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Fuels & Lubricants Discussion all about Fuels & Lubricants. synthetic oil, conventional oil, brands, change intervals, diesel grades, gelling and such debated items like that. Non TDI related postings will be moved or removed. This forum is NOT for the discussion of biodiesel and other alternative fuels.

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Old October 18th, 2012, 18:15   #2716
TooSlick
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Viscosity is almost never going to stay exactly the same as fresh oil. Causes of thickening include:

1) evaporation of lighter fractions of the base oil and/or additives
2) oxidation and nitration - chemical reactions with O2 and NO2.
3) buildup of soot and silicon

Nothing to see here, analysis results are fine.

TS
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Old October 18th, 2012, 18:47   #2717
Ski in NC
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Quote:
Originally Posted by Bob_Fout View Post
1.5 quarts of make up oil added? 100C visco is 14.2 cSt on the spec sheet.
1.5 total qt burned. Started off full, at about 6000mi added 3/4qt. At change time it was back at add mark. So only added 3/4qt, but it burned twice that. Not going to top up at change time!
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Old October 18th, 2012, 19:05   #2718
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Ski,

Are you running the Rotella T6 in the Cummins marine engine? I'd be interested to see how it holds up under continuous heavy load. Most 5w-40's will shear under those conditions....

TS
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Old October 18th, 2012, 19:09   #2719
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Quote:
Originally Posted by Ski in NC View Post
1.5 total qt burned. Started off full, at about 6000mi added 3/4qt. At change time it was back at add mark. So only added 3/4qt, but it burned twice that. Not going to top up at change time!
OK, if you only added 0.75 quarts of new oil over the OCI, it should reflect that.
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Old October 18th, 2012, 19:27   #2720
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Quote:
Originally Posted by TooSlick View Post
Ski,

Are you running the Rotella T6 in the Cummins marine engine? I'd be interested to see how it holds up under continuous heavy load. Most 5w-40's will shear under those conditions....

TS
No, I run regular Rotella T 15-40 dino oil in that engine. On that boat it runs a very light duty cycle, cruising at 1100rpm and about 10% load. Not enough heat anywhere in the engine to justify running synthetic. Occasionally I run at 75% power and 2100rpm to blow things clean. I did an oil sample and it came out ok, but copper was high. I think the low load may get some moisture in oil and it leaches the oil cooler. Otherwise, sample ok at 300hr interval.

If fuel prices were lower, I'd cruise at 1900-2100rpm but that's about 12gph (estimated) and that's 50 bucks an hour. At 1100rpm its 2gph (verified over 8500nm).

I know the low load is not the best for the engine, but the fuel prices dictate duty cycle.

I often take oil samples on other Cummins marine engines, and none of these were using synthetic. Even at high load factors, the Cummins samples show good results unless there is an underlying issue such as sea water driven corrosion. Even dino oil holds up well.

The marine engine crowd has not adopted syn oil, except late model MAN engines, where it required. Cummins, Cat, Yanmar do not require it for warranty, even with high specific output.


Bob Fout: You are being picky. It used 1.5 qt. If I never added oil, it would be 1.5qt low and makeup would be zero!! And I think I was in the beers when I filled out the slip, so there.
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Old October 18th, 2012, 19:53   #2721
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Quote:
Originally Posted by Ski in NC View Post
Bob Fout: You are being picky. It used 1.5 qt. If I never added oil, it would be 1.5qt low and makeup would be zero!! And I think I was in the beers when I filled out the slip, so there.
I'm not being picky really. "They"/"We" really don't care how much oil was consumed, only how much "new" oil has been added during the interval, as this will skew the results. Take into account how much new oil has "contaminated" the sample and how long ago it was added.
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Old October 18th, 2012, 20:46   #2722
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Below is a recent UOA.

Details: Mobile 1 TDT, bypass filter, original cam/lifters, almost all highway commute miles, 3 oz. ZDDP added at about 10K into this interval. I burn between 5% and 20% biodiesel with no additives.

No obvious problems I can see in terms of wear. I'm interested in knowing what the boundary is with regard to interval extension and whether TBN is something I need to be getting on future UOAs. Any/all analyses and comments welcome.

Thanks!


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Old October 18th, 2012, 20:52   #2723
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Quote:
Originally Posted by Bob_Fout View Post
I'm not being picky really. "They"/"We" really don't care how much oil was consumed, only how much "new" oil has been added during the interval, as this will skew the results. Take into account how much new oil has "contaminated" the sample and how long ago it was added.
Fair enough. Dilution by new added oil would not change much regarding the numbers in this case.

My thinking with this sample makes me a bit skeptical of those engines that can go a full OCI without top up. Do they consider the oil level drop as I did, are the engines that tight, or a little BS involved??
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Old October 18th, 2012, 20:57   #2724
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Oly- That sample looks stellar. Wear metals low, insolubles low, TBN still high, dilution low. You could run that oil longer.... How much longer?? Good question. Others may have an opinion.
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Old October 18th, 2012, 21:52   #2725
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Thanks, Ski -- it's certainly encouraging!
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Old October 19th, 2012, 08:54   #2726
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Oly,

It's always tough to extrapolate test results based on one data point. However I'd certainly feel comfortable extending this batch of oil out to 20,000 miles based on the overall parameters shown here. As for the TBN limit, if you're using Blackstone labs I'd use a condemnation limit of 25% of the baseline TBN (~ 2.6 for the Mobil 1). If you're testing with other labs using the ASTM "D-4739" protocol (Oil Analyzers Inc., AVLube, etc), I'd use a lower limit of 33% of the baseline TBN.


The TBN may not be the limiting factor in how long you can run the oil. You also have to look at viscosity, soot, silicon, fuel dilution, etc.

FWIW, I don't think doping any oil with supplemental additives is advisable.

TS
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Old October 19th, 2012, 09:07   #2727
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Quote:
Originally Posted by TooSlick View Post

FWIW, I don't think doping any oil with supplemental additives is advisable.

TS
Amen to that!
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Old October 19th, 2012, 10:33   #2728
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Quote:
Originally Posted by Ski in NC View Post
Fair enough. Dilution by new added oil would not change much regarding the numbers in this case.

My thinking with this sample makes me a bit skeptical of those engines that can go a full OCI without top up. Do they consider the oil level drop as I did, are the engines that tight, or a little BS involved??
All the numbers are affected *some* by new oil. TBN, additive levels, visco etc. 15% volume isn't a lot though, and well within normal usage.

I would say 0.5 quarts is "normal" average oil used for 10K miles for most. If you fill the to max mark (this is not the hash, but the bend) at an oil change, 0.5 quarts puts you at about the middle of the hash at change-out.
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Old October 19th, 2012, 17:32   #2729
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Thanks, TooSlick and Scratcher -- I was sort of under the impression that zinc was a primary limiting factor in longevity of the interval -- perhaps not. I also understand that excess would probably not be good for the CAT but that this was't too excessive.

So do you think that the added ZDDP made no difference? Do you think my analysis would be similar had I not added the ZDDP?

Thanks for the input guys!
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Old October 19th, 2012, 17:45   #2730
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Oly,

Look at the results of your previous test. You had 1/2 as much ZDDP and the wear profile was essentially the same. You're not going to use up the ZDDP in any oil under normal conditions...

TS
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