looking for grunt !

[casioqv]

Originally Posted by Aidan

Essentially it translates as fresh clean oil causes more engine wear than dirty old oil, how can that be?

This is exactly what I'm saying- as the additive package in good quality oil "breaks in" engine wear decreases, and changing your oil more often than necessary can actually shorten engine life. It seems to contradict conventional wisdom, but it's supported by significant evidence- and is now recognized by most diesel engine manufacturers (VWs official recommendation for TDIs is 30k miles, but was reduced in the US market to 10k for psychological reasons). In my opinion, conventional wisdom is *very rarely* accurate about anything, not just this issue.

Originally Posted by Jason

I would also be interested to know how metal contamination in the oil is going to decrease over time from a higher point at the begining, as the engine is running and adding more wear particles to the oil.

Metal contamination doesn't decrease over time- the rate at which it increases (the first derivative of contaminant concentration which directly represents metallic wear rates in the engine) decreases.

Although, IF the wear rate is low enough actual contaminant concentrations can actually drop in some cases depending on the rate at which oil is burned/used and replaced.

Originally Posted by Jason

I change mine every 5k miles, though I would push it farther if it was just a stock driver.

I certainly understand your desire for caution with all of the work you put into your new motor! An oil analysis would likely show that you could go much longer without any ill effects, and would pay for itself quickly if it proved that you could safely use longer intervals. I live in a hot climate with a really mountainous terrain and much of my driving involves towing a 3,000lb sailboat. I plan to post a 15k oil analysis once I get to that point, but I won't be doing them more frequently than that.

Originally Posted by Jason

Every major diesel engine manufacturer I know of have an oil change interval recomendation, and a "severe duty" oil change recomendation, which is always shorter. I would classify my engine as severe duty since I run the crap out of it, and the fuel is turned up so soot contamination levels are higher than a stock tuned engine.

I think this has a lot to do with the engine manufacturers not wanting to require synthetic oil, and does not apply if a group IV synthetic is used. As for soot load, that's certainly easy to test for in any oil analysis. Soot won't appreciably increase wear until it reaches a certain concentration.

Originally Posted by Aidan

I am assuming this information is based upon oil analysis which determines the metallic particle content of the oil. Is there not the possability that the analysis is being "corrupted" by the fact that when you put new oil in your engine, it will very quickly pick up the residue from the old oil (which obviosly will have a fair concentration of metallic particles) and thus give an artificially high particle content reading in the early stages of the oil's life.

Your explanation doesn't make sense- because the new oil will mix with any existing oil residue almost instantly. What I'm talking about is a gradual reduction in wear rate over the first 15,000 miles or so after an oil change. Any residual contaminants can be accounted for with an initial oil analysis shortly after changing the oil.

Originally Posted by Aidan

in 33 years as a mechanic this is the first time I'm ever come across a statement suggesting new oil causes more engine wear than old oil.

This was not true until the advent of modern group IV synthetic oil technology, and still isn't true if you're not using the "right" oils.

Originally Posted by DBS404

Secondly you may expect that to fall as the new filter gradually cleans up.
lastly ( and crucially ) as the filter reaches capacity and begins to choke , oil pressure starts to beat the filter bypass valve and recirculates the oil back into your engine ......this could account for the heavy initial contamination that you found also.

Metallic wear particles from normal engine wear are far to small to be affected in any way by the filter.

Originally Posted by DBS404

Just a thought. there is no doubt that these synthetics will last for huge service intervals 18K + even, but these are for modern ecu controlled engines with common rail injection etc , not our `old` engines.

The newer engines do burn cleaner with less soot load in the oil, but even our old ones take at least 25-30k miles before they get high enough soot levels to increase engine wear, with a modern diesel rated synthetic. The main difference is better oil technology, not the new engines!

