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Author Topic:   Mercury 90-HP: Failed Rectifier-Regulator
Nauti Tauk posted 11-26-2008 07:45 AM ET (US)   Profile for Nauti Tauk   Send Email to Nauti Tauk  
What causes an outboard voltage regulator to go up in smoke? I have a 2003 Mercury 90-HP FOURSTROKE. I have two series 24 combination start and deep-cycle batteries connected by a VSR to help keep the trolling battery topped off. Although the batteries are different brands, they are approximately the same age. Both are wet-cell lead-acid. Replacing the voltage regulator is going to be expensive so I want to avoid any mistakes I may have made in the past. The only thing I question is my VSR. Thanks--Jerry
A2J15Sport posted 11-26-2008 01:30 PM ET (US)     Profile for A2J15Sport  Send Email to A2J15Sport     
The most common cause is a polarity switch.

In other words, someone, even briefly, crossed the POS+ and NEG- poles of the engine battery leads. That will do it, everytime.

Nobody will admit to it but is probably what happened.

Also, dirty battery connections (ENGINE END and battery end) can do it.

PAY SPECIAL ATTENTION to the ENGINE end of the battery connections. Nobody ever checks/cleans them.

jimh posted 11-26-2008 03:14 PM ET (US)     Profile for jimh  Send Email to jimh     
Production of smoke from electrical components usually indicates that their temperature has risen above the point of combustion of the material inside them. In general electrical devices abhor high temperatures, and the cooler they run the longer they last.

As mentioned, a reversal of the batter polarity will cause very high current flow, generally enough to lead to the destruction of most semiconductors in the path.

Solid-state electrical components also can be damaged by voltages which exceed their breakdown voltage ratings, and often this occurs with very brief or transient voltages which are produced. In an alternator device there is a lot of electrical energy stored in the magnetic field of the windings of the coils of the alternator. If this field is suddenly collapsed, as when a circuit is broken, it can produce a very high voltage spike. The condition is aggravated if there is not battery attached to absorb the energy. The exact situation occurs when there is a loose or intermittent connection to the battery, a condition common on boats because of the motion and vibration always present.

Questions about small boat electrical systems are best discussed in the SMALL BOAT ELECTRICAL discussion, and this article will be moved there.

If you are unfamiliar with generation of electrical energy in outboard motors, see:

Boat Electrical Power Generation


Permanent Magnet Alternators

outragesteve posted 11-26-2008 06:55 PM ET (US)     Profile for outragesteve  Send Email to outragesteve     
This is a known problem on the same Yamaha engines, 80-100 FS's. I changed 3 on one engine: Two caused fires, one major and Yamaha covered the dealer repair ($2,500) out of warranty. I do not know for fact that Merc used the same rectifier/regulator unit. It seems they overheat, melt the leads, and then if it shorts to ground it can cause a fire. I'd check with my Yamaha dealer. From myn understanding there was no recall, however, some dealers will tell you there is a problem, and in fact, certain production numbers stamped on the regulator housing were an indication of a potential issue. Good solid battery connections are a must, and never switch the battery switch with the ignition on. Good luck!
jimh posted 11-26-2008 11:39 PM ET (US)     Profile for jimh  Send Email to jimh     
Generating high charging current causes heat. If your boat's battery bank was always in need of charging, which can occur if you repeatedly use the batteries to power an electric trolling motor for long periods, then the outboard alternator has to produce high charging current. If there is anything marginal in the system, running for long periods at high current output will reveal the weakness.

As for the relationship between your Mercury motor and similar Yamaha motors, I don't know for certain if they use the same alternator. It is fairly certain that most of the power head in the Mercury motor was made by Yamaha, but generally Mercury re-fits these motors with Mercury electrical components. Is the alternator a pulley driven automotive type alternator? Or is it an under-flywheel permanent magnet alternator?

seahorse posted 11-27-2008 07:47 AM ET (US)     Profile for seahorse  Send Email to seahorse     

I believe that Yamaha has had at least 3 bulletins about changing regulators for one reason or another on their 4 cylinder 4-strokes in the 80 through 115hp range.
95Outrage17 posted 11-27-2008 11:59 PM ET (US)     Profile for 95Outrage17  Send Email to 95Outrage17     
Hey guys,

