On page 5 of this Harley white paper explains why your synthetic leaks occur.


It also gives some background on engine oils.


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Attached Files

Oil%20and%20the%20Harley%20Davidson%20motorcycle.pdf (128.0 KB, 708 views)

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1983 123.133 California
- GreaseCar Veg System

The idea that I'm pointing here is that 3,000 mile oil changes are bad for a motor and keeping it as long as you can will provide a benefit. Even though these links are for gassers, the theory behind it is the same for diesels.
Soot over 2% should be a concern. Roy stated earlier, at 9,000 miles, his worst soot load is at 1.5%. Depending on the TBN, this oil still has the potential to go further. But in the end, Roy has his change interval spot on where I think it should be without doing any UOA. Between 8,000-10,000 miles


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1983 123.133 California
- GreaseCar Veg System

Isn't science fun! We have some research papers indicating that increased soot loading increases wear rates in diesel oils, and we have other research papers indicating that wear rates decrease the older the oil is (in gassers). So in review... don't change your oil frequently, and don't change your oil infrequently.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

And the reason has nothing to do with gunk, which was my point to begin with.

Actually the best way to do it is not to change it blindly, but to have your oil analyzed by a reputable lab and run it at an interval deemed safe by the report if you are going to run it past the factory recommendations.




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1983 123.133 California
- GreaseCar Veg System

I wonder if the apparent reduction in wear material accumulation over time is not, in fact, a reflection of the oil's inability to maintain said material in suspension.

I don't think that is the case. I could be wrong about this, but this is my understanding of how the oil functions through reading various articles around the net.
Motor oil is produced with an additive package that bonds to the moving parts through the high pressure contact of the said parts. These additives account for like 3% of the volume of engine oil, but produce 90% of the engine's oil protection. With only 3% of volume, these additives need to be continuosly circulated to start bonding to the engine.
Here is an article on bob's the oil guys website about how one additive works, which is similar to the other types.

Moly Basics - Bob is the Oil Guy

When you change oil often, you introduce an initial cleansing detergent. This detergent attacks and cleans out all contaminants from the previous fill. Though it does a great job of cleaning, the drawback is it also cleans off the existing additive bond and prevents the new additives from forming their bond to the moving parts until the detergent cycle is used up during the first 1000 or 2000 miles. This is why when doing an oil analysis, several UOA's has been posted in various forums show the engine oil's wear rate is actually higher at 3,000 miles, then it is at 7,500 mile and at 10,000 miles. By keeping the engine oil in there longer, the detergent cycle is reduce and the additives get a chance to bond longer which leads to less wear on the engine plus with the added benefit of saving a lot of resources and money.


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1983 123.133 California
- GreaseCar Veg System

That is exactly my point. The oil analysis appears to give a false indication of when the wear is actually occurring. The increased dispersant capacity of the fresh oil is giving the impression of "new" wear, when, if fact, the wear particles are remnants of the previous oil cycle. The old oil was just not able to keep the wear particles in suspension.

Your point of residual metals of the previous fill might be valid. I do believe the cleansing refers mostly to removal of organic contaminants like acid, soot, water, etc. than the non-organic contaminants like wear metals. But I would think the lab would be able to trend and identify when the oil becomes saturated and loses it's ability to hold the wear metals. Also, you should be able to tell with a decrease in count of the additives magnesium and calcium that the oil no longer has the ability to remove, hold and suspend the contaminants which would lead to residuals left behind during an oil change.
I would also have to consider the SAE studies that I pointed to earlier to holding a lot if weight in this subject. It is one thing to look at an oil sample, but to get a better point of view, look at the actual parts in questioned for actual wear rates.


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1983 123.133 California
- GreaseCar Veg System

I'm willing to consider evidence showing some properties of oil are improved with age. I'd love to see the actual SAE papers referenced previously. I also think it's fair to claim too frequent oil changes are costly and unnecessary if you can back it up with evidence. But I wonder if extrapolating the test results to claim that too frequent changes are harmful is correct. I'd be very interested in data showing an engine failed prematurely due to too frequent oil changes.

FWIW our fleet vehicles regularly see 300k plus miles on original engines, both diesel and gas, with 3k mile oil changes. It's the bodies, not the engines, that usually take them out of service. If the 3k mile oil drain intervals were detrimental I'd expect to see differences between the bulk of the fleet and our three '04 Sprinters which have drain intervals ranging from 7k to 10k miles depending on oil used.

The science has proven 3k mile oil drain intervals are not detrimental, just environmentally and economically wasteful.

I know many antique/classic vehicle owners still follow the three month calendar oil service = the engine may run 5-15 hours on each oil change, with a much needed rebuild every 10-15 years.
It is debatable whether the lack of running or the excessive oil change do more to cause the required rebuild.


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