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Old 29 August 2007, 18:24   #1
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Engine fuse blowing Q

Hi team!

My Mariner 135 c.1988 has been playing up recently. It has started blowing the main fuse (starboard side of engine, 20A glass fuse) about once an hour. I think it tends to happen more when going fast in wavy conditions and playing the tilt position. The only other thing I've noticed is that the hydraulic tilt sometimes ticks (may be the relay?) when dropping the engine under power (although it may always have done this, only noticed now).

When the fuse blows, engine still runs okay, but trim/tilt, starter motor and rev counter don't work. Not immediately dangerous, but not ideal.

My mechanic guy is busy for the next couple of weeks, so was wondering if anyone had any idea what might be causing this. I have checked for loose wires etc, but cannot see anything unusual.

Thanks in advance!!
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Old 29 August 2007, 18:31   #2
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Might be worn brushes in the tilt motor. When they wear out the power consumption goes up.
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Old 29 August 2007, 18:42   #3
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Thanks Nos, would jolting due to waves accentuate the likelihood of a power spike?
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Old 29 August 2007, 18:44   #4
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Quote:
Originally Posted by bigNeil View Post
Thanks Nos, would jolting due to waves accentuate the likelihood of a power spike?
Not sure but you might be getting a pike through different degrees of wear on the commutator.
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Old 29 August 2007, 18:49   #5
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Thanks will look into this possibility.

Anyone else
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Old 30 August 2007, 10:38   #6
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Does it blow when you are actually using the PTT? Or randomly when out on the boat?
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Old 30 August 2007, 11:37   #7
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Jizm, sorry - cannot say for certain. It has gone almost exclusively when out in waves, and I do subconsciously trim and throttle up down quite a lot. You can't hear the trim motor at high speeds, and I don't have a trim gauge.

Having said that, there have been a couple of times when it has gone without using the trim control, e.g. when friends have been driving ("better not touch that"!), so may not be linked to the trim control at all (sorry, I'm useless ).
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Old 30 August 2007, 12:18   #8
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More likely a short under the cowl somewhere or maybe in the control box itself, have a really good look at all the wiring, especially in close proximity to moving parts. Check the state of the bullet connectors etc, if they are dirty and giving you a bad connection they will draw more current. Make sure no wires are clamped or crimped behind fittings or brackets etc. Have a look at the insulation and see if it has melted/rubbed off on the hot motor block. Make sure no earth rings have broken off and can touch on anything else causing a short etc etc...
Take your time and be methodical.
Good luck,
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Old 30 August 2007, 12:52   #9
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Thanks, I will have a much more thorough look tonight, nice evening up here
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Old 30 August 2007, 15:51   #10
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1st obvoius question to me is "is the fuse value correct". If this is the main fuse on the main supply to the engine, 20A seems low! Has to run the starter motor through that as well as charge the battery etc. On my 50, the main inline fuse is 40A.

Assuming the fuse is correct, what is the batt voltage when running at WOT? A faulty regulator could result in max power going to the bat at all times and would certainly load the fuse a lot. If voltage is over 14.4V, this needs looking at. Had a regulator / alterntor go in a car once that destroyed the main fuse either by causing a short or some other occurance.

Apart from that, shorts are also possible as mentioned before. It's not out the realms of possibility to have a short closer to the battery. If anything is shorted accross this the battery will also be shorted and things will get hot but the fuse would also blow on the engine as the alternator is shorted out.

What's the state of your electrical system? Is everything properly fused or are there some sneaky unfused spurs off the battery? What size is the cable from battery to engine? Is it all one piece or does it have joints in it?
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