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DPF and Regen....FUEL DILUTION....

11125 Views 8 Replies 6 Participants Last post by  gr8shot
I want to get up-to-date about this subject. I am a son of a mechanic that owns a 2008 Chevrolet Duramax and we are just starting to scratch the surface of the regen system in these trucks, Ford and Dodge too. So far we had learned that in a simplified version of the regen cycle, the truck will throw raw fuel into exhaust to heat up and burn off any unused fuel soot and particulates, note this only happens when EGT's don't get high enough through normal usage to do the job, so fuel is introduced. Now up until recently we were cursing the tree huggers and saving our four letter vocabularies for the whole system. But these feelings are more directed at the big three.

Now it gets interesting...A client of ours had his motor go down, not a Duramax, but one of the other two big manufacturers. Right now they want to know what oil he used in the truck. But what is more interesting is what was found in the oil analysis. Fuel dilution. This is not a small problem and it isn't going away anytime soon with any truck with a regen system. After learning more about this system it seems that the big three opted to do a cheaper regen system on these trucks, instead of an exhaust injected with raw fuel, they cut corners at the customer's expense and instead they designed the trucks to inject fuel in the exhaust stroke of the piston cycle...PROBLEM...This simplified solution is apparently causing diesel to end up in the crank case, thus the oil.....VERY BAD!! Diesel like most fuels is a solvent that is just going to break down the lubricity of any oil. If anyone is catching on to this and would like more info or would like to discuss, please let me know, I am also looking for paths and answers others have come across. It is an issue for us because A) We own a truck that has this problem, and yes, we did an oil analysis on our truck and we have fuel dilution in our oil too....No surprise, with the new understanding of this poorly designed regen system. We know a premium synthetic like Royal Purple or Amsoil will offer superior protection, but we will not do extended oil change intervals knowing that whatever oil we put in it will get diluted with fuel over the time extended past the recommended oil change interval. We are now going to change the oil every 3,500 mi. and do an oil analysis, if everything is ok, and no fuel dilution, then we will go to 5,000mi and then up to GM's recommended interval of 7,500mi, but nothing more.

This is something we want to be informed about so that no one else has to go through what our client is dealing with right now. We are also looking for alternatives. If the regen system is designed this way, then is there a way to save an engine by reprogramming the ECM to not do the fuel dump during regen. It sounds like there is more to it than just a few tubes of fuel running into the exhaust. I am all about the environment, but not at a $24,000 new engine price tag....And I encourage everyone to get an oil analysis done, it is a few bucks for the kit at your local auto parts stores and takes a few weeks to get the results mailed back. Especially if you are doing extended oil change intervals with a premium synthetic.:eek:
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Good read. We have been talking about this subject for a few months now. If you go to this link, it will get you up to speed from AMSOIL's perspective on this.

AMSOIL is also running a field study with their dealers that own diesel pickups with DPFs to get a trend for our products. Not sure how the test is going or when it will be completed.

What was the fuel dilution level on your truck? FYI, AMSOIL recently had an independent lab run the Kurt Orbahn Shear Stability Test then in that test diluted the fuel with 2% and 4% fuel. The results were amazing and impressive. That test is at the end of the thread I recommended above.

For the one you are repairing; why does the manufacturer want to know what brand of oil?

So when you say you are all about the environment, are you against just removing the DPF and getting the ECM reflashed? This will solve the problem and several guys have done this.

I see where you are going with analysis and drains however with AMSOIL they are advising customers to conduct analysis at OEM. If fuel dilution is less than 4% the oil is suitable for continued use. Something to take into consideration as you are figuring all this out.

Take care,
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Another thought....

I am glad it is on the minds of owners of these trucks already...I believe the test results showed about 3% after about 12,000 mi. but I will confirm that. As for the brand of oil, it seems that the truck manufacturer is trying to shift blame onto other parties. I am concerned about the environment but at what cost, especially if it jeopardizes the life cycle of an engine that has been proven to outlive the truck it was put into.

After thinking about this more, it seems that fuel dilution is only part of the problem.

Up until now, in a four-stroke engine cycle, diesel is only introduced at or right after TDC after a compression cycle. So this is keeping the fuel in the top portion of the cylinder.

