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Old 04-05-2002, 08:21 PM
Posts: n/a
This is to those that say it's madness to use the fuel from the old filter to prime the new one. The fuel in the old filter isn't fuel that has been sitting there the past 5 years since you last changed the filter, it's fuel that just came from the tank. As for buying a gallon can for diesel and filling up the new filter with it and pouring the rest in the tank--well thats just silly, the diesel you pour into the new filter from the can and then pour into the tank is the same quality unfiltered fuel that is in the old filter to begin with!
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Old 04-06-2002, 04:56 AM
The Warden's Avatar
Certified diesel nut
Join Date: Mar 2002
Location: Pacifica (SF Bay Area), CA
Posts: 2,946
One thought on using (or not using) the fuel out of the old filter in the new one.

I'm not gonna say that doing so or not doing so is "madness", but if you fill the fuel filter completely with fuel from the old one, depending on the design, you could get unfiltered fuel going through the injector pump and into the injectors. The pump itself has very fine tolerances (one reason why having any water mixed in with the diesel can be such a bad thing), and the injectors are pretty similar.

I don't know exactly how M-B filters were designed, but the filters on my Fords are similar to oil filters (in fact, they're the same outer diameter). Just pouring the fuel into the holes on the outer rim is extremely difficult, and pouting the fuel into the center hole will result in that fuel going into the injector pump, quite possibly (depending on where in the old filter it came from) not having been through a filter at all. Having two filters negates this to a degree, so it's safer to do so on a Benz (Ford, in their utmost wisdom designed the fuel system on the 6.9l's with only one real filter; there's a second one on the firewall that's useless and supposedly serves mainly to separate water from the fuel), but, personally, I'd prefer to hand-pump and/or crank the engine extra long, to even slightly risk lowering the life of an injector pump...for a Ford, they run over $300 easily; I'd hate to see how much an injector pump for a Benz would cