Oxidative Stability - Benchmarking Performance Over Extended Drains

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5,785
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Dixie
Even the best - shear stable - PAO and/or Ester based synthetics will thicken very slowly due to oxidation/evaporation, over the course of an extended drain interval of > 15,000 miles. The best performance I've seen is a 2% increase in viscosity for every 1000 miles; starting at the point when the oil has been in use for 10,000 miles. So you can roughly expect this type of behavior, if you track viscosity as a function of miles: Miles on sample ....Viscosity Increase @ 100C/210F: 10,000...viscosity unchanged or slightly thinner 15,000 ...+10% 20,000...+20% 25,000...+30% 30,000...+40% 35,000...+50% For example, if you run the Series 2000 formulation for 35k miles, it will thicken up by approx 50% at both low and high temps, under ideal conditions. At subzero temps, the "CCS" viscosity will increase from a 0wt to a 5wt. The high temp viscosity @ 100C will normally end up in the 15-18 Centistoke range. In laymans terms, the viscosity will increase from an SAE 0w-30 to a 5w-40, or "thin" 5w-50 - either of which is perfectly acceptable in terms of protection and performance. The key to maintaining excellent wear protection over very long drain intervals is to make sure the oil still flows well on startup/warmup, even in temps well below 0F. Allowing the oil to very slowly thicken by a grade at operating temp will cause fuel efficiency to drop by 1%-3% towards the latter part of the drain interval, but won't cause any function problems. Those of you who follow the European oil scene may have noted that many of the new long drain, ACEA "A5/B5" and VW 503/506 spec oils are SAE 0w-30 grades. Now you know the reasoning that went into that viscosity selection, particularly for gas engines. The popular TDI diesel engines produce much less oxidative thickening of the oil, however you also have soot related thickening to contend with in those applications. Tooslick www.lubedealer.com/Dixie_Synthetics [ November 17, 2003, 09:21 AM: Message edited by: TooSlick ]
 

Patman

Staff member
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Oakville, Ontario
You have to wonder though, why even bother taking the oil out to 25-35,000 miles? I know it's foolish to do 3000 mile intervals with synthetics, since it's not cost effective, but you have to reach some point where you say to yourself "why am I extending the interval so far when the oil is no longer anywhere near as effective as new?" It seems to me that if you really want to do extended intervals, then going to 10-15k is still going to get you good value for your synthetic oil dollar, while not taking things "too far" If someone is doing 25,000 miles per year, what's the difference if they do two oil changes per year instead of one? They aren't spending that much more money, or spending that much extra time doing the work, but in the long run they are probably much better off. My two cents...
 
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34,038
Location
Southern NJ
quote:
You have to wonder though, why even bother taking the oil out to 25-35,000 miles?
Agree. You spend thousands of $'s on cars and oil at most will run you $7qt, and that is for a high quality syn lube. Extending drains that far is insane IMO. I drive hard and wouldnt take any oil past 10k miles. If you drive easy, then maybe yearly oil changes I'd try but otherwise it's not worth it. I think peoples priorities are backwards. Saving money on oil changes is the most ridiculous thing I can think of when talkning about cars and maintenance. Oil is a fraction of what the car costs and if you want to save money, buy a beater or a Toyota Echo and save money on gas, NOT engine oil. [ November 17, 2003, 01:29 PM: Message edited by: buster ]
 
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Even at 1k a week, I still wouldn't go that far. I'd probably eat the savings benefits from buying two bottles of Rx down the road.
 

TooSlick

Thread starter
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5,785
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Dixie
This post was strictly informational .... I've settled in on 20k/1 year drains for my personal vehicles, unless I am specifically overtesting some new oil formulation. I'll do a filter change and topoff at the six month point. The best candidates to achieve super long change intervals are 4 cylinder, non-turbocharged engines, with modest power levels and a large sump. OCI = (C*)(mpg)(sump in qts)(cubic inches/hp) Where C* is an empirically derived constant.... Gas guzzling V-8's and high performance engines have to run significantly shorter change intervals.
 

Patman

Staff member
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Oakville, Ontario
quote:
Originally posted by TooSlick: This post was strictly informational ....
I do realize that, and I'm sorry for taking the thread off course. Info like this is definitely appreciated. [Coffee]
 
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1,533
Location
Ephraim
quote:
Originally posted by TooSlick: Allowing the oil to very slowly thicken by a grade at operating temp will cause fuel efficiency to drop by 1%-3% towards the latter part of the drain interval, but won't cause any function problems.
Maybe more, hey, but I agree. and when you are thinking you are getting close, all you have to really do is watch the fuel as the last clue to change. Course like today where it flooded here in Houston, I got ZAPPED TWICE in WATER running rough IDLE and Throwing a Check Engine Light, Idle in parking lot for SEVERAL HOURS, that would throw my numbers off a bit.
 
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2,444
Location
Indiana
quote:
Originally posted by TooSlick: OCI = (C*)(mpg)(sump in qts)(cubic inches/hp) Where C* is an empirically derived constant.... [/QB]
Great info Too Slick. Does "C" vary across cars or is this a stable number? If it varies, what are the C's for VAG 1.8T's and Volvo 2.3, five cylinder turbos? Thanks
 
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