Early Warning for W124 Alternator Failure

[Savannah Buzz]

My 93 300TE has displayed rapid changes in the coolant temp, from about "78" to about "88", like a light switch. I thought I had a skinned wire grounding out, or maybe a sticking thermostat, or a slipping belt.

So I tightened the belt, did not back off the tensioner lock bolt enough, stripped the adjustment. Replaced tensioner, found fan bearing bracket bearings failing, and also water pump hard to turn. Replaced both (water pump is an all day activity). And replaced original thermostat twice.

Finally would stay on about 78 most of the time. Then on the way to work, ABS light on, then SRS, then AC shuts off, then starts running rough, then dies within 1/2 mile. Voltmeter on battery reads 6.5 volts.

Turned out to be alternator brushes, which of course never caused idiot light to stay on. But from an electrical standpoint it makes sense. As the brushes touched or did not touch, the voltage changed quickly, and the guage responded, being a simple series circuit.

So if your coolant temp on a W124 is twitching, reach for the back of the alternator. One of the few places under the hood with plenty of space to work... And the regulator / brushes are simple to change - two screws. By the way, the voltage across the battery won't be the 14.1 - 14.2 you might be used to on Detroit iron. MB at that time liked 13.6. And now my temp is 88 (splits the top of the 8 in 80).

[stormyc88]

Do you think this would apply to an 87 like mine? I'm not having problems, but its good to know the warning signs.

[engatwork]

Welcome aboard Savannah Buzz.

[big dog 2]

Originally Posted by stormyc88

Do you think this would apply to an 87 like mine? I'm not having problems, but its good to know the warning signs.

My charge light flicked on and off from time to time. I took out my old voltage regulator and found the brushes worn down about 50% after 113k. A new regulator seemed to fix the issue. Noticed the voltage was a bit under 14 volts too but was good enough! Simple repair!

[Matt L]

If your (electric) temperature gauge fluctuates during varying alternator load, it means that the engine-to-body ground is faulty.

The sensor is grounded to the engine, and the gauge to the body. A faulty ground causes the engine to be at a different potential than the body.

So you fixed one problem, but another remains.

[glenmore]

Which grounds would you check?

Thanks.

glenmore
1991 300CE
1999, 2000 C280
2000 C230K

[JohnM.]

I've had this happen multiple times when my stock alternator was eating brushes. Car ran almost 40 miles on battery power each time (go Optima!). Started with one idiot light and then the rest tumbled. Was able to drive for about 15 minutes once all the lights came on.

The OP's problem with the coolant gauge was resolved with a new alternator. I recall having similar twitches with the coolant gauge when my brushes were going out.

[balge]

Hmm, my '93 300TD was giving 14.2V with an original looking Bosch regulator even with worn out bushes, the replacement regulator gave 14.0V....

Not having a thermostat in it when I got the car used to cause the temp gauge to flutter wildly though.....

[lkchris]

My early warning was cruise control shutoff at 70 mph. Got my attention.

[jmbeam]

Hey guys my 95 e300D has its temp gauge go very high, over the redline limit but when I flick the glass with my finger t drops back down. The oil pressure guage also stays at the upper limit but does not move. Could this be a simple ground problem? My SRS is also now staying on.

I was going to take the cluster out but havent had the time to do so yet.

[dieseldiehard]

OK, well my first comment is that the electrical oil pressure senders for later model Mercedes are sometimes flaky, that is they can give errors as they age and I've even seen a brand new one that was flaky.

Always remember that at initial point when the key is switched to pos.II "ON" the instruments lights all come on, with some exceptions on some vehicles, to act as a lamp check as well as letting you know the alternator regulator is operational.
If the brushes wear down completely then you have no lights with the initial switch "on" and if the battery is still charged you can start the car but its not going to stay charged for long especially if a diesel because the glow plugs will drain a battery pretty fast. OTOH a diesel without headlights on will run along way before the battery is discharged, compared to the gasser that needs a lot of current to run the spark and computer stuff.