Originally Posted by DBS404

even if the oil does last 15K best change your filters at least twice by then - oil and filters are cheap compared to fuel costs for worn engines and rebuilds. cheers brian

The factory filter change recommendation for the D24T filter on non-synthetic oil is 15k miles, or every other oil change. This is a huge filter at least twice the size you'd expect on an engine like ours. If anything, the drastically reduced wear rates of synthetic oil should let you increase, rather than decrease the filter change interval.

I agree that oil and filters are cheap compared to engines, which is why I take a very conservative approach of looking at the research as an engineer and collecting my own data instead of following conventional wisdom! I have been doing it this way for 10 years, and none of my gasoline or diesel cars have had a measurable decrease in engine compression, increase in oil consumption, or measurable timing chain stretch (in Mercedes diesels) with extended drain intervals.

Now for some clarification: Here's an example of metallic wear rates over 18,000 miles using Mobil 1 in a Chevy LS1 gasoline engine (bottom 3 shaded lines). You'll find similar examples in both gas an diesel engines on car forums all over the internet if you search for threads where people post oil analysis at regular intervals during an extended drain interval.


Source: Paradise Garage Synthetic Oil Life Study

Here is a detailed explanation of the underlying mechanism, taken from a post on TDIclub.com:

STOP STOP STOP!

The ORIGINAL factory APPROVED oil change interval is 30,000 miles! YES 30,000 MILES!!

Did you comprehend that?

THE ORGINAL OIL CHANGE INTERVAL APPROVAL IS 30,000 MILES!!!

Now that I have that off my chest,

VW reduced the interval from 30,000 miles to 10,000 miles in the US market...any guesses why?

Because people like you either:
1) Can't read the owners manual
2) Don't trust the car makers
3) Can't follow directions
4) Fail to adhere to the service indicator in the car

VW does NOT want oil change intervals of less than 10,000 miles due to how the oils function in the engine, shorter intervals INCREASE WEAR, Don't argue with me about it, if you take the time to track wear rates during an oil change at 250 mile intervals you can plot the reduction and stabilization of the wear rates out beyond 25,000 miles!

Think of oil as having 2 types of wear reducing additives, the first provides protection by/thru detergancy (cleansing of internal surfaces), dispersing soot, neutralizing acids (not an issue now with ULSD), and several other types as well. These additives are generally very specific to diesel engines and must pass specific tests in VW Diesel engines.

The next type of additive is a wear additive. These protect the engine where the thickness of oil may be too thin to prevent metal to metal contact. Other additves in this type range also provide protection to the cam and lifters, engine bearings, piston wrist pins etc.

Now pay attention, the 2nd group of additives account for less than 3% of the total volume of the oil. These additives also account for 90% of the engines oil protection! These additives require heat and pressure to bond with the critical wear surfaces, but due to the low percentage of additive in the oil they require time to fully place on those surfaces by the pressures of the component they are protecting. Example, an engine at operating temperature at the point where the cam presses on the lifter generates in excess of 90,000 psi, that pressure and the heat of the engine causes the 3% portion of the 1 micron thick oil film to form a crust or sacrifical layer at the point of contact. Since only 3% of the oil contains the wear additives, it requires hundreds of thousands of passes to generate a sufficient film to stop the wear at this specific point in the engine.

Everybody is quick to make the arguement that the old oil had these additives so they are already in place, right? not quite!

Remember the first type of additive? In that 1st group you had "detergents" that cleanse the inside of the motor. These cleansers are used up very rapidly after an oil change since they attack the remaining oil that was left after the oil change. These cleansers if you will also reduce the effectiveness of the high pressure wear additives...See where this is going?

Before explaining further, after that initial period the dispersants in the oil work to prevent the adhering of the particles in the oil to any of the internal surfaces. These additives are often unique to diesel engines are also the reason why the oil looks so black so quickly, they are doing their job by preventing the soot from building up in any one place instead they are dispersed in the oil evenly throughout the oil sump which prevents sludging and other contamination related issues.

