Valve coking and direct injection engines
12-10-2016, 12:37 PM
#41
They have made great progress as far as the oil consumption, but in doing so are greatly shortening engine life. They are internally spearating much of the oil mist from the PCV vapors and returning them to the crankcase, but this also results in most of the contaminates present that were evacuated with the oil mist prior to also be returned to the crankcase overloading the engine oil with the contaminates, raw fuel being the greatest next to water vapor. So it is a tradeoff. Engine longevity for less oil consumption and reduced rate of valve coking. Most automakers are doing the same. It seems the trned is get them to last 50k miles on average as 90% trade before that mileage is reached, and then it becomes a secondary market issue out of their hands. GM and Ford and a few others have lowered engine warranty periods to 36k miles on all GDI engines, and I expect to see the rest follow suite.
This will have a huge impact on the aftermarket warranty companies as they figure loss rates at the standard of port injection engine lasting several hundred thousand miles with proper care, so extended warranties being primarily aftermarket insurers, the loss ratio will turn them upside down in a hurry.
Almost none of this is releasd to the public is a crime IMHO. Prospective buyers and current owners need to know this is a new era in engine care and be educated accordingly. The fear is a backlash on new vehicle sales, and that would be devastating to the industry.
This will have a huge impact on the aftermarket warranty companies as they figure loss rates at the standard of port injection engine lasting several hundred thousand miles with proper care, so extended warranties being primarily aftermarket insurers, the loss ratio will turn them upside down in a hurry.
Almost none of this is releasd to the public is a crime IMHO. Prospective buyers and current owners need to know this is a new era in engine care and be educated accordingly. The fear is a backlash on new vehicle sales, and that would be devastating to the industry.
12-10-2016, 07:29 PM
#43
Not as much as gasoline engines. First, the Diesel combustion cycle is a lot less dependent on a critical fuel/air mixture to operate effectively. So as the carbon might build up it will take longer to affect performance and driveability. Secondly, direct injection Diesels have been around for a long time without widespread report of these problems. Finally, modern Diesles with complex emissions control systems have egr coolers which condense more of the oily vapor coming from the engine and reduce the amount of carbon buildup.
12-10-2016, 07:34 PM
#44
They have made great progress as far as the oil consumption, but in doing so are greatly shortening engine life. They are internally spearating much of the oil mist from the PCV vapors and returning them to the crankcase, but this also results in most of the contaminates present that were evacuated with the oil mist prior to also be returned to the crankcase overloading the engine oil with the contaminates, raw fuel being the greatest next to water vapor. So it is a tradeoff. Engine longevity for less oil consumption and reduced rate of valve coking. Most automakers are doing the same. It seems the trned is get them to last 50k miles on average as 90% trade before that mileage is reached, and then it becomes a secondary market issue out of their hands. GM and Ford and a few others have lowered engine warranty periods to 36k miles on all GDI engines, and I expect to see the rest follow suite.
This will have a huge impact on the aftermarket warranty companies as they figure loss rates at the standard of port injection engine lasting several hundred thousand miles with proper care, so extended warranties being primarily aftermarket insurers, the loss ratio will turn them upside down in a hurry.
Almost none of this is releasd to the public is a crime IMHO. Prospective buyers and current owners need to know this is a new era in engine care and be educated accordingly. The fear is a backlash on new vehicle sales, and that would be devastating to the industry.
This will have a huge impact on the aftermarket warranty companies as they figure loss rates at the standard of port injection engine lasting several hundred thousand miles with proper care, so extended warranties being primarily aftermarket insurers, the loss ratio will turn them upside down in a hurry.
Almost none of this is releasd to the public is a crime IMHO. Prospective buyers and current owners need to know this is a new era in engine care and be educated accordingly. The fear is a backlash on new vehicle sales, and that would be devastating to the industry.
12-10-2016, 07:59 PM
#45
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Not as much as gasoline engines. First, the Diesel combustion cycle is a lot less dependent on a critical fuel/air mixture to operate effectively. So as the carbon might build up it will take longer to affect performance and driveability. Secondly, direct injection Diesels have been around for a long time without widespread report of these problems. Finally, modern Diesles with complex emissions control systems have egr coolers which condense more of the oily vapor coming from the engine and reduce the amount of carbon buildup.
