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Old 11-12-2015, 09:15 PM   #1
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Diesel Generator Retrofit


We have a new to us, 1997 Tiffin 32DP that has a Onan Marquis 6500 LP generator. It runs great, but with the installed 100lb LP tank, the refuel times are very short for our needs.

Currently, the tank provides about 20 hours worth of run time for the A/C and appliances. Initially we thought about adding 2 30lb horizontal tanks in the storage compartment to supplement the main tank. But, that would still leave us with the task of searching for LP every few days.

Our last coach was a 32' Class C that utilized a single fuel for both the engine and generator and provided much more flexibility. We could fuel the coach and run the genset for 35-40 hours before topping the tank.

So, has anyone retrofitted a Diesel. Looking on the web, it seems like a decent used unit can be purchased for $3,500 - $4,500.

The issues that come to mind are wiring differences and plumbing the fuel supply lines to an installed fuel tank. With the number of coaches that came with LP generators, it seems that someone must have at least considered a LP to diesel swap.

Any help or insight would be appreciated,


J. R. & Lisa
97 Tiffin 32 DP, Freightliner Chassis, Cummings 5.9 275HP ISB 24V.
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Old 11-12-2015, 09:20 PM   #2
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I considered it, then traded the whole rig in for one newer and equipped the way we thought we wanted. That was in '02 so some years ago.

2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
Charter Good Sam Lifetime Member, FMCA, SKP
RV'ing since 1957, NRA Benefactor Life, towing '05 Odyssey
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Old 11-13-2015, 08:42 PM   #3
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Anything is possible given enough time and money.

The generator footprint I would think is the same as a similar size in diesel. I would also think that the wiring harnesses are the same. The hardest part may be the plumbing to the diesel tank. Normally there is a completely separate fitting that with pipe that pulls fuel from the tank that is high enough to allow for ~25% fuel as reserve. If your tank doesn't have a separate fitting for generator installation it may be a problem since I would tap into the line going to the engine.

Another option to consider is to carry a smaller generator and run it when you think you will be using more generator time.
Jim J
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi
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Old 11-13-2015, 09:58 PM   #4
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I believe most diesel generators are water cooled. They're also much heavier. I have the same situation. My propane generator is mounted under the coach between the driver & passenger seats. I don't see any way I could get a diesel fitted in this small area.
1988 34' Executive Industries - Executive Prestige
5.9 Cummins, Allison AT542
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Old 11-13-2015, 10:09 PM   #5
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Our gen is a 12.5Kw Onan, weight is 787#'s, and measures 41.4"L x 24.5"W x 27"H.
But then that's far more than most rigs need. Our dryer is a 240 volt unit so it does need the 120/240 output and we have three heat pumps.

The 6.0 and 8.0 QD diesels are:
36.3" L X 23.6" W X 22.3" H
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
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diesel, generator

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