Back to the detergents and the high pressure additives, the layers of high pressure additives leftover are not being replenished after the oil change due to the cleaning process that is going on with the new oil to neutralize the remaining acids, and other contaminants in the engine. As the cleaners in the oil are used up in the first 500-1000 miles, the wear additives are able to re-generate a protective layer in the engine that stops the wear at that location.

You break down the oils life cycle like this:

Phase 1: Detergants attack the internals removing accumlated contaminants, neutralize acids and force those into suspenstion in the oil. This period of time lasts between 500-1000 miles

Phase 2: During the first 1000 miles the oils viscosity provides the majority of the wear protection by virtue of the film it creates on the surfaces. This phase generates relatively high wear rates but due to the short duration this is accepted due to the removal of contaminants that could result in long term damage to the motor. Wear rates in the period of time are generally speaking 5-10ppm per 1000 miles.

Phase 3: Detergents are now used up and the oil additives are forming their protective layers in the "extreme pressure" regions of the motor. Now the oil additives are working in conjunction with the oil film and the wear rates drop from 10ppm per 1000 miles to around 1-2ppm per 1000 miles.

Phase 4: Longterm peace! The oil is operating in a period of equilibrium, the wear additives are placed, Oil viscosity is in perfect range for the engine, Dispersants are continually working to prevent soot and other contaminants from accumulating on the surfaces and wear rates remain between 1-3ppm per 1000 miles.

Phase 5: Oil run out, the oil during this phase begins to increase in viscosity (or thin in some cases), Extreme pressure additives begin to lose effectiveness due to increased concentrations of wear particles (VW tests out to 8%, most oil changes never see in excess of 2% after 30,000 miles). This is when you begin to see a rise in the wear metal formation in the engine. Often wear metals during this phase rise to the 3-8ppm per 1000 mile range. Notice that the wear metals being generated are still LOWER than they were in the first 1000 miles?

--------------------------------------------------------------

When somebody says they are going to change the oil every 5000 miles or twice as often they are DOUBLING the number of detergent cycles and DOUBLING the number of cycles where the engine is running at it's highest wear rates!

PPM/Fe (generation of Fe in 1000 mile increments)
Short drain intervals
1K oil change
10ppm = 10ppm in 1000 miles = 10ppm/1000 miles

3K oil change
10+2+2 = 14ppm in 3000 miles = 4.6ppm/1000 miles

5K oil change
10+2+2+2+2: Change oil = 18ppm in 5000 miles = 3.6ppm/1000 miles

Long drain intervals
10K oil change
10+2+2+2+2+2+2+2+2+3 = 29 ppm in 10,000 miles = 2.9ppm/1000 miles

15K oil change
10+2+2+2+2+2+2+2+2+3+3+3+3+3+3 = 44ppm in 15,000 miles = 2.9 ppm/1000 miles

20K oil change
10+2+2+2+2+2+2+2+2+3+3+3+3+3+3+3+3+3+4+4 = 61ppm in 20,000 miles = 3.3ppm/1000 miles

When ppm of Fe per 1000 miles reaches 5-7ppm per 1000 miles you can consider the oil ready for a change...

The above is based on real world TDI oil samples.

I have personally used up to 25,000 mile oil drain intervals on my TDI and still never reached the 5-7ppm range! I changed it at that time due to soot and TBN depletion (high sulfur fuel at the time).

Anybody that tells you that short oil drain intervals are good for your motor don't know what they are talking about!

10-15k is probably the "sweet spot" for absolutely minimal wear, but 25-30k intervals are perfectly safe, and are roughly comparable to 5k mile intervals in terms of long term metallic wear rates.

I can see no reason why we can't use the 30k mile recommendation in our D24T engines- they aren't that different from the TDI in terms of design factors that affect their lubrication needs, and the oil volume in the D24 is considerably higher. Not to mention the fact that Tom Bryant uses 25k mile intervals on Mobil 1 in all of his cars and his customers cars, and reports no measurable metallic wear in the ones he's torn down after many years for other reasons.