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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. Quote:
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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: Quote:
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.
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'84 760 D24T/M46 '86 Isuzu Trooper Turbo Diesel '01 VW Golf TDI |
#12
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well oiled
hi again
there are some interesting points here, perhaps i can add some more. I dont think that anyone is questioning your findings of your oil analysis carioqv, but perhaps your application of them. The trouble is that your results are unique to your own car and operating conditions and yet you appear to apply them carte blanche to all. There are other factors involved such as operating in dust laden environments, being laid up under damp conditions causing water absorbtion, high fuel sulphur levels, driving styles etc. These will contaminate the oil. As you correctly state, the oil filter cant do much about normal engine wear particles, but the above conditions will have an adverse affect on its service life. ( incidently autodata suggests 10k for an oil service on a '93 volvo 940 D24T ) I do around a dozen oil changes a week in the course of my business and cannot recommend anything other than the manufacturers service schedule - this is also the stance of all the leading brands as far as i know, the reason for this is that without a proper oil analysis survey for each individual car it would effectively be guesswork based on someone elses individual findings ( and proffesional suicide on my part ) Dont get me wrong mate, i admire your enthusiasm and diligance in this subject, not to mention the interest it brings to the forum, but few people have the time, inclination or ability to carry out these tests and these are the people that the manufacturers must protect. If in doubt folks, stick to the book and change that oil (along with the rest of the service schedule ) and if you think that your poor car is suffering from the abuse your giving it , follow your gut feelings and just do it when you think it needs it. That may not be the perfect solution but it will always be the safest. Brian |
#13
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ps. are you sure that valve takes 40 tonnes per square inch to open ?
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However: 1) I think the D24/D24T may be an exception, since not using Group IV synthetic seems to result in stuck rings, and rapid engine wear (unlike most diesel engines such as Mercedes which seem to experience only about twice the metallic wear rate on non-synthetic). Since our engines require nearly 2 gallons of oil, extended drain intervals with synthetic are really the only economical option for us. The fact that our engine manufacturer (VW) actually specifies extended drain intervals on synthetic for the TDI (a newer evolution of the same engine family) also lends credibility to this approach. 2) In some cases people have bought into marketing hype (from companies selling oil) that 3,000 mile changes will improve engine longevity, so they're actually using shorter intervals than their manufacturer recommends. They probably should follow the factory interval instead, since there is some evidence that needlessly shortening the interval could accelerate, rather than reduce wear.
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'84 760 D24T/M46 '86 Isuzu Trooper Turbo Diesel '01 VW Golf TDI |
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I read a few different tests on oil contamination levels, and I saw how they were plotting results on the graph and showing the trend from new oil and the bigger rise in the first 3k miles of wear particles. However all the ones I saw were started with the contamination level of zero. That isn't accurate, the oil is contaminated as soon as you start it thanks to oil hang up/film, plus the extra half quart of oil left in the engine in oil passages, the pump, etc.. I noticed it was said in more than one study what a difference the fresh filter makes along with the fresh oil top off in changing the oils characteristics and helping extend the oils life. I think the same can be said for the instant quart of dirty oil that is at full contamination that was left in the engine mixing in with the new oil. I would be interested to see a test in which the "clean" oil sample is taken after the first 20 or 25 miles of use after everything is mixed in...
As for my engine's soot load... I think 5k mile changes are what I'm sticking with. I run my car harder than many probably think, and as immature as it is, I still love blasting smoke on people that tailgate me, annoying ricer cars, and sometimes just for fun. I'm 27 going on 12 what can I say! Jason
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Back again with a '84 760 GLE D24T/ZF SOLD but not forgotten! 1984 760 Sedan, built D24Tic/ T-5 swapped My engine build: http://www.d24t.com/showthread.php?t...t=engine+build T-5 swap: http://d24t.com/showthread.php?399-W...to-quot-w-pics! |
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All I'm saying is that there's no way to know what your soot levels are without an oil analysis. If they're much lower than you think at 5k, then you could save a ton of money by extending your interval, and if they're much higher than you could potentially decrease wear by further shortening the interval, raising your boost or otherwise leaning out the motor. I'd put my money on the former (even running it hard and rich I'd bet you soot levels are low at 5k).
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'84 760 D24T/M46 '86 Isuzu Trooper Turbo Diesel '01 VW Golf TDI |
#17
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just one caviat modern iol burners can have comp ratios as low as 16 to 1 so they aint going to mash up the lube like our 23 to 1 rattlers , volvo use 0/30 in cars with 18000 mile intervals but warn the oil can go bad much past 20000 (fully synth) I had to replace the motor in one (d5) the guy had run 28000 on the same oil & it had turned to tar. they say when the modern type oil goes bad it does it fast , but change it when ever your happy for your own preference so long as u check it regular , if it looks shit it probly is d24`s started out at 5k services & later went to 10k so if your in that ball park most people will be happy lol.
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