Fire-Fire!!

Started up my Diesel for my weekly check last night and saw smoke coming out of the engine room within 30 seconds. A quick look revealed a small fire (looked huge but was only the size of a Brillo pad)) in the wiring hardness next to the oil pressure sending unit. Since I have 6 fire extinguishers on a 37' boat one was within easy reach. One short blast and the fire was out.

Cause of the fire was the oil sending unit went to ground as soon as the switch was made. The hot side wire of the osu completely melted and luckily no other wires in the harness were damaged.

Lessons from this? Always-always keep a clean engine room. This could have turned out to be much worse.

Wow! Glad to hear you saved it so quickly.

Oil and coolant alarm switches are usually powered from the engine "ignition" circuit which is fused. Yours wasn't?

David

Oil sender lead can be grounded and all it should do is change gauge reading. Something else caused the fault/fire.

+1 on Ski’s comment.

+2 on Ski's comment.

Keep looking.

That's a great question. I'll have to check on that asap.

Just curious, what kind of fire extinguisher did you use?

Wow! Glad this turned out well!!! I’m changing the oils this week and will certainly keep this in the back of my mind! Great advice!

Man that is why I hired a pro to wire all my 12 volt, that kinda thing scares the crap out of me. I’m glad it turned out good for you. I always looks for vibration wear in the wires, something big (amp) shorted out something small (wire ground)

Is it per chance the original wiring harness? If so, maybe after half a century it abraded itself a bit too much.

Nordic Star said:

Lessons from this? Always-always keep a clean engine room. This could have turned out to be much worse.

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I apologize as I'm a bit slow. How did an unclean engine room cause this fire?

Very glad to hear you are OK. Fire can happen in the least expected locations.

Shrew

What I meant by that was if my engine room had been dirty with oil, dust and grime the fire could have grown quickly.

I keep a clean engine room so there wasn't anything else the fire could spread to.

I'm rethinking the cause Thanks to some great comments here. The starter wires run right through that harness so there's my first check.

The more I look at that harness the more I want to rewire. BIG job but better than fires.

The more I look at that harness the more I want to rewire. BIG job but better than fires.

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Glad you made short work of it.
Absolutely agree...not much worse than fire in a melting object full of fuel.

Often there is an oil pressure activated switch that Is used to supply power to another device. When I purchased my current boat I found I had 1 on each engine with NO fuse. There should be a fuse at the source.

Ken

Nordic Star said:

I'm rethinking the cause Thanks to some great comments here. The starter wires run right through that harness so there's my first check.

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That sounds much more likely.

Hopefully the fire hasn't destroyed all the clues to the cause. It is always nice to be sure of what caused a serious issue such as this.

Fire Extinguisher used

HopCar said:

Just curious, what kind of fire extinguisher did you use?

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I used the Powder. I know CO2 would have been just as effective and a lot less of a mess but nonetheless I used the nearest extinguisher.

Nordic Star said:

I used the Powder. I know CO2 would have been just as effective and a lot less of a mess but nonetheless I used the nearest extinguisher.

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The important thing is it worked. Was it as hard to clean up as you hear?

Do you have an automatic halon system? If you do, investigate why it didn’t go off.

Donna said:

Do you have an automatic halon system? If you do, investigate why it didn’t go off.

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I’m guessing because he got onto it so quickly and put it out manually. At least as fire suppression systems go, its cheaper to replace a small fire extinguisher than to re-and-re a halon system.

Unless you have a very specific requirement NEEDING Halon you cannot get them refilled.
You can use an existing unit but once used it must be replaced with something different.

I had a halon unit years ago for the previous boat, gasoline powered.. On this boat it was useless so I gave it away. My now engine is diesel and the engine compartment is too darn big for that halon unit to do any good so it was just useless baggage.

C lectric said:

Unless you have a very specific requirement NEEDING Halon you cannot get them refilled.
You can use an existing unit but once used it must be replaced with something different.

I had a halon unit years ago for the previous boat, gasoline powered.. On this boat it was useless so I gave it away. My now engine is diesel and the engine compartment is too darn big for that halon unit to do any good so it was just useless baggage.

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My boat is diesel and my halon system is large enough for my large engine room. I have a friend who is the fire chief where I live and I asked him to inspect the system. He told me the system was totally larger enough and I have it reinspected every year.

Donna said:

My boat is diesel and my halon system is large enough for my large engine room. I have a friend who is the fire chief where I live and I asked him to inspect the system. He told me the system was totally larger enough and I have it reinspected every year.

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I think C’s point is, you can get it inspected but (at least in Canada) not refilled. Not sure about what you can do stateside with grandfathered systems. So, your better off putting out a fire with a portable system first if it is safe to do sound within your on capabilities, and save your Halon system for more dangerous fires,

Yes, JD Cave has it right.

If you have it you can keep it. But if it is ever used you most likely will not be able to get if refilled. Yes, where you are Donna, the rules may be different so you should ask your friend. I'll guess yours will not be refillable if you ever do use it. But if you need it use it as many boat fires have a very limited time to get them under control.

Note also that a diesel could care less if a Halon system triggers. It will continue to run and burn the Halon. Auto Halon systems , for that reason, almost always were tied to the engine to automatically shut the engine off.
Too boot when the engine burns the stuff it changes into a poisonous gas [don't remember which] although unless something is wrong with the exhaust that should be of less concern than putting the fire out FAST.

Just be sure the engine shuts down when the system is triggered. At the very least a LOUD alarm so if it is not automatic shutdown you are aware you have a big problem.

Found the cause of the fire. It was an old 4 pin relay that had the coil fail or short. This relay is used to sound an alarm should I get a hi tranny temp, a high engine block temp or low oil pressure. These 3 alarm points provide the ground to the relay which in turn energizes an audible alarm. When the coil shorted it sent 12v down to these switches (alarm points) and grounded out. There wasn't a fuse in this 1969 vintage wiring but there is now . I am really lucky in that the only damage was 12" of melted wire.

Nordic Star said:

Found the cause of the fire. It was an old 4 pin relay that had the coil fail or short. This relay is used to sound an alarm should I get a hi tranny temp, a high engine block temp or low oil pressure. These 3 alarm points provide the ground to the relay which in turn energizes an audible alarm. When the coil shorted it sent 12v down to these switches (alarm points) and grounded out. There wasn't a fuse in this 1969 vintage wiring but there is now . I am really lucky in that the only damage was 12" of melted wire.

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Pleased you found the circumstance. Good lesson for all who follow this thread. Thanks for posting!

Well done in tracking it down, NS.
You can sleep easier now, instead of wondering if there could be a repeat performance.