're referring to exactly but the power feed to the ignition key (which feeds the shutdown and start buttons) is fused, and it's a relatively high-power fuse (50A sounds right) as the starter solenoid and especially shutdown solenoid require a fair bit of power.

An intermittent short is likely, assuming the fuse didn't fail due to mechanical stress (vibration, etc) over time - that's not particularly common but it does happen. Finding intermittent faults like this is a lot of fun...... I would inspect the wiring in the starter and shutdown circuits to see if you can find anything frayed or otherwise out-of-sorts as a starting point.

 

[TopHattandTails]

How are the batteries? Old? Burning water? Does the fuse blow on only 1 side or does it travel to both motors/ fuse panels?

 

[Canuck Dennis]

I had the same issue just after I bought the boat, 6-71's N series, the fuse blew for no apparent reason, replaced it and no problems since , close to 3 yrs now. Maybe the original fuse was just "tired"

 

[Vincentc]

Thanks Karl,
The fuse is located under and adjacent to the rotary on / off battery switch for that engine. The battery cables going to and from the switch are substantial perhaps 3/4" od. The cables going to the fuse holder are smaller, perhaps 1/2" od and I believe the cables to and from the fuse run from one of the 3 poles on the battery switch to another of the three switch poles.

I have found that the connection on the battery switch for the large cable which runs from the switch to the starter was a little loose, the nut was snug on the lug but you could move the lug around on the switch terminal by hand so I tightened the nut perhaps 1/8 turn.

 

[saltshaker]

I had the same issue just after I bought the boat, 6-71's N series, the fuse blew for no apparent reason, replaced it and no problems since , close to 3 yrs now. Maybe the original fuse was just "tired"

Same here. I blew one about 6 years ago. Checked out everything and all was OK. Haven't had to change one since.

 

[Vincentc]

Thanks for the additional comments. Even though 2 show an earlier time than my reply they did not show up on my computer when I replied to Karl.

The batteries are new, the fuse is old. I feel better knowing that there are others with similar experiences.

Although I have been operating and maintaining diesel boats for over 30 years, I didn't know till yesterday that there was a fuse for the starter solenoid. I discovered it by accident when turning the battery switch and looking for something wrong. Even when I found it, I was doubtful that this was the cause.

Not knowing these kinds of things could be costly.

 

[REBrueckner]

Fuses blowing in a marine environment for no apparent reason is common.

The usual cause is oxidation between the fuse and the fuse holder....as points of oxidation begin to carry current, they heat and the fuse link melts..

The cure: rotate ALL fuses in their holder at least annually. This scrapes off any oxidation. I've posted this numerous times before and also recommend such rotation be a part of your regular pre season maintenance.

I had a bilge alarm fuse down deep in my bilge and if I did not rotate that to scrap it clean it failed annually. I could understand that because of the moist environment there. But for some reason, I experienced the same type of fuse failure inside my flybridge where there was a fuse panel feeding flybridge electronics.