RS4 Fuel Dilution Study (very long and geeky)
12-13-2006, 04:22 PM
#1
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RS4 Fuel Dilution Study (very long and geeky)
As some of you may know, I have been studying oil performance in the RS4 engine since Day-1, and working with Terry Dyson of Dyson Analysis ( http://www.dysonanalysis.com/ ) on the analysis and interpretation of the results. In the process, we have discovered that fuel dilution is a significant issue with this engine.
For those that are not familiar, fuel dilution refers to fuel contamination of the engine oil, thus diluting it. This dilution causes the engine to "eat" oil, causing some oils to change to a lower viscosity rapidly (also called shearing ... the factory oil shears to a 20W oil), causing increased acidity (requiring the detergent additive package to be depleted more quickly than would be nice), causing increased engine component wear, increased oil consumption, and reducing the intervals between oil changes.
Based on previous analysis which I have shared, that show fuel dilution to be an issue with my engine, I worked with Terry to design a test regimen to determine if fuel dilution is a general problem with the engine, or specific to an operating mode. The following set of tests were performed in the following order:
1) For 143 miles after oil, oil filter and air filter change, I drove predominantly (>95%) on highway with low throttle settings (never above 1/4 throttle. Afterwards I took an oil sample.
2) For 51 miles I drove 99% highway miles alternating between high throttle (>3/4 throttle) and no throttle (similar to the famous Rubberband(tm) break-in method), with absolutely no wide open throttle used (WOT). Afterwards I took a second oil sample.
3) For 50 miles I drove 99% highway miles alternating between WOT and no throttle ... which was a hell of a lot of fun ... made me quite motion sick ... with no throttle settings in between. Afterwards I took a third oil sample.
4) For 40 minutes I parked the car in the driveway and let the engine idle. Afterwards I took a fourth oil sample.
After a week and a half, the results are now in, and here are the conclusions:
Fuel dilution does happen in this engine, as determined by several methods, Flashpoint being the most sensitive, and confirmed by Infrared Spectroscopy. The results are quite interesting. For the oil I'm using, the flashpoint of Motul 8100 E-tech 0W-40 is 430 F. After 143 miles at low throttle settings, the flashpoint of the oil reduced to 365 F. After 51 additional miles at high throttle settings (no WOT) the flashpoint was lowered to 345 degrees. However, clearly the largest change occured with WOT runs, where the flashpoint dropped dramatically to 280 F. And at idle for 40 minutes it stayed at 280 C. Here's a compliation of the results:
Baseline - Motul 0W-40 - 430 F - 0% dilution
Run_1 - Low throttle - 365 F - 0.85% dilution
Run_2 - High Throttle - 345 F - 1.1% dilution
Run_3 - WOT - 280 F - 2% dilution
Run_4 - Idle - 280 F - 2% dilution
The same trend can be seen in TBN numbers. TBN (Total Base Number) is a measure of the additive package acid acid neutralization capability.
Baseline - Motul 0W-40 - TBN 10.1
Run_1 - Low throttle - TBN 9.8
Run_2 - High Throttle - TBN 8.9
Run_3 - WOT - TBN 8.8
Run_4 - Idle - TBN 8.9
As fuel dilution occurs, the additive package of the oil is reacting to counteract the acids from the fuel, causing depletion of the add package. Just like adding chemicals to a pool or hottub. If you look at the numbers, 10% of the life of the oil was depleted in < 300 miles of driving. Now, part of this driving was extreme, even for my tastes, but it does show some interesting trends.
First, fuel dilution seems to be a consequence of this engine design, and most likely a consequence of having a direct injection nozzle squirting fuel into the chamber at 1500 psi. We can see this conclusively from the Run_1 results under extremely mild driving conditions.
Second, fuel dilution is proportional to the mass of fuel injected into the chamber. The more fuel, the more dilution, and is worse at WOT where the injectors run extremely rich, as has been shown by Kimbo's dyno plots.
For those naysayers that think the problem is one of poor ring seal, blow-by, or idling, these have been eliminated by either experimental design or further analysis results. Blow-by and ring seal are discounted for several reasons. First, this engine has near zero oil consumption and has since 1800 miles. It currently has consumed 1/4 Qt over the past 7000 miles. Second, all analytical measures of additional blow-by, such as Oxidation, Nitration and Soot are extremely low or non-existent. Finally, the engine was only allowed to idle for seconds before and after each run in the test. And at idle, there is no noticable increase in fuel dilution, eliminating this as a prime cause for previous fuel dilution measurement.
