My new 1983 300D has a rectangular rubber patch on the bottom of the oil pan. Anyone heard of this, or is it a repair by previous owner?

Also the alternator puts out about 13 volts when engine is revved. Seems inadequate. What to look for?

Thanks!

Not sure about the oil pan, but the regulator on the alternator could be dying. Depending on the situation it's usually less headache to just change the whole alternator out these days

The battery must be fully charged to test charging system voltage. A sticking glow plug relay can cause this, unplug it and recheck the voltage.

The voltage regulator is on the back of the alternator and is held in by two screws, not too bad to change as the alternator and even the belt stay in place. If the commutator rings are tore up replace the alternator if they are ok I'd throw a VR at it.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

What Sugar said.

I also had a issue where I used a battery that had terminals in a different place, and I had to make a longer native ground to chassis cable, and I got close to a one volt raise in charging voltage.

Like a year later when I removed my starter, I tool a good look at the positive cable and found that were the cable was inserted into the clamp was corroded. I cut a slot in the clamp pulled the cable out and cleaned both in baking soda in water getting rid of all of the corrosion.

I put the cable back in and got my propane torch and filled that cavity in the clap with the cable with solder and gained almost another charging volt.

With those 2 things I went from the minimum of 13.3 volts too 14.5 volts.

If you are unsure, remove the alternator and have it tested for free in an auto parts store or 2.

Another problematic area is inside of the pistic alternator connector. If your connector looks like the one in the picture you can carefully take it apart.

It is not unusual for the crimped-on connectors to be corroded.

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84 300D, 82 Volvo 244Gl Diesel

The rubber part of one of these oil pan heaters maybe? I have one on my 300D as well as every diesel and most of my gas engines. Really helps get your cranking speed up in Canadian temperatures, even with a block heater.

I will second the corrosion theory, corrosion is an absolute curse for auto electrics. The voltages are low already, it's easy to lose a few more volts to a bad clamp or connection.

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1993 300D 2.5L Turbo

Something my older family member told me when I was a kid. He said if you peeled back the insulation on the positive cable you would find corrosion.

When I removed the starter, I also eventually removed the positive cable and cut and peeled back the insulation. All of that white looking stuff on the wire in the picture is corrosion.

Baking soda in water neutralize the acidity and after that the cable looked pretty good except for where the cable went into the clamp.

I decided not to buy another cable and I cut a slot where the red line is on the cable and spread it out and pulled out the cable and did the baking soda water thing and the same with the cable till it was all nice and clean.

I assembled it and squeezed the slotted part of the clamp over the cable, and I filled the whole thing in with Solder. After that it was just fixing the cable insulation.

What was surprising is that the thickness of the copper part of the cable is only 1/4 of an inch. And that is the stock cable that came with the car.

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84 300D, 82 Volvo 244Gl Diesel

Someone may have patched a hole with a rubber tire patch? If so I'd replace the lower pan or have it patched with steel welded in.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Thanks for all these suggestions! I will look for bad connections. The fact that the alternator is putting out a little extra voltage over the basic 12.6 suggests it is not completely dead. I'm hoping that the rubber thing on the oil pan isn't hiding a leak, 'cuz i just changed the oil.

Also make sure the glow plugs aren't pulling voltage. They of course shouldn't be in the heat but AutoZoo's machine condemned the alternator incorrectly because of the glow. I knew that was wrong.

I went through a couple of Bosch voltage regulators before finding one that worked. That was strange because they just bolt in so there isn't much room to do it wrong.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

I tightened the lugs on the connector that goes into the back of the alternator, and cleaned them with electrical contact cleaner, and it made no difference.

The major ground connections appear solid, and the car starts easily. I would think if there were corrosion there, the starter would be sluggish. The voltage goes up to 13.0 when the engine is revved really fast.

The battery light glows dimly at idle, but gets quite bright at high revs.

I couldn't get the voltage regulator off due to awkward location but will try again with a phillips bit on the 3/8 ratchet.

The car has 272,000 miles, but don't know if the alternator was replaced. It has a sticker on it that says: Bosch AL 117X; smaller numbers below are 095 88915 A3162 Premium. Is this original, or a replacement? Hoping i can get the alternator out w/o removing all those belts and the fan.

BTW, the rubber thing DOES have wires attached, so it is a Canadian style pan heater. Happy belated Canada Day, Evranch!

Glad to hear the rubber thing may even be of use, depending where you live! They are honestly great on even a chilly day. Saves a lot of work for your battery.

Gives me a good laugh to hear it referred to as a Canadian style heater because here in Canada... they are often marketed as "Nordic style" complete with burly Norseman graphics!

There's always someone out there whose winter sounds worse than yours.

Contact cleaner on an old car is often not good enough. I pull the lugs off the post and polish both them and the washers/nuts with emery paper until they shine like copper again. Then coat with an anti-corrosion agent like "Penetrox" and torque the nuts as much as possible without stripping something (careful!). Especially on a high current diesel starter this can make the difference between weak cranking and hot terminal posts, and a good snappy start.

This is odd and almost certainly indicative of a fault, but I can't think of what at the moment. That light is hooked to ignition ON, and passes current from the battery to excite the alternator. It then goes out when the alternator begins to generate power and "kicks back" 14v.

It should be bright before starting the car, then turn off unless the alternator has failed and cannot generate (brushes, diodes, snapped belt etc) It should never be dim, and it should certainly not get brighter with increased RPM as that implies the alternator is generating less power with more speed.

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1993 300D 2.5L Turbo