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Old 04-25-2015, 01:00 PM   #1
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Symptoms of a Dirty Diesel Tank???

I have had my 2005 Phaeton for a year now. In that time I have had the Onan 7500 generator fuel filter changed three times. I think they were supposed to do it at PDI as well, but I'm not sure they did. The problem is that the generator begins quitting after running an hour or so, then a day or two later it will be after a half-hour, then 10 minutes, then 2 minutes, then it won't run at all. Changing the fuel filter fixes it. The propulsion engine runs fine, and I haven't had to change its filters except for last fall's yearly PM service.

I'm wondering if I have a dirty fuel tank. The filter has clogged twice after I have filled the 100 gallon tank when it was less than a quarter full. (It normally doesn't get that low as most of our camping is less than 100 miles away, and I always fill it up before parking it.) I'm thinking that the big-gallon fill stirs up crud from the bottom of the tank.

I was thinking of draining some fuel/crud off the bottom of the tank if there is a plug, but I read in another thread that there should be a hazmat crew on site if one is dumb enough to try that. I was also thinking of having the fuel polished, but that wouldn't clean the tank.

To those of you with more experience, does it sound like a dirty tank? If so, what do I do now? (I know that I have to learn to change the fuel filter myself, and I have a filter on hand, but the coach had to go to the shop for another matter so I had them do it last week.)

As always, thank you for providing my continuing motor home education.

2005 Phaeton 40 QDH
2013 Honda CR-V
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Old 04-25-2015, 01:10 PM   #2
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Truly an odd problem ; because ; the pick-up tube for the gen set is suspended in the tank 1/4 the way from the bottom, so any crud in the tank should be way below the tube and be sucked into the engine first.
Have you cut open any of the gen set filters?
I'd be leaning towards the flex hose from the tank to the generator , having a hole or loose connection allowing it to suck in dirt. Or the hose breaking down internally and passing that debris into the filter.

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Old 04-25-2015, 01:31 PM   #3
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Doesn't your engine have primary/secondary fuel filters?
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Old 04-25-2015, 01:44 PM   #4
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Have you ever run the main engine, below 1/4 tank?

It is possible, you have the pickups crossed and the generator is getting the dirty fuel, from the bottom of the tank, thru it's small filter.

Not sure how to check, besides driving until 1/8th tank. If the MH dies, at least you will have the generator.

You should cut open the old filter, to see what your collecting in it. That may help.
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Old 04-25-2015, 04:49 PM   #5
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If you've got algae growing in the tank you'll continue to have problems unless you treat. When I first bought my RV, the first time I changed the fuel filters I had a huge amount of a black slime on top of the filter, almost completely plugging it off.

I now use an algaecide "Biobor", I will put in a dose whenever the RV will be parked for any length of time. You can find this a most big truck stops.

I also fill the tank to reduce build up of condensation.

The algaecide will kill the algae but the dead algae will still be in the tank. Startron makes an enzyme that will basically dissolve the dead algae, I've recently started to use this also.

If you do have a significant amount of algae you may have to do a tank cleaning.
Jim J
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Old 04-25-2015, 06:58 PM   #6
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I would look up fuel polishing in the yellow pages and have that service performed and then treat your new fuel with a biocide to prevent future algae. They have a suction hose that pulls fuel from your tank, runs it through very large filters and returns the polished fuel to the tank. The return is a high pressure spray that helps knock the crud off the tank walls and stirs it up so it can be sucked out. A little spendy but less than tows and constant filter changes.
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Old 04-26-2015, 08:27 AM   #7
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My guess is that you have either a deteriorating fuel line on the genset feed or some gunk in the tank. The genset filter is small and will clog up faster, plus the engine has a two-stage filtering system that traps larger particles in the primary. It's possible you do have some clogging in the engine filters as well and you might not notice it except under heavy acceleration or hills climbs. The fuel flow may be restricted but not stopped altogether.

Sometimes a deteriorating rubber fuel line causes filter clogging as bits of soft rubber flow into it, so it's conceivable there is a fuel line problem to the genset alone.

Gary Brinck
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