(As a side note, at idle the engine does not move enough oil to allow the diluted fuel in the oil to vaporize through the crankcase ventilation system. If the engine is again run at low throttle settings on the highway, fuel dilution numbers will decrease, as the fuel vaporizes away, to the level consistent with the average engine throttle setting.)
Based on these results, I am taking steps to improve the fuel dilution performance of the engine through some additional work with Terry, following his recommendations, and additional oil analysis. Some of these are considered proprietary to Terry and his business. However, if you want to get in on the fun, I would recommend other owners to do the following:
1) For new engines, change out the factory oil right after break-in, at 1500 miles, to get rid of the contaminated oil.
2) Do not go WOT at any time during break-in, until after you get the factory oil changed out. You'll just be pumping fuel into oil which has sheared and increasing the wear exponentially.
3) Use a good Audi 502 approved oil (for now) and change it early and often as the engine continues break-in, (1500 miles, 3000 miles, 5000 miles, 7500 miles), and then at 3000-5000 mile intervals thereafter.
4) Pick your favorite oil and have it periodically analyzed to determine the state of the oil in your engine. You'll be amazed at what you can learn from a good analysis and professional reading of that analysis.
5) Go here http://www.lubecontrol.com/fuel.htm and order some FP60 as a fuel additive, follow the instructions, and use it religiously. I can't tell you why, but trust me, it's a good thing for this engine.
6) Finally, I would highly recommend that RS4 owners work with Terry Dyson (http://www.dysonanalysis.com) to have their oil sampled and analyzed, so that as a group we can further track issues with this engine. The more data we have, the more informed we will be. And, the more data Terry will have to draw upon in forming conclusions and corrective action. For $50 per sample, you get to have his recommendations for your engine, driving style, environmental conditions ... etc. And much of that information is proprietary. I am implementing his recommendations currently. (AND, as an added bonus, you'll actually learn why your particular oil works the way it does, and why FP60 fuel additive is recommended.)
For those who want to get involved and sample your oil, I recommend the Dyson Premium analysis highly. Having compared it's results to Blackstone, it is superior in all aspects. However, should you need a method to sample your oil easily, I would suggest that you pick up a sampling pump from either Blackstone or Amsoil
Oil Analysis
http://www.dysonanalysis.com/premiumkits.html
http://www.blackstone-labs.com/pump.html
http://www.amsoil.com/storefront/detail.aspx?ID=3006
FP60
Odis Beavers
Phone # 214 929 2704/2703
or
http://www.lubecontrol.com/fuel.htm
I hope that a few of you find this information useful.
Finally, by way of disclaimer, I have no financial involvement with any of these companies or services. I use them, because they are good.
For those that are not familiar, fuel dilution refers to fuel contamination of the engine oil, thus diluting it. This dilution causes the engine to "eat" oil, causing some oils to change to a lower viscosity rapidly (also called shearing ... the factory oil shears to a 20W oil), causing increased acidity (requiring the detergent additive package to be depleted more quickly than would be nice), causing increased engine component wear, increased oil consumption, and reducing the intervals between oil changes.
Based on previous analysis which I have shared, that show fuel dilution to be an issue with my engine, I worked with Terry to design a test regimen to determine if fuel dilution is a general problem with the engine, or specific to an operating mode. The following set of tests were performed in the following order:
1) For 143 miles after oil, oil filter and air filter change, I drove predominantly (>95%) on highway with low throttle settings (never above 1/4 throttle. Afterwards I took an oil sample.
2) For 51 miles I drove 99% highway miles alternating between high throttle (>3/4 throttle) and no throttle (similar to the famous Rubberband(tm) break-in method), with absolutely no wide open throttle used (WOT). Afterwards I took a second oil sample.
3) For 50 miles I drove 99% highway miles alternating between WOT and no throttle ... which was a hell of a lot of fun ... made me quite motion sick ... with no throttle settings in between. Afterwards I took a third oil sample.
4) For 40 minutes I parked the car in the driveway and let the engine idle. Afterwards I took a fourth oil sample.