12-11-2016, 08:56 AM
#46
Not as much as gasoline engines. First, the Diesel combustion cycle is a lot less dependent on a critical fuel/air mixture to operate effectively. So as the carbon might build up it will take longer to affect performance and driveability. Secondly, direct injection Diesels have been around for a long time without widespread report of these problems. Finally, modern Diesles with complex emissions control systems have egr coolers which condense more of the oily vapor coming from the engine and reduce the amount of carbon buildup.
Understand, we have worked on R&D of these engine since 2008 when we were contracted to study the intake valve coking issues, and since we have learned far more about the oil contamination and raw fuel wash-down, etc.
I am happy to share lab results, etc. and as much as NDA's don't prevent us disclosing. I assume your well versed on reading oil analysis, etc. coming from the diesel World.
Cheers!
12-11-2016, 09:11 AM
#47
AudiWorld Senior Member
I don't read what GDI is saying to mean engines will not last beyond 50K miles. I read him as saying that manufacturers' strategy is to get the engines to 50K (warranty expiration in case of our A6s) without any valve coking issues presenting, thus no warranty claims related thereto. I agree, would be hard to believe that our engines will be toast after 50K with reasonable care. However, what I do believe is that we stand a good chance of having the valve coking problem after warranty expiration and may need to bear cost of a valve cleaning.
Not to sound like a broken record (and please guys, don't flame me) I will continue to adhere to my 5K oil change intervals and in fact am going to shorten it a bit and change every 4 months regardless of mileage. I pulled the dipstick out of wife's /13 Volvo S80T6 and compared side by side with my 3.0T A6. Volvo oil while not as clean as when changed is still amber in color with 3300 city driven miles. A6 is very dark in color with 2,000 miles since last change and of those 2,000 miles 500 were a highway trip. I know this is not scientific and it would be interesting to send samples from both cars next oil change to Blackstone for analysis (I may well do that) but there is a significant difference in color which leads me to believe GDI's statements to the effect that there is much more oil contamination in DI engines are correct. Note the S80 does not have DI. It is a 3 litre straight 6 turbo and similar to the A6 full synthetic oil is required.
I wonder if there was a nefarious purpose in doing away with the dipstick in our cars -- if you cant pull the stick, you can't see how black the oil is. Less questions for the service department perhaps.
Best,
Jeff
12-11-2016, 05:16 PM
#48
AudiWorld Super User
If oil color is an indicator (GDI Tech seemed to indicate it is not), my A6 oil after 9K miles is still amber. In fact, I can hardly read it on the dipstick. Therefore, I'm not sure the color makes a difference re valve coking. I guess I may have it done at some point but at 48K miles, I don't feel it's time quite yet. I'm pretty observant when it comes to my car and I feel no difference whatsoever in performance despite what has been written here. At the same time, I appreciate what has been presented here.
12-11-2016, 06:17 PM
#49
AudiWorld Senior Member
If oil color is an indicator (GDI Tech seemed to indicate it is not), my A6 oil after 9K miles is still amber. In fact, I can hardly read it on the dipstick. Therefore, I'm not sure the color makes a difference re valve coking. I guess I may have it done at some point but at 48K miles, I don't feel it's time quite yet. I'm pretty observant when it comes to my car and I feel no difference whatsoever in performance despite what has been written here. At the same time, I appreciate what has been presented here.
I'm going to collect samples from both the S80 and the A6 when oil is next changed and send for analysis. Both cars are driven in a similar manner and for the most part used as commute vehicles in the city. It will be interesting to see the results.
GDI Tech please weigh in regarding oil color question, thanks.
Sportstick lives 15 minutes from me. I'm curious to see what the oil looks like in his A6 after a couple of thousand miles. I'll have to take a look next time he and I get together. We use same Audi dealer so there should be no variance in oil brand between the two cars.
Final word. No one should get too excited about this issue. As I've said before, if all it takes to mitigate the problem (which may not affect some of us) are frequent oil changes, top tier fuel and the need to de-carbon the valves somewhere north of 50,000 miles it is not the end of the world.
Best,
Jeff
12-12-2016, 03:08 AM
#50
The DFI engines produce more soot and this will turn the the color of the oil dark/black sooner. The Diesels I have had in the past turned the oil black within a thousand miles or so. It means there is soot in the oil and the oil detergent package is doing its job in keeping it dispersed. The question, I believe, is how much of that oil is being directed to the intake valve area.