The physics of a four-stroke...
The active regen is now dumping the same fuel into a cylinder that is empty, at or close to BDC, after the combustion cycle. This is where it gets interesting.
All of the cylinder wall is exposed to the raw solvent-like fuel, not just the top portion near the head. Adding to the problem, a diesel injector is designed to spray around 20,000 psi, (just a safe average, but most of the time, much more.) So now the fully exposed cylinder wall that would have proper lubrication on it, is now getting a 20,000psi pressure wash with a fuel that is known to dilute and break down the lubrication properties of ANY oil.

To top all of it off, the piston now travels up the same exposed walls because the diesel instantaneously mixed, thinned out the oil and sent it past the rings to the crank case to accumulate a fuel dilution percentage.

I am limited in some of the technicalities of this design so please inform me if any of this is incorrect, but as I remember the basics of a four-stroke, it seems like this is how it would work when you add a regen system like the big three have designed for these trucks. Please feel free to add info, correct or contact me about this, I will be searching for answers from anyone, owners and professionals alike until we all get the right grasp on this issue, it might just be the next Toyota design mishap.:eek:
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welcome to DF i would love to read but i am about to pass out on the computer i will read and reply later
You're right, it is a problem. However GM does take this into account in their DIC oil life calculations. If you watch, note the oil life % on the DIC before a regen, then note it after the regen. It will have dropped a significant % in just the few miles it takes to regen. This happens because of fuel dilution. Some people who do lots of in town driving and still have their DPF in tact only get 2000-3000 miles out of an oil change going per the DIC because of this.

The easiest solution is to get rid of the DPF system entirely. You can run a new exhaust system and modified computer tuning (via many available programmers) and the truck will never regen again. My truck runs better, gets MUCH better fuel mileage, has more power and probably most importantly to you... Going per the DIC, I can go close to 10,000 miles on conventional oil. I changed it last time when the DIC read about 25% life remaining, and that was a little over 7000 miles since the last change.

I agree with you that this is an overlooked problem. But it is one that does have a remedy. I couldn't possibly be happier with my truck now that it is DPF free!

Oh, and just as an FYI, the new 2011 LML duramax does have a 9th injector in the exhaust system to inject fuel into the exhaust which will facilitate the regen process, so no more fuel dilution. This also enabled the LML to be compatible with B20 biodiesel, compared to B5 on the LMM :)

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1. Get EFILive
2. Remove DPF
3. Re- Route PCV to atmosphere.
4. Turn off DPF with EFILive.
5. Turn off EGR with EFILive.
5. Enjoy the feeling of knowing that you vastly improved your truck.
Fuel dilution is a known concern with the current generation of diesels that use regens to clean the soot out of the DPF system, but I haven't seen it to be a cause for shortening the design life of the diesel engine.

The current diesels use multiple injection's of diesel during the power stroke and the LML's will have injectors that are much quicker and can be timed with even greater precision. During the regen process the injection timing is changed to allow for a later injection event which raises the exhaust temperature to burn the soot and change it to ash. The LML will have an extra injector for regen fuel, directly into the exhaust system which should reduce or eliminate fuel dilution in the oil.

Unfortunatly, I do not beleive the solution is simply to take off the DPF and turn off the regens as others suggest. Without pollution controls we wouldn't have diesel engines in our trucks today.

And no I am not a mechanic, nor do I work for the government, the tree huggers or the big 3, I have made a living in the oil industry for more than 40 years. Just as with gasoline engines the evolution of the diesel engines will take many years to reach the pollution vs efficiency balance?
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I am learning a great amount already. I do however have to say that the client's vehicle that shelled the engine is leased through a fleet company so there isn't a way to do the mods like EFILive and the DPF delete, they want it kept factory, and unfortunately they want a factory engine replacement. I am still interested in learning more about the internal mechanics of how the fuel is being introduced in the exhaust cycle. Besides fuel dilution in the oil, I am interested in finding out if this is causing excessive wear of the piston wall, piston and rings. After reading some of the findings on our client's vehicle, it seems like a very distinct possibility. I guess time will only tell with these trucks as I also believe that they haven't been in service long enough to prove if there is excessive wear occuring because of the regen system.
There's 100% stock LMM's out there with 200k plus miles already, I've seen a few for sale. So they'll at least last that long.
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