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Old 10-31-2019, 06:41 AM   #1
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DEF and Diesels

I am looking at used Tiffin Phaeton 40 QBHs. I have researched 2004 to 2012 year models. Love the floor plan and hope to full time in one in the not so distance future. All have Cummings engines which is the diesel engine I would like. In another thread a member mentioned by buying a 2011 coach I am buying a coach that is at the age where stuff starts breaking down. That got me thinking. One question is what year was the requirement to add DEF to the diesel engine added? Another question is does adding DEF affect the longevity of the engine? The coaches I am looking at have anywhere between 25K and 100K miles on them (most around 40 to 70K). In my research I have read that a well-cared for diesel engine will last for 200K plus miles but that the DEF requirement reduces the longevity of the engine and causes major repairs to be required much earlier. Is this true? Has the DEF requirement been around long enough that a reasonable determination can be made about the impact of DEF on diesel engine longevity?

Your thoughts and comments are greatly appreciated.
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Old 10-31-2019, 07:01 AM   #2
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DEF is injected into a component called SCR in the exhaust after system. I see no way it can contribute to decreasing overall engine life. If anything it could add to engine life because the use of DEF to reduce NOX emissions allows fuel combustion to burn at it's normal higher temp not smothered by oxygen depleted air recirculated by the EGR.
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Old 10-31-2019, 08:50 AM   #3
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Sounds like you think that DEF is added to the engine - it is not. It is a component in the post combustion exhaust treatment. The adoption of the SCR exhaust treatment system has resulted in better running engines and better fuel mileage. It has proven to be far more effective than the EGR systems previously used.

There is another component to diesel pollution remediation that you may have forgotten about - the DPF (diesel particulate filter). These remove soot and, in order to work effectively, need to regenerate occasionally. Excessive idling can plug them quickly and cause expensive repairs/replacements.

There are other things than the engine/transmission components to worry about in the year range of Tiffins you mentioned. 2009-2012 coaches had issues better known as the Big Three - roof rails, slide floor, and wet bay floor that Tiffin would have repaired if the owner brought it to their attention.
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Old 10-31-2019, 09:04 AM   #4
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My experience is that the DEF system breaks down and causes the expensive repairs as the miles accumulate. Further, even the really good repair places still don't know what's broken in the DEF system and how to fix it. As long as the engine, transmission, and other major components are properly maintained, they are as tough and bullet proof as the pre-DEF engines. Our Bus has over 110,000 miles and is doing fine, but the DEF system suffered a major failure on the way down from Alaska last year and a major truck repair place in Edmonton, AB took over 2 days work just to find the problem. Do a DEF search and read the many horror stories.
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Old 10-31-2019, 09:24 AM   #5
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DEF, like any system, is more apt to break down the older it gets. Aside from that, it is not particularly troublesome. Yes, there are outliers who have had DEF troubles, but this is out of the ordinary. All the new diesel coaches in the past 7 or 8 years have had DEF systems and you don't hear lots of problems with it. I would not let the presence or absence of a DEF system influence my buying decision.
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Old 10-31-2019, 09:43 AM   #6
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Quote:
Originally Posted by MRUSA14 View Post
DEF, like any system, is more apt to break down the older it gets. Aside from that, it is not particularly troublesome. Yes, there are outliers who have had DEF troubles, but this is out of the ordinary. All the new diesel coaches in the past 7 or 8 years have had DEF systems and you don't hear lots of problems with it. I would not let the presence or absence of a DEF system influence my buying decision.
Sorry, but I don't agree at all. For a good background on DEF problems check out DEF deletion, any way???
I'm not advocating deleting the deletion of DEF on my or your RV, but I think this thread nicely sums up the issue and what others are seeing, especially the long haul truckers.
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Old 10-31-2019, 12:38 PM   #7
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Originally Posted by Pigman1 View Post
Sorry, but I don't agree at all. For a good background on DEF problems check out DEF deletion, any way???
I'm not advocating deleting the deletion of DEF on my or your RV, but I think this thread nicely sums up the issue and what others are seeing, especially the long haul truckers.
If I intended to keep a MH for a very long time I wouldn't have any DEF issues

However older coaches that are now approaching 10 years since DEF showed up certainly have age issues as well

It is unfortunate the DEF system would up being so complicated and having so many sensors and other components
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Old 10-31-2019, 12:46 PM   #8
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Thank you, Thank you, Thank you all for your replies. I have a lot more now to think about but it seems DEF is an issue unto itself. I truly appreciate the comments and guidance. The more I read and research on here the more I know I don't know.


You are amazing!
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Old 10-31-2019, 12:57 PM   #9
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EPA2010 and later On Road Diesel engines are DEF compliant. This system includes, reservoir, pump, lines, heater and several sensors. And takes up mounting space on coach.
To get a true picture of the malfunctions that occur to DEF systems, check OTR trucking and diesel repair shop sites.
It is hurting the trucking industries bottom line.
Shops not so much.

But hey...clean air is worth it...right
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Old 11-08-2019, 09:25 PM   #10
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My grandchildren thank me for cleaner air. 40k miles no issues.
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Old 11-08-2019, 09:58 PM   #11
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YES, clean air is worth it. 55,000 miles and no issues.

Mark
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Old 11-08-2019, 11:44 PM   #12
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You're going to find a wide variety of reliability based on manufacturer for the three different emissions functions that could be on a modern diesel engine.

The selective catalytic reduction feature that uses DEF is just one of them. IMHO, this could be the least problematic of the three considering sensor failures or bad DEF quality issues are relatively easier to fix. However, I believe many SCR systems will start a countdown that begin to restrict your speed if not serviced if it malfunctions.

The Diesel Particulate Filter (nothing to do with DEF) can be a real pain if it clogs because it's not a regular paper filter you can easily change. Driving with a clogged DPF can damage other components.

The Exhaust Gas Recirculator (EGR) can be a significant problem if/when your intake is caked with soot. Driving with a clogged intake can cause other problems.

You will find older diesel engines without "DEF" that have a EGR + DPF or just the EGR. I think the EGRs started showing up on certain engines in 2003 and the DPFs a few years later.

All of these systems have made diesel vehicles less reliable than pre-2002 vehicles. Pick any car, truck, or motorhome manufacturer and you'll find a lot of evidence to support this reality.

I would look for an engine and chassis with the easiest procedure to replace the DPF, replace SCR sensors, and drain/clean the DEF tank.
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Old 11-10-2019, 09:27 AM   #13
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Does a DEF unit have EGR as part of the solution? Reading some of these post seems to imply that? If that is the case, you get the double whammy of DEF and EGR. Our EGR ISB has had a few issues with sensors and the clogged up horns. We are currently looking at a replacement coach for ours because we want a larger coach and our thinking is we want to avoid DEF because of problems associated with it and the lower cost of some 2007 -2008 units. Is that sound logic?
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Old 11-11-2019, 06:25 AM   #14
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SeattlePirat, the DPF (Diesel Particulate Filter) started on the 2007 chassis. We had it on our 2008 Monaco Dynasty. No trouble with it and it was the first year it was introduced. We drove that coach just under 70,000 miles in 7.5 yrs.

Some manufactures bought up pre-DPF engines as you might see one in a 2007- 2010 units.

Good luck on your search,
Mark
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