Diesel Engine basic math
 

According to my simple math, my 1985 300D has over 173,000,000 (that's million) power strokes under it's belt!

Here's my simple math:

Let's say the vehicle averaged 70 mph (a stretch I realize for us city driving types, but play along). At 70 mph, it would take 1928 hours to go the distance on my Benz (135,000 miles)

If my engine is spinning at 3000 rpm, (which is pretty close for 70 mph), it would be turning at 180,000 revolutions/hour.

In 1928 hours of driving, the engine would have made 347,000,000 (that's million for us simple types)

Finally, a four cycle diesel engine has one "power stroke" for every two revolutions of the crankshaft. Consequently, my engine has experienced 173,500,000 "power strokes" in it's 21 year life.

The "true" number of power strokes on my vehicle is greater than 173.5 million since it has not likely averaged 70 mph!

Why am I impressed? I just changed the oil on my 85 and could not detect any noticable cosumption after 4000 miles. I salute the Benz engine designers!

And what else do you do for fun.....???
 

G'mornin',

My '85 300D does not consume any noticible amounts of oil either, with 131,400 miles......

In another post here I noted that it did consume about 1/16" oil in 3000 miles.....but I began with the sump slightly overfilled, about 1/16".....all of my MB literature says that this engine holds 8 liters.....and a 1 Gallon Oil Jug contains 3.78xx liters.....when I change oil and filter, and drain all when hot, including opening/cleaning the filter canister.....replacing filter and button up filter canister.....letting oil drain until all signs of dripping stop....and add 2 Gallons of oil (7.56 liter).....run engine until warm, looking for leakage, etc......it still comes to a touch above the upper dipstick mark (hourglass)....I have the proper dipstick "ochre".... so my engine is taking about .5 liter less than it is supposed to......been wondering if I should vent the filter canister as engine runs.....anyone ever consider that there may be an air bubble in there??

I worry about the small ***** also....:D
SB

Your math is a little faulty. Actually, not your math, but the asuumptions.

Vehicle speed does not matter. In top gear the engine will turn as many revs per mile at 30mph as at 80 mph--except of course for torque converter slippage, but this shouldn't amount to more than 1-2%. The engine will turn more revs per mile in the lower gears, but unless all your driving is done locked in 2nd or 3rd, it is probably safe to assume that the differences will be small. All the errors will tend to reslt in your engine having more power strokes, and so the calculated result will be on the conservative side.

The easiest way to approximate the engine revs per mile is to look at your tach---How many revs does it indicate at 60 mph? The reason this is important is becasue, at 60 mph, you are running 1 mile per minute. You can then observe the relationship of rpm to miles---accepting, of course, that your tach is indicating accurately the rpm ( doubtful). If, for instance the tach indicate 3000 rpm at 60 mph, you can see that with your tires and rear end ration the engine turns 3000 rev/ mile. Multiply that by the number of miles and you will see the minimum revs your engine has turned to acculmulate that mileage. Divide in half to obtain the number of power strokes, or injector cycles.
You can also calculate using the loaded tire radius ( center of the drive axle to the ground) to obtain the circumference. Using that and the rear axle ration should yield similar results.

That seems to be normal, mine will take about 7.5 quarts after I let it drain for an extended amount of time with a hot engine. I assume there is some oil in the system that does not completely drain out, and I really doubt there is an air bubble left in the filter housing. It's not a good idea to overfill these engines, most people try to keep the oil level at the midpoint between the two dipstick marks. It's also best to check the oil level after it's been sitting for a while (overnight is good) to avoid getting in artificially low reading.

My train o' thought.....
 

I generally check oil before starting, usually after vehicle has been sitting idle for a day or more.....so therefore I assume that all of the oil that's gonna drain to the sump..has.....

If all oil is in sump...then if oil is at the upper marks....when engine is at rest...
Then, when engine is running, some of that oil will be pumped up into various oil passages and galleries that had drained down.....
Thus.....lowering level to somewhere in the midpoint of the high and low marks....when engine is operating...

Still, I wanna know why I cannot add the entire lube charge after oil/filter change...
Last Oil change, I was measuring the oil that I had drained out...but accidentally spilled some...invalidating that test....will do again next oil change.....:scholar:

SB

Mine has six power strokes per two revolutions of the crank.