After a week and a half, the results are now in, and here are the conclusions:
Fuel dilution does happen in this engine, as determined by several methods, Flashpoint being the most sensitive, and confirmed by Infrared Spectroscopy. The results are quite interesting. For the oil I'm using, the flashpoint of Motul 8100 E-tech 0W-40 is 430 F. After 143 miles at low throttle settings, the flashpoint of the oil reduced to 365 F. After 51 additional miles at high throttle settings (no WOT) the flashpoint was lowered to 345 degrees. However, clearly the largest change occured with WOT runs, where the flashpoint dropped dramatically to 280 F. And at idle for 40 minutes it stayed at 280 C. Here's a compliation of the results:
Baseline - Motul 0W-40 - 430 F - 0% dilution
Run_1 - Low throttle - 365 F - 0.85% dilution
Run_2 - High Throttle - 345 F - 1.1% dilution
Run_3 - WOT - 280 F - 2% dilution
Run_4 - Idle - 280 F - 2% dilution
The same trend can be seen in TBN numbers. TBN (Total Base Number) is a measure of the additive package acid acid neutralization capability.
Baseline - Motul 0W-40 - TBN 10.1
Run_1 - Low throttle - TBN 9.8
Run_2 - High Throttle - TBN 8.9
Run_3 - WOT - TBN 8.8
Run_4 - Idle - TBN 8.9
As fuel dilution occurs, the additive package of the oil is reacting to counteract the acids from the fuel, causing depletion of the add package. Just like adding chemicals to a pool or hottub. If you look at the numbers, 10% of the life of the oil was depleted in < 300 miles of driving. Now, part of this driving was extreme, even for my tastes, but it does show some interesting trends.
First, fuel dilution seems to be a consequence of this engine design, and most likely a consequence of having a direct injection nozzle squirting fuel into the chamber at 1500 psi. We can see this conclusively from the Run_1 results under extremely mild driving conditions.
Second, fuel dilution is proportional to the mass of fuel injected into the chamber. The more fuel, the more dilution, and is worse at WOT where the injectors run extremely rich, as has been shown by Kimbo's dyno plots.
For those naysayers that think the problem is one of poor ring seal, blow-by, or idling, these have been eliminated by either experimental design or further analysis results. Blow-by and ring seal are discounted for several reasons. First, this engine has near zero oil consumption and has since 1800 miles. It currently has consumed 1/4 Qt over the past 7000 miles. Second, all analytical measures of additional blow-by, such as Oxidation, Nitration and Soot are extremely low or non-existent. Finally, the engine was only allowed to idle for seconds before and after each run in the test. And at idle, there is no noticable increase in fuel dilution, eliminating this as a prime cause for previous fuel dilution measurement.
(As a side note, at idle the engine does not move enough oil to allow the diluted fuel in the oil to vaporize through the crankcase ventilation system. If the engine is again run at low throttle settings on the highway, fuel dilution numbers will decrease, as the fuel vaporizes away, to the level consistent with the average engine throttle setting.)
Based on these results, I am taking steps to improve the fuel dilution performance of the engine through some additional work with Terry, following his recommendations, and additional oil analysis. Some of these are considered proprietary to Terry and his business. However, if you want to get in on the fun, I would recommend other owners to do the following:
1) For new engines, change out the factory oil right after break-in, at 1500 miles, to get rid of the contaminated oil.
2) Do not go WOT at any time during break-in, until after you get the factory oil changed out. You'll just be pumping fuel into oil which has sheared and increasing the wear exponentially.
3) Use a good Audi 502 approved oil (for now) and change it early and often as the engine continues break-in, (1500 miles, 3000 miles, 5000 miles, 7500 miles), and then at 3000-5000 mile intervals thereafter.
4) Pick your favorite oil and have it periodically analyzed to determine the state of the oil in your engine. You'll be amazed at what you can learn from a good analysis and professional reading of that analysis.
5) Go here http://www.lubecontrol.com/fuel.htm and order some FP60 as a fuel additive, follow the instructions, and use it religiously. I can't tell you why, but trust me, it's a good thing for this engine.
6) Finally, I would highly recommend that RS4 owners work with Terry Dyson (http://www.dysonanalysis.com) to have their oil sampled and analyzed, so that as a group we can further track issues with this engine. The more data we have, the more informed we will be. And, the more data Terry will have to draw upon in forming conclusions and corrective action. For $50 per sample, you get to have his recommendations for your engine, driving style, environmental conditions ... etc. And much of that information is proprietary. I am implementing his recommendations currently. (AND, as an added bonus, you'll actually learn why your particular oil works the way it does, and why FP60 fuel additive is recommended.)