I think I can clear this up for you. I'm not quite sure as to the cause, but the regulator/rectifier on my 2004 Mercury Fourstroke 90hp started causing an overcharge condition last fall. My volt meter was showing about 18V at crusing speed. I priced the part and after I regained conscienceness I went over to my friend's house to borrow the one off his '01 Yamaha F100 that was awaiting some major engine work. It was exactly the same as the one I removed from my motor. I used the part off the F100 while I looked for a reasonably priced replacement. After some research I found out that the part had been updated (Merc would not cover it or admit to a problem) and it cost half as much from Yamaha as it did from Mercury. I bought the updated part from Yamaha and installed it in the spring. The new regulator/rectifier is quite a bit larger then the original which had burn marks on back (opposite the heat dispersion fins).

As a note; The Mercury and Yamaha versions of these engines are nearly identicle under the cowl. I maintain several of them. One block is blue/gray (Yamaha) and one is black (Mercury). Other then that the only differences are some of the engine harness attachments (cables, wiring harness). Outside of that it's model year differences. For example, I think the Yamaha F90 had fuel injection before the Mercury Fourstroke 90hp. Oh, the Yamaha takes 4.5L of engine oil and the Mercury takes 5L. The oil fiters are interchangable as well.

- Chris

fishinchips posted 11-28-2008 11:39 PM ET (US)     Profile for fishinchips  Send Email to fishinchips     
Chris (95Outrage17),
Can you give us the part number?


95Outrage17 posted 11-29-2008 12:09 AM ET (US)     Profile for 95Outrage17  Send Email to 95Outrage17     
Hi Ken,

This should be the updated version: 67F-81960-12-00. I simply ordered a regulator for an 2004 Yamaha F90. I often reference parts on As I mentioned, the updated part looks different then the original. It's larger, but the plug is the same and the bolt holes line up. I hope this info is helpful.

- Chris

fishinchips posted 11-30-2008 01:15 AM ET (US)     Profile for fishinchips  Send Email to fishinchips     
thanks for the info !


Jamber posted 12-30-2008 03:24 PM ET (US)     Profile for Jamber  Send Email to Jamber     
Then last night I took my boat off my boat lift from behind my house, I let the engine (Yamaha F100) warm up to temp, then drove it about 5 minutes (near idle speed) to the ramp. I put it on the trailer and then I parked my Whaler in the garage. I smelled a very faint electrical burning smell. I looked/sniffed around and could not find anything very strong. I checked my tow vehicle as well, could not find anything. I made sure everything was off. Figured it was coming from outside. I checked it a half hour later and could not smell anything.
When I took the engine cover off this morning (to change out my spark plugs)
I got another faint whiff of the smell. I looked/sniffed around again and could not find anything. I did not know what is was until I ran the boat after I put the new spark plugs in. The engine cover was now off so I could now see smoke pouring out of the front of the engine and had that same electrical burning smell. I shut it down right away. I took off some of the covers looked around and could not see where it was coming from. So with fire extinguisher in hand I started it up again saw the smoke and turned it off right away. The CDI unit and/or the Rectifier/Regulator appear to have been smoking. The CDI unit is slightly melted on the back side. I think I am lucky I caught it before it got fully engulfed and caused major damage.

I do not have any electronics installed, I cleaned my terminals about 5 months ago when I changed the did my normal service (oils and filters out).

I will investigate further.


95Outrage17 posted 12-31-2008 12:13 AM ET (US)     Profile for 95Outrage17  Send Email to 95Outrage17     
Hi James,

Glad to hear you were able to determine where the smell was comming from before something worse happened! I would contact Yamaha and tell them what happened and maybe that you're quite upset about it. You may also want to contact your local dealer as well. I realize the motor is almost 10 years old, but that could have been dangerous and that is a known problem with an updated part. They probably won't do anything, but it may be worth the effort. Good luck sorting this out, I'll be interested to know what the outcome is.

- Chris

Jamber posted 12-31-2008 08:27 AM ET (US)     Profile for Jamber  Send Email to Jamber     
Thank you Chris. Good advice. I am very upset about it. I will contact Yamaha and my dealer. So glad I did catch it early, and I was not out on the boat with my family when it happened, that would have been scary.

