You are definitely right I was mistaken and I feel stupid for saying what I did about the oil light. I was thinking it was like some of the really new cars that actually tell you when it needs to be changed. This car only tells when it's low so that is useless to me. Thank you for pointing that out. Still yet the oil is pretty black so obviously it's broken down and it needs to be changed. All I'm saying is with a 26 or so gallon tank and 25 mpg I should be able to drive 45-50 miles and no matter WHERE the needle is on the gauge it shouldn't hardly move. That's a BIG tank. My 91 Mitsubishi Mirage has a 13 gallon fuel tank and I can drive that distance and the gauge hardly even moves and that's half the size of the tank on this car. You can't honestly tell me that driving 45-50 miles on an 1/8 of a tank there isn't something wrong. I've driven so many different types of vehicles and I have always been pretty damn good at guessing the mileage with such measures I am using. Not to mention every vehicle I have ever owned the needle has gone slower on the top half of the tank then it has on the bottom half. My needle was almost on the 3/4 mark when I started the drive and ended 1/8 of a tank lower then that when I was finished. Then I drove another 40 miles and it was on half a tank. So 1/4 of the top half of the tank and only gone 80-90 miles at the most? So that means if I drive another 100 miles my car will obviously be on empty. Is that really that hard to figure out?

I'm not trying to argue with anyone either I'm just saying just because you believe there is no way anything can be told by doing it this way doesn't mean that it can't be done.

All I'm saying is the mileage is extremely bad. If I can watch the needle move while I'm driving something isn't right.

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86 Mercedes 300SDL - 400k+ miles

No need to feel stupid on that one, it's not always obvious what features they've installed or haven't just by the pic on the dashboard. That said though, something you might not be familiar with on this particular engine is that there is no possible way to completely change the oil. There's always something like half a quart of oil that is retained in the oil cooler and the lines going to and from it. It doesn't drain back to the pan, and it is more trouble than it is worth by miles and miles to pull the lines off to drain the thing. And, just like a few drops of food coloring in a huge volume of water, that oil is enough to turn a fresh clean oil change black within 300 miles. Every time I change mine, it's black within a week. It's not an indication of oil quality on diesels the way it is on gas engines. They produce so much soot that the oil goes black long before it has "broken down".

That being said, there's certainly no harm in doing a feel-good oil change. Ever. It's always something the engine appreciates. But I'm just saying you have to go by mileage on these engines because there is *no* reliable way to tell visually.

You may well be right. But in my own humble opinion, unless fuel is dripping to the ground constantly, there is no physical way possible for this engine, no matter *what* malfunction, to go through fuel that fast. It is literally impossible to put that much fuel through the six cylinders that are under this particular hood, under *any* circumstances. So, I choose to believe it's probably a faulty gauge rather than a miracle-engine.

I would make this suggestion. Get a long stick like a tomato stake or a broom handle, preferably one that is clean. Broom handle's actually a good idea; it can be wiped off with a paper towel beforehand and probably not have any dirt remaining on it. Stick it in the tank to use as a level checker. I could be wrong, as you've pointed out. But I seriously suspect that if you dip your tank when it's full with the broom handle, and then drive your 1/8 of a tank in 50 miles, and dip it again, you will NOT see a 1/8 tank change on the broom handle. The tank, so you know what you're dipping, is large, virtually rectangular, and goes from side to side across the back between the back seats and the trunk. Insert it carefully so you don't bash the strainer or the fuel sending unit or anything. It's not a muzzle loader; but you shouldn't damage anything as long as you do this carefully.

Like all electrical devices, a small error can have large results. I'm believing this to be the case with your fuel sender. It's a fairly simple resistance device; the resistance increases and decreases with the fuel level (can't remember if it's linear or inverse but it's one or the other) -- and so any simple electrical problem... short... dirty contacts... any of the thousand factors that could affect electrical resistance could be acting up in your gauge. I can very very easily imagine that your fuel gauge is malfunctioning in such a way that it... it assumes the tank is much much smaller than it actually is. I'm saying it's possible, presumably, for the float on the sending unit to be at 1/2 tank and report empty to the gauge. That's why you need a visual confirmation with the stick or something similar.

My $0.02. You may be right. But I consider 1/8 of 25 gallons to be more fuel than ANY 300SDL could burn in 50 miles, even if you had your foot on the floor up an equivalent hill to Mt. Everest, burning used motor oil and transmission fluid instead of good clean diesel, with an elephant buckled into each remaining seat belt, towing a filled swimming pool. I'm not trying to argue either, but that's how ridiculous that fuel consumption figure sounds based on the known characteristics of this engine.

For the record, I always use my odometer instead of the fuel gauge, and I refill somewhere between 525 and 560 miles, for safety. According to what I can put in at that time, there's still usually a couple gallons left, but I've run out once so once bitten, twice shy.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL