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1985 300SD - electrical issues (soliciting suggestions)

I recently acquired a 1995 300SD Turbo as a secondary vehicle for long road trips - I was looking for something a bit more appropriate for business trips than my well-worn 1995 Ford Ranger. I wanted something presentable, comfortable, and economical, so I think I got what I'm looking for. However, I recognize already that I have some maintenance work to do before the vehicle is reliable enough to be driven 400-500 miles away from home. There are some suspension issues I need to take care of, but my main concerns have to do with the electrical system, primarily gradual discharges that keep the car from starting. I'm trying not to be a complete clueless newbie, so I have done some research and learned about the blown fuses, blower fan problems, weak alternators, and trunk lights that stay on when the lid is closed. I'm also carrying around a multimeter and taking notes when I encounter problems.

Here's what I have noticed so far:

(1) I am noticing gradual discharge when I operate the vehicle at night - not so much of a problem during the day. The combination of headlights and heater blower seem to cause the most trouble (fuse #16 blows from time to time, which I believe is the heater fan). The battery light comes on ever so dimly at idle as well. I did a static test running the car in idle with a fully charged battery (12.3 V) and noticed that the heater was responsible for an 0.3V drop and the headlights for an 0.5V drop - how significant this is I am not sure.

(2) I get intermittent "clicking" sounds from inside the dash (sometimes near the steering column, sometimes near the heater console) when the system starts slowly discharging.

(3) The battery never really dies, or even comes close to it - the clock keeps running, and even the headlights will come on moderately bright (I do lose the radio presets, however). I have checked the battery voltage, and found that it the starter turns slowly below about 11.5 volts, and simply clicks once and does nothing below about 10 volts.

(4) My (diesel) fuel gauge seems to migrate quite a bit, even when accounting for changes in level between going uphill and downhill. However, when I get down to "bingo fuel" (less than a gallon), the fuel low light will extinguish and the fuel gauge will go back UP to about 3/4 of a tank.

(5) My glow plug lights no longer come on. I haven't established whether the glow plugs are indeed bad or whether I just have a burned-out light, but the vehicle still starts in the morning (temperature usually 8-12 C, not too cold).

(6) Issues attributable to other problems, such as vacuum leaks (engine slow to shut down, acceleration even more gutless than expected) have been pretty much resolved.

Any suggestions from experienced individuals in this area would be greatly appreciated. Thanks in advance.

Stan de SD

1985 Mercedes 300SD (293K)
Reply to
Stan de SD
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Correction - 1985 300SD, not 1995. My goof, Sorry.

Reply to
Stan de SD

(1) & (3) IMHO you need to determine if the alternator and its regulator are generating the power to the battery needed to support the car's electrical needs. You ought to remove each fuse sequentially and test the draw across its circuit to determine where the electrical drain is (other than the clock). Could be trunk light, radio antenna etc.

(4) Erratic fuel gauge may be due to the sender unit being dirty and sticking. You might try a "cheat" solution to this by adding a gallon, not more, of gasoline to the fuel. The gasoline will kill any algae in the tank and dissolve any deposits that may be causing the fuel gauge to be erratic. The gasoline will cause some loss of power and a noisy idle but otherwise will be benign.

(5) The glow plugs are working (for sure) if the engine starts.

(6) Acceleration is quite affected by the adjustment of the throttle linkage. Also, whether the "banjo fitting" on the aft end of the intake manifold is clear and the rubber hose connections on that line at the switchover valve (on left side) are tight.

Good luck.

Reply to
T.G. Lambach

"Stan de SD" wrote in news:FIEOb.17833$ snipped-for-privacy@newsread1.news.pas.earthlink.net:

First i would check the stator (pick-up). It's mounted to the back of the alternator.

Remove and inspect it. If it is relatively short (1-inch), you need a new one.

A healthy one is typically 2+inchs.

Reply to
George Mann

You referring to checking current while the system is running, or voltage and/or resistance when the system is off?

I want to clarify that you're talking about adding gasoline to a diesel engine, right? If so, how much diesel should be in there; a full tank? That would be about a 16:1 ratio...

Thanks, TG. :O)

Reply to
Stan de SD

(1) & (3) Engine shut down, everything OFF - check the current draw across each fuse by removing the fuse and checking the (now open) circuit for current draw with a multimeter

(4) Suggest a half tank or more of diesel plus ONE gallon of LOWEST octane gasoline. The engine will be a bit flat and a bit noisier than normal. One CAN run these old engines on regular gasoline if that's all that's available - emergency only.

Owners used to dilute diesel with some gasoline to prevent cold weather gelling - no longer needed as Diesel #1 is sold in coldest weather areas

- contains kerosene.

Reply to
T.G. Lambach

(4) Remember, the purpose of adding some gasoline to your car's fuel is as a solvent to dissolve any deposit(s) that may be on the fuel gauge. A cheap way to clear a possible problem on the gauge.

If it doesn't help then the gauge needs to be removed and probably replaced for after 300K miles it may well be at the end of its useful life.

Alternatively, you could just refill the tank every 300 miles and the car would never run out of fuel.

Reply to
T.G. Lambach

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