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So, I have gone through several (actually have last track of how many) alternators on my 2006 Merc 250xs. Working with the factory folks, my mechanic has checked every possible cause. In fact, I have elected to have several items replaced in an attempt short-circuit the hidden gremlin. Another alternator began to fail this past weekend (only two hours on it). The Mercury Technical Representative for my mechanic has proposed that there is a possibility that the on-board charger could be the cause of the problem. He has suggested that it is possible that a diode/s or solid state device has failed creating a reverse discharge scenario which would essentially cause the alternator to work overtime and fail prematurely.So, has anyone experienced, or know of someone, that has experience a similar situation (alternators failing after 2-5 hours of use) with the cause being being a faulty charger? As you can imagine, it is quite frustrating.Any thoughts would be greatly appreciated. Thanks.
If the charger was discharging your cranking battery then it wouldnt start when you put it in the water. The Optimax needs a lot of cranking amps to start it and a half dead battery wont do it. If they are stuck on that though unhook the charger from cranking battery tell them to put another alternator on it and see how it does.
You are correct; however, the batteries are always at a full charge prior to launching and there never is a problem starting the motor despite the “juice” that the Optis need to turn over. What you have suggested (i.e., remove the charger) is exactly what has been suggested, by Mercury, as our next step. I am testing it tonight to see if that is the fix we have been looking for. It is Mercurys belief that the alternator may still be good enough for this test. Once the alternator begins to fail, an increase in load (i.e., increase in rpms) sends the Guardian System into action and you are politely (haha) informed that the voltage is low (begins in the 11v range). It is going to be interesting to see if the GS “talks” to me tonight. If it does not work the next step will be to install a new alternator and start the test all over in the company of a Mercury representative.
I have had mercruiser style alternators built by a pro that does this stuff with higher amp diodes. Boats these days have high electrical loads with all the on board electronics.I doubt that the on board charger is the problem. Disconnection it is one of the first steps in trouble shooting the problem.Have your batteries load checked. Have the alternator checked.Then start connecting loads.A short circuit will cause heat, smoke, and melt insulation.Solid state electronics failure mode is open circuit.
We have seen no issue on this and are not sure if that charger is working how it could cause that. This would be a question for Rick S. at NOCO. You could also disconnect it and try charging your battery manually since it will be out of warranty on the charger. If it work you loose nothing there and figure it out. Though we are not sure how that would impact the alternator. There is no voltage bump>? BCB
Well the problem has finally been diagnosed. It is never good when your mechanic calls and says “I have some bad news.” I figured come on, how bad can it be….bad.No matter what boards I visited or who my mechanic would consult with, the focal point of all of the suggestions was the electrical system (shorts, etc.). Too bad the problem was not a wiring issue, as that would have been cheap compared to having to replace a powerhead. Yep, there is a crack where the block is welded together, directly below the alternator. Water and alternators are not the best of friends….imagine that. So, it turns out, according to Mercury, there have been some reports of weld failures on the blocks. In fact, we found out that there is a guy that went through 17 (yes, 17) alternators before the crack was identified. After doing a search on this site, I did find an individual that was having alternator problems. Evidently Mercury sent folks from the factory to look at it and they could not figure out what was contributing to the failures. Fortunately for that individual, his motor was still under warranty and Mercury waved the white flag and provided him with a new motor. I suspect they were dealing with a similar issue. As for me, the warranty expired prior to the problem started……looks like I may have to wave the white flag but not before some pleading and begging.
That sucks, I have been there. Mine was out of warranty by a couple months but this was back in the opti-pop days so they replaced it free of charge. I hope it works out for you. Mercury was making remanufactured Optis for a while and the price was about the same as a new powerhead. That plant was next to ours and it is closed now so I am not sure if they are still offering that or not.
As has been said, disconnect the charger. I would be more suspect of a faulty voltage regulator though, or bad battery lead calling for max output and cooking the alternator.
Bummer out of warranty. I did not know Mercury had welds on the block to hold things together.I thought everything was cast and machined.If it is just a water jacket (water you are trying to suppress) you might be able to JB weld it.I have done this with great success on OMC looper heads. The water jacket would crack on the head and I would JB weld it.Paint over it and no one but you will know it is there.
The blocks are all cast alum in the lost foam process, there may be a foam seam though no weld on the block.
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