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Discussion Starter #1
hi there, the OVP fuses keep blowing out in my 91 300E 2.6... Like twice a week. The OVP is new. Does anyone know why? Did a search- the only info I could find is that there might be a stripped wire making contact. Thanks in advance..
 

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How many miles are there on the current alternator voltage regulator?
 

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sergio- thanks for the reply.. the voltage regulator has a LOT of miles... like over 274,000 miles. I believe it is original but cannot confirm.

I Didn't replace it because I thought the lights dimmed and the wipers slowed down before the V.R. was about to crap out.

Could this be the cause? That would be great news if it is, because I am not looking forward to tearing apart the car looking for a stripped wire..

Over the course of the month I replaced distributor cap, rotor, spark plugs, both fuel pumps, belt tensioner, OVP, spark plugs, belt tensioner, tensioner shock, mono valve assembly, thermostat, air filter, fuel filter, eibach springs, kyb's, and more just to get it back on the road... So I'm very frustrated...

Anyone else wanna chime in? Thanks in advance...
 

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Monitor the battery voltage at about 2000 R.P.M. If over 14.5V, you need to replace the voltage regulator. With that kind of mileage, I would replace it anyway (it is a very inexpensive part).
 

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the voltage regulator is not a wear item. It is electronic. Mileage is not a consideration for replacement. Voltage at 2000 RPM (off idle) is the concern. It will vary some with temperature, but anything over 15 volt is definately too much. Replacing because of mileage makes you as bad as the "part swapper" mechanics that just replace parts until they solve it. Not a good way to fix a car especially if it is your money you are spending. Some of the old Chilton repair manuals have a good section on troubleshooting charging systems (make sure your get one that refers to eletronic - some very old ones have the old mechanical regulators). Newer manuals don't have much about it because after around the mid seventies the regulators became integral with the alternator and no longer easily serviceable. GOOD LUCK.
 

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The brushes on the VR are most certainly a wear item. Sergio's recommndation to change mine last summer saved my butt.
 

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Discussion Starter #7
All- thanks for all the replies...

Put new fuses in again last night and predictably, they blew again this morning... Bit of an update on the symptoms...

Car starts fine, shift from park to reverse to get it out my spot, and when I put in Drive, the ABS light illuminates and the usually one of the fuses blow. Engine bogs down when I accelerate until it is warm.

Anyway, I'm gonna test the V.R. tonight... Hopefully this will be the end of the problem. If not I'm gonna push it into the Hudson river.

I'm open to any other suggestions on the fuse problem.

I'll report back my findings once this issue is resolved so there'll be some solid info the archive searches...

THANKS.
 

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the voltage regulator is not a wear item. It is electronic. Mileage is not a consideration for replacement. Voltage at 2000 RPM (off idle) is the concern. It will vary some with temperature, but anything over 15 volt is definately too much. Replacing because of mileage makes you as bad as the "part swapper" mechanics that just replace parts until they solve it. Not a good way to fix a car especially if it is your money you are spending. Some of the old Chilton repair manuals have a good section on troubleshooting charging systems (make sure your get one that refers to eletronic - some very old ones have the old mechanical regulators). Newer manuals don't have much about it because after around the mid seventies the regulators became integral with the alternator and no longer easily serviceable. GOOD LUCK.

WRONG!!!! The voltage regulator has brushes that do wear with use. Have you ever taken one apart? I did and it was worn all the way down. It is good advise (and this comes from a MB mechanic with 30+ years of experience) to replace them every 100K miles. And, by the way, the part you are throwing at it costs about $25. Small price to pay every 100K miles, don't you think?
 

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Discussion Starter #9
WRONG!!!! The voltage regulator has brushes that do wear with use. Have you ever taken one apart? I did and it was worn all the way down. It is good advise (and this comes from a MB mechanic with 30+ years of experience) to replace them every 100K miles. And, by the way, the part you are throwing at it costs about $25. Small price to pay every 100K miles, don't you think?

-Agreed.. Already ordered the part. I'll report my findings...
 

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I stand corrected. The brushes certainly are a wear item. Since MB puts the brushes with the Voltage regulator electronics, they need to be changed together. (If it was designed like most alternators, the brushes would be separate) Still do the necessary homework before you throw the parts at it. Another good item to check would be the wires to the alternator. I have seen problems with the wiring on many cars which resulted in an alternator being replaced and the problem persisting.
I just get a little concerned when people tell other people just do this or that and don't give them the logic. I wouldn't be eating crow right now if it was stated that the voltage regulator requires replacement because the integral brushes may be worn out at this type of mileage. If I answered that I would have stated that your brushes may be worn and that the voltage regulator which is intregral should be replaced - Just to say the voltage reguilaotr is bad because it has so many mileage - doesn't pass the sniff test!
 

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Correct. The voltage regulator needs to be replaced IF the voltage exceeds 14.5 volts because its brushes are worn. If they aren't, it is a good idea to replace it every 100K miles because when it fails, it can make your vehicle go into limp mode (if equiped with ASR) and then it's a PITA driving back home (don't ask me how I know...)
 
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