Do you think it is the regulator/rectifier that was the problem or is there something causing it to fail. Hate to put on a new $200 part and have it fail again. I checked my terminals and they all look good. Like I said I do not have any electronics, never had.


Jamber posted 12-31-2008 10:53 AM ET (US)     Profile for Jamber  Send Email to Jamber     
I just got off the phone with my dealer and Yamaha.

Dealer has seen this several times but has not had any support from Yamaha if the engine was out of warranty period. The dealer wants $225 for the rectifier/regulator (67F-81960-12-00) plus an hour ($90) of labor to go over the engine for band grounds/connections and install the new rectifier/regulator.

Yamaha said sorry, nothing they can do since it is out of warranty. I went on about how upset I was that this happened and it was a known issue with this part, I think they should offer me some support with this. They said sorry just like any other part that wears out over time - nothing they can do and suggested to try to go through my insurance company. Maybe I did not get upset enough! I doubt the insurance co. can do anything either. Sounds like it will come in under my $500 deductible. I may call - worst they say is "No".

My other concern is if the CDI got damaged, it was still running like smooth when the the smoke started. Could the CDI have caused short? The melted area of the CDI is at the top of the unit, furthest away from the regulator/rectifier. Here are some photos - any thoughts?

I am just happy I caught it early, it could have been worse, could have caused lots of damage, worse been stranded or even worse somebody could have gotten hurt.

The engine is almost 10 years old, did not give me an ounce of trouble the first 8 years, always started up on the first or second crank, always run smooth as butter. Then last year I dropped $750 into it to fix an oil pump seal leak. The ethanol switch a few months ago has made it run like junk (that is why I replaced the spark plugs). If this is annual thing, it may be time to think about a re-power.


PS. Here are links to larger images:

95Outrage17 posted 12-31-2008 12:28 PM ET (US)     Profile for 95Outrage17  Send Email to 95Outrage17     
Hi James,

I'm sorry to hear you didn't get any help from Yamaha. I think they should own up to this safety issue. I'm not surprised though, Mercury wouldn't help me with mine when it failed either. Although mine didn't start to smoke. I noticed an overcharge condition with my volt guage.
I am not aware of any problems with the CDI unit. Those bubbles on yours are odd. I wonder if it was overloaded by the regulator providing too much voltage? If this was the case and the unit seems to function fine then I wouldn't be too concerned about it with a new, updated, regulator installed. Another thing you could do is try to locate an undamaged, used, CDI unit. Shouldn't be too difficult and you could likely find one from a member here if you posted a wanted ad. Did you mention the melted CDI unit to your dealer?
An hours labor to replace the regulator is reasonable as the intake has to be removed to access one of the bolts. Unless the intake is shorter then the Merc version, it's hard to tell from the angle of the picture. Oh, as for the regulator/rectifier being the problem; I'm pretty confident it is. As mentioned, they are a known failure and have caused fires in some cases. Mine had burn marks all over the back of the unit. The updated version is much larger, I'm assuming to prevent the overheating problem. My Outrage doesn't have much in the way of electronics either, just a small fishfinder, which it's only had since 2007. I'm not sure that it really matters as the regulators seem to fail regardless.
As for problems and the age of the motor; That's up to you. In my experience, aside from the carbs fouling (low speed jets clogging) and regulator/rectifier issues, the only other somewhat common failure on these motors that comes to mind is the fuel pumps. They occasionally fail and allow fuel into the crankcase (small amount) thought a pin hole in a diaphragm. It's noticed by a rising oil level on the dipstick over time. I do have a question for you; Have the three engine block anodes been replaced periodically? I usually replace them every 2-3 years to help the motor fight internal corrosion. The only thing I can't answer for you is the ethanol issue. We do not have ethanol in our fuel here in Nova Scotia, so I have no experience with related problems. I think your engine has some good service left in it yet and you just have a few issues to sort out. If you do decide to repower, I'd just put on a new version of what you have. Friends of mine have an '06 Yamaha F90 EFI on their Outrage and it's even nicer then the older carbed versions. Instant starts, even quieter, smoother, better fuel economy and some updates (like the regulator/rectifier). Nice engine.

