Hi guys,
Had the 240d all loaded up, fueled, and ready for my 700 mile thanksgiving trip, and the battery was dead. I had to take another car. Wouldn't it figure.

I was able to determine that the car isn't charging. Battery is brand new, alternator is new, wiring is fine and even though it's the third alternator in 4 months, the car had been running just fine for a month or so. Voltage regulator is also brand new.

The only thing I can think of is occasionally, maybe once a day, the glow light flashes on for about 1 second while the car is running. It's always done this. I figured something was flakey with the plugs or the relay, but it didn't seem to hurt anything. My theory is that when the plugs fire, they tax the alternator to the limit and that's what's blowing alternators. What do you guys think of this theory? Any help would be greatly appreciated.

Kip Amore
-thumbing a ride-

I assume that you have tested your charging system with a voltmeter, and even better an ammeter, to tell you if you are, or are not, charging.

I also assume that you tested all of your alternators and the wiring.

When the glow plugs 'fire' they do draw a lot of currrent, but that alone cannot damage your alternator, merely make it work hard. Unless it's a dead short, the alternator will produce full output and just stop producing more.

If the alternator does not have enough capacity to power the glow plugs or whatever electrical load is on, the rest of the power comes from the battery.

If the battery, alternator, regulator and wiring are all good, it is possible that you have a current draw while the car is switched off, such as a trunk light that doesn't shut off, or some other 'sneak' circuit that is supposed to be off, and that is draining your battery when the engine is off.

Best Regards,
Jim

Just to make sure, you might want to check to see if the grounding wire from the engine is bolted securely to the body. It is a braided cable that comes from the engine to the body. It is located near the firewall, between the engine, and the brake booster.

hope this helps

__________________
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1981 240D/297K/4-spd/OM617 (mine)
1982 240D/241K/4-spd (wife's)
1979 240D/291K/4-spd/OM617 (father-in-law's)
1983 300DT/240K/4-spd (brother-in-law's)
1985 300DT/???K/5-spd Intercooler conversion (brother-in-law's)
1985 280TE/160K/5-spd (father-in-law's)
1963 UNIMOG (brother-in-law's)

Check for voltage on the glow plugs when they should be off. If so, you will never get the battery to stay charged when you use the headlights, the total draw is more than the battery puts out (until, that is, the glow plugs burn out, anyway).

If it stays on, replace the relay.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

#A. Glow plug relay bad, causing a draw after shutdown.
#B. Possible shorted alternator.
#C. A current draw while the car is switched off will kill the battery every time.

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The fact that you have purchased three alternators within the past four months needs some investigation. Where were these purchased from and was it possible for the seller to confirm that the alternator was not functional when it was returned? Are you quite sure that the alternator has failed each time? Is is possible that the voltage regulator has failed and the
alternator(s) are still functional?

The likelihood of three bad alternators within four months is remote. It is far more likely that you have a problem with the regulator(s) and/or a problem with the grounds. As was previously stated, follow the cable from the battery to the grounding point and be absolutely sure that there is no corrosion there.

Do you have charging data when each of these alternator/regulator combos was installed? Is this data within acceptable limits (13.5V above 2000 rpm)?

I don't have an ammeter, but I test the alternators by measuring voltage across the battery terminals. Not charging =10.5-11 volts. New alternator and new voltage regulator = 13.4-14.1 volts, and it goes up with RPM. I also test by starting the car and removing the positive battery cable. Lights and wipers off, not charging. Lights and wipers stay working, charging.

I didn't test the body/engine grounds because I assumed them to be working. Wouldn't the car have all kinds of wierd electrical symptoms with bad grounds, charging system aside? A $5 battery ground and an auxillary engine ground couldn't hurt it, so I'll do that next.

When the charging system dies, I put the Diehard on a charge overnight and it takes it and stores it as it should. I'm pretty ruled out on the battery itself.

Where is the glow plug relay and how I can test it armed with my voltmeter?

Thanks a million guys,
Kip Amore

I have always heard that removing the battery while the car is running - on an alternator system (not the really old generator cars) - will destroy the voltage regulator. Not sure if its a transient that gets it or an overvoltage condition or what - but I would discontinue that test where you pull off a battery cable while the car is running.

Glow plug relay is on the driver's side fender under the hood, a bit towards the front of the car from the middle of the wheel. It has a cover over the socket and plug connectors. If you are getting a battery drain from a glow plug relay problem, you could disconnect the glow plugs connector after startup and make your drive. This would get old after a while, but might serve as a temporary workaround.

Ken300D

__________________
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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

by pulling the battery cable with the vehicle running.

The problem with the car is not that the battery drains, but that it isn't charging to begin with. What is blowing out the alternators (or voltage regulators or both)? What can cause this?

In other cars, I'd say "voltage spike" or "worn brushes" or simply replace it and forget about it. With this car I've replaced it but it's still blowing out? Suggestions?

Kip Amore
-stumped-

Is there any way to check the voltage regulator. It's looks like a single transistor, which means I should be able to read a .7volt drop across 2 legs, but not all three. Been a while since basic electronics. Any other methods would be appreciated.

Kip Amore

A bad field wire will kill an alternator.
Run a new field wire, easy and cheap.
Run an auxiliary ground from the block to the battery.
Check starter solenoid for loose connections, and replace the solenoid if needed, a loose and arcing cable will surge the alternator hard.

In the plug on the back of the alternator there are 3 wires. I assume the biggest one is the one that goes to the solenoid. Is that the field? Thanks,
Kip Amore

What year is your 240D?

The field is a small wire.

If the pigtail to the alternator is in rough condition, that could be your problem.

Please do not check an alternator by removing the battery from the circuit, there is a reason there is a warning not to do this -- blown diodes almost always result because they cannot withstand 20+ volts when the regulator loses control of the charging circuit from no reference voltage. This can also cook the regulator instantly, so you will then get no current or voltage at all.=.

I sincerely doubt you have gotten three bad alternators in a row. Please take the alternator to a parts store or repair shop and verify output before proceeding.

Once you know you have a good one, make SURE it is actually connected when installed. Corroded connections in the three wire plug or a missing output wire (or misplaced) so you never connect to the positive battery post will result in a "dead" alternator because it has not field current.

And, I will repeat, you MUST verify that the glow plugs aren't staying on. They draw more than enough current to prevent battery charging (on the order of 40 A on a four cylinder engine while the alternator can only produce 35 or so) and the battery will slowly (or quickly at night) go dead. Easy to check with a voltmeter, you should have 0V on the glow plugs with the engine running. If you have 12V, get a new relay, the old one is bad. If the glow plug light flashes once in a while, it may be cycling on and off because there are fragments of contact floating around and shorting things out.

Bad glow plug relay will be very hard on the alternator, the aren't really meant to run a full output continuously!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!