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Old 10-24-2021, 11:56 AM   #1
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Fuel filters

I recently purchases a 2018 Tiffin Allegro Red motorhome with a 360 HP Cummins Diesel. The instructions for changing the fuel filters is to per-fill the new filters with clean fuel. Can the fuel from the old filters be used in the new filters? If not, what would you suggest?
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Old 10-24-2021, 12:01 PM   #2
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Don’t use the fuel from the old filters. Get a small portable fuel can designated for diesel(usually yellow color). And go to a filling station, put some diesel in it and fill the new filters from that.
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Old 10-24-2021, 12:03 PM   #3
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I don't know the correct "prime" procedure for your engine, but I can tell you that you do NOT want to use fuel from the old filter to prime the new one.

The outer holes are the INLETS for the filter, so any fuel you pour out of the outer holes will not only be unfiltered, but likely contaminated with anything the filter has collected.

Hopefully someone else who has first hand of how Cummins recommends priming your engine will chime in.

An excellent choice would be to call Cummins tomorrow with your engine serial number and ask them.

There are a lot of "here is how I prime mine" answers, but they may or may not apply to YOUR engine.

Cummins 800-286-6467
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Old 10-24-2021, 01:04 PM   #4
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It's never a good idea to use the fuel that has collected in an older filter in a new filter. Typically, the old filter collected most of the debris within the element, but larger pieces cold pour out when emptying the old filter. Water and algae could also be in that fuel.

Buy a small one gallon fuel can and fill it with diesel for your fuel filter changes. Prefill the filters by placing a cap over the center hole or a clean thumb and pour the new fuel in around the edges. Go slowly as the fuel will take a little time to absorb into the element.

Many coaches will leak fuel while changing the filters, tilting the coach forward with the jacks can help stop gravity flow.

I like to remove and replace the primary filter, usually the large one with a drain and electrical connections. On some coaches/engines, there is a pump on top of that primary filter. The pump looks like the bottom of a can, about 1.5" in diameter. If you have one, it will often have a slip on rubber cap. If your coach has the pump, depress it until it gets firm.

Once the primary is installed, I start the coach and let it idle for a few minutes. Once I know it's running well, I move to the primary filter. Remove and replace with a completely full filter.

Once it's installed, most Cummins engines will let you prime them by turning the ignition on, without starting the coach, wait 15 seconds and then turn the ignition off. Do this 3-4 times and then start the coach.

Many will come on here and say just put them on and do the engine priming with the ignition, as described above. I've found that to be problematic and the coach didn't want to start. I think many regurgitate that procedure from the engine manual, but have never done it successfully themselves. Either way, it's just not worth taking the chance.

It's a good idea to always carry a spare set of filters while travelling. Carrying a couple of quarts of Diesel Service Power Kleen, available at Walmart, can be used in place of diesel fuel for an emergency filter fill on the road.
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Old 10-24-2021, 06:30 PM   #5
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Originally Posted by Mr Lars View Post
Donít use the fuel from the old filters. Get a small portable fuel can designated for diesel(usually yellow color). And go to a filling station, put some diesel in it and fill the new filters from that.
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Old 10-24-2021, 07:21 PM   #6
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You can also use Dexron ATF fluid to fill your filters.
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Old 10-24-2021, 11:09 PM   #7
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carolou, read this:

Originally Posted by grldst View Post
You can also use Dexron ATF fluid to fill your filters.
Not with the DEF engines, the ash content will cause problems.
2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA." My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy
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