- Chris

Jamber posted 01-01-2009 03:53 PM ET (US)     Profile for Jamber  Send Email to Jamber     
Thanks again Chris for all the good info and sharing your experiences.

I would swap the rectifier/regulator our myself, but I think it worth the $90 to have the dealer do it and check for bad grounds. I did mention the CDI melted issue and the dealer did not think it would need to be replaced if it was running fine but said he will check it out.

I replaced all the anodes at 4 years then at 8-1/2 years. I also flush the engine with fresh water EVERY time after being in salt water. I also spray the block and wires etc.. with a good coating of silicone spray several times a year.

If the plugs don't smooth out my engine at idle, I will look into the possibility of the low speed jets being clogged. I did not get a good chance to see how it ran after plugs with the rectifier regulator issue.

Have you ever replaced the timing belt on one of these? I routinely inspect it for tension and wear. Mine looks pretty good - but it is original.

My plan is to fix it and keep it for at least a few more years. I would be happy to get 13+ years of reliable service out of this one. By then I will be ready for a larger boat as the kids get older. Right now our 16 Dauntless is a good size for us.

Happy New Year!


95Outrage17 posted 01-01-2009 09:37 PM ET (US)     Profile for 95Outrage17  Send Email to 95Outrage17     
No problem James, glad I could help a little and Happy New Year to you as well!
Sounds like you've taken good care of your Yamaha and I think your good service life expectancy for it is very reasonable. It should last a lot longer then that with the sort of care you're giving it. I wish I had the luxury(convienience) of flushing my Mercury after every time I use it. It's usually at a mooring that doesn't allow me to do so. I certainly flush it whenever it's on the trailer though. Anyway, that and regular replacement of those internal engine anodes will certainly help with corrosion in the cooling passages. Your engine looks like new under the cowl in those pictures.
As for smoothing out your idle; if the plugs don't work, then try spraying some carb cleaner into the intake with the engine running at idle speed. You'll have to bump the throttle a little (maybe 1200 - 1500 RPM) and it'll stall a few times probably, but it's worth a try. It may not work, but it did seem to help for me with a 2003 Mercury 90 4-stroke that had a low idle (stalling) problem. We'll see if the problem is totally gone in the spring when the boat is back in the water. The bottom carb is apparently the one most likely to have a problem if that helps.
I have not replaced the timing belt on one of these motors yet (mine still appears new). A good friend of mine has though (he also rebuilt an F100) and he said the belt is quite easy as long as you have a puller for the flywheel. I might replace the belt on mine before the spring just for piece of mind and knowing the engine has a fair amount of hours. I believe 1000 hours is the replacement interval.

- Chris

Jamber posted 03-09-2009 11:58 PM ET (US)     Profile for Jamber  Send Email to Jamber     
Update: I had my Regulator / Rectifier on my Yammie F100 replaced ($130 total). The CDI unit checked out fine, problem fixed. I had this done back in January, but just came across the photos and wanted to share the photos and give an update in case anyone else has this issue.

Update to the unrelated problem to the regulator/rectifier It is also running a bit smoother better with the new spark plugs, Yamaha Ring Free Fuel Treatment, fuel filters and some carb cleaner. I think I could still use a carb rebuild.

Thanks again for the tips Chris.

Here are some photos of the bad regulator/rectifier (not pretty and yes it smelled nasty:


Tohsgib posted 03-10-2009 01:36 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Also...NEVER switch from one battery to the other while engine is running. It will fry the regualtor in a heartbeat. I hate battery switches for this one reason because if the connections get dirty and it shuts off the battery when you hit a wave or something and then reconnects, fried regulator again. Or your battery is dead so you switch it both then back again to charge once running, it "may" do damage. If your tach or volt meter start working strange, chances are the regulator/rectifier is bad.
95Outrage17 posted 03-10-2009 07:02 PM ET (US)     Profile for 95Outrage17  Send Email to 95Outrage17     

Glad you were able to get the regulator/rectifier replaced at a reasonable cost. $130 is a good price. Although, I think they should be replaced for free (recall). Looks like the old one was pretty fried! Good to hear that your problem is solved and you can continue enjoying your Whaler. Thanks for the update!

- Chris

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