The thing to do when performing regular annual maintenance if you want to prevent having a dead alternator for example in the winter or when on a long trip is to remove the regulator as Savannah Buzz recommended and inspect the brushes.

I recommend buying a Transpo 14.1V regulator, forget the factory Bosch its the same quality and I think you know about the prices...
Transpo's adjustable model p/n1B373A-1 fits the early W124 alternators. This model will allow one to adjust the charging voltage to whatever value wanted by using a tiny screwdriver (I use a jewelers screwdriver) to adjust a potentiometer thru a small hole. They didn't provide it but I used an adhesive "dot" to cover the hole after setting it to keep crud out.

As I recall the ones I have installed came pre-set to about 14V so I just left them as received.

Most alternators will provide a second or third life with only changing the regulator but if your alternator makes any high pitched sounds while turning (or bearing rumble) or if you examine the slip rings (copper rings the brushes ride on) and they have really deep grooves in them then it might be advisable to have it rebuilt. I've saved lots of $$ by replacing the regulator and never had one that gave a problem.

Order a Transpo now and have it on hand for your car or your shop because they may be hard to get when you need one (this is not something a PepBoys is likely to keep in stock!).
here's the link to a discussion of the Transpo and although written about the W123 cars, it gives links to Transpo's website:
Transpo Adjustable Voltage Regulators
DDH

[dieseldiehard]

sorry I didn't check thos links from the archived thread as they seem to not work. OK, maybe Google Transpo and see if they sell thru a dealer, I recall ordering from a place in NY but its been a few years.
I still have a 1B373a-1 here in my hot lil hands keeping it warm until the next alternator in my fleet takes a dump

[bchhabra]

Need some help here...Had cold start problem with my son's 1989 300E. Then stalling and died a few times at college. Jump started it and brought it home. Thought it was the battery since it would'nt hold a charge and my son complained of sulfur smell and fumes from the battery area. Replaced it with a brand new one. Still cold starting and stalling. Checked OVP relay - fuse was blown - replaced it and it blew again without the car being turned on so checked the relay and it was really bad. I replaced with a brand new OVP relay from ******** on Monday. While I was at it I also replaced with a brand new Bosch Voltage Regulator from ********. Car starts and runs fine now but I noticed alternator is producing 17.5V at battery so obviously something still wrong. I removed and reinstalled original Voltage Regulator (brushes were about halfway down) - still 17.5V. Put the brand new one back in - still 17.5V. Most posts I have seen talk about LOW Voltage conditions from Alternator - I have the reverse - HIGH voltage condition. I am pretty sure 17V is not good for the battery so I am not driving the car.

Any suggestions on why I am getting 17.5V and if I should replace the alternator or try to buy yet another Voltage Regulator? I am in Potomac, MD - anybody near by want to help this long weekend?

[JohnM.]

Originally Posted by bchhabra

Need some help here...Had cold start problem with my son's 1989 300E. Then stalling and died a few times at college. Jump started it and brought it home. Thought it was the battery since it would'nt hold a charge and my son complained of sulfur smell and fumes from the battery area. Replaced it with a brand new one. Still cold starting and stalling. Checked OVP relay - fuse was blown - replaced it and it blew again without the car being turned on so checked the relay and it was really bad. I replaced with a brand new OVP relay from ******** on Monday. While I was at it I also replaced with a brand new Bosch Voltage Regulator from ********. Car starts and runs fine now but I noticed alternator is producing 17.5V at battery so obviously something still wrong. I removed and reinstalled original Voltage Regulator (brushes were about halfway down) - still 17.5V. Put the brand new one back in - still 17.5V. Most posts I have seen talk about LOW Voltage conditions from Alternator - I have the reverse - HIGH voltage condition. I am pretty sure 17V is not good for the battery so I am not driving the car.

Any suggestions on why I am getting 17.5V and if I should replace the alternator or try to buy yet another Voltage Regulator? I am in Potomac, MD - anybody near by want to help this long weekend?

Replace the alternator.

[compress ignite]

after two different regulators.

What Brand of Regulator did Auto Unmentionable throw in the box they sent to you ? "Uro" throw it in the trash and get a Bosch regulator.