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Old 08-11-2015, 04:49 PM   #1
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Cummins 425 ISL, Pre Def.

I have never been on a forum before, so if I make a mistake please excuse.
My question is: I am looking at a 5 year old motorhome with a Cummins 425 ISL, Pre Def. I don't know what "Pre Def." means. Good or do I worry?

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Old 08-11-2015, 05:17 PM   #2
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This is a great place to learn what you need to know before you buy. This may help.
What Year Diesel Engine To Buy? - Engines - FMCA Motorhome Forums
2 stroker

2006 Country Coach Inspire 360 40ft Genoa Designer Series, Samsung 197 RR
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Old 08-11-2015, 05:25 PM   #3
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Originally Posted by ceggera View Post
I have never been on a forum before, so if I make a mistake please excuse.

My question is: I am looking at a 5 year old motorhome with a Cummins 425 ISL, Pre Def. I don't know what "Pre Def." means. Good or do I worry?

The EPA required all Diesel engines produced after 1/1/2007 to be equipped with a diesel particulate filter. Then in 2010 the EPA required a reduction in NOX that most manufacturers met with DEF(diesel exhaust fluid). In both cases, coaches were able to push off the requirement about one year by purchasing engines in advance. By all reports, these systems are working pretty well but they do introduce a high level of complexity.

Steve Ownby
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Old 08-11-2015, 06:25 PM   #4
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Our rig has the DPF, and they do break internally, cost was $2,500 for a new one and I don't know what the install was since it was done as part of the top end overhaul after the valve broke in #6.
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
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Old 08-12-2015, 11:45 AM   #5
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As far a I'm concerned, if it has the floor plan you like, the price is right and it's in good shape, buy it . When I decided to move up to a DP I purposely went looking for a non DEF/DPF unit. Reason? Less to go wrong and maintain. I have the same engine in my coach, ISL 350, and love it's power, reliability and my fuel mileage is not bad either (avg. 9mpg pulling a GCVW of 34,000lbs). What make of coach is it in?

Craig & Carolyn Roberts Apple Valley, CA
2006 Newmar 3910 KSDP 400 ISL Cummins Spartan Mountian Master Chassis
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