For those who want to get involved and sample your oil, I recommend the Dyson Premium analysis highly. Having compared it's results to Blackstone, it is superior in all aspects. However, should you need a method to sample your oil easily, I would suggest that you pick up a sampling pump from either Blackstone or Amsoil
Oil Analysis
http://www.dysonanalysis.com/premiumkits.html
http://www.blackstone-labs.com/pump.html
http://www.amsoil.com/storefront/detail.aspx?ID=3006
FP60
Odis Beavers
Phone # 214 929 2704/2703
or
http://www.lubecontrol.com/fuel.htm
I hope that a few of you find this information useful.
Finally, by way of disclaimer, I have no financial involvement with any of these companies or services. I use them, because they are good.
12-13-2006, 04:54 PM
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I don't think your conclusions are valid.
You would have to repeat the 'study' by doing every possible combination of the 4 run types (i.e. low, high, WOT, and idle in different sequences). The results you provide show an almost linear decline in fuel dilution and TBN....how do you know that isn't simply a function of the 'age' of the oil? After all, you didn't *change* the oil between the 4 different run conditions, you just took a sample....so the oil has progressively more mileage on it with each of the 4 run conditions. Changing the oil between each of the 4 run conditions (in each of the sequence variations noted above) would further strengthen the validity of the results.
HOWEVER...even if you did that, all you'd be showing is the characteristics of *your* RS4 motor. In order for the results to be valid for the entire population, you'd need a much larger sample size.
HOWEVER...even if you did that, all you'd be showing is the characteristics of *your* RS4 motor. In order for the results to be valid for the entire population, you'd need a much larger sample size.
12-13-2006, 05:02 PM
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Re: RS4 Fuel Dilution Study (very long and geeky)
Would you consider the possibility that the reason you're not showing more oil consumption is due in some part to the volume being added to the oil thru fuel dilution?
I would expect oil to be carried away with the fuel as it evaporates off thru the PCV system. In other words, it wouldn't be purely fuel separating from the oil in the system and evaporatiing off, but a mix...as it's already mixed thru the dilution.
Those are scary flashpoint numbers(280) for a synthetic oil. Of course, the fuel dilution adds to volatility and lower evap point.
It makes perfect sense that the direct injection is related to the high fuel dilution. I am wondering if this is a characteristic of direct injection engines in general, or if Audi blew it somewhere. Any insights yet as to that?
I'm wondering why the need to idle for 40 minutes for that test? Did you check for any water condensation in the oil too after that?
Finally, are you aware that you run the risk of freaking out a bunch of RS4 owners here?
I would expect oil to be carried away with the fuel as it evaporates off thru the PCV system. In other words, it wouldn't be purely fuel separating from the oil in the system and evaporatiing off, but a mix...as it's already mixed thru the dilution.
Those are scary flashpoint numbers(280) for a synthetic oil. Of course, the fuel dilution adds to volatility and lower evap point.
It makes perfect sense that the direct injection is related to the high fuel dilution. I am wondering if this is a characteristic of direct injection engines in general, or if Audi blew it somewhere. Any insights yet as to that?
I'm wondering why the need to idle for 40 minutes for that test? Did you check for any water condensation in the oil too after that?
Finally, are you aware that you run the risk of freaking out a bunch of RS4 owners here?
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12-13-2006, 05:19 PM
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Re: I don't think your conclusions are valid.
Very good points. With one exception...the oil wasn't aged if he only accumulated 300 miles or so total in his tests after an oil change. So, I don't think it's reasonable that any oil quality drop-off here is age related.
Your final sentence is particularly interesting and dead on, IMO.
Your final sentence is particularly interesting and dead on, IMO.
12-13-2006, 05:29 PM
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'aged' probably wasn't the best word to use.
'used' perhaps? not a lot of miles, but the conditions for each 'test' have to be the same (i.e. fresh oil) for the results to be valid.
what if the order of the tests was reversed (i.e. idle, WOT, high, low)....would the results be the same? we don't know.
I think this case study says more about the progressive nature of fuel dilution (which would be expected with any oil in any engine) than it does about any relationship between driving style and fuel dilution.
what if the order of the tests was reversed (i.e. idle, WOT, high, low)....would the results be the same? we don't know.
I think this case study says more about the progressive nature of fuel dilution (which would be expected with any oil in any engine) than it does about any relationship between driving style and fuel dilution.
12-13-2006, 05:43 PM
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Read all recent posts on engine oil and I am not a chemist or
automotive engineer so remain confused. Just got my RS4 this week and asked the tech at the dealership who said that the car has Mobil 1 and that I should use Mobil 1 5W-30 for winter in Mass. and 5W-40 the rest of the year. I assume that it conforms to the manual's guidance regarding the conformance with VW 502 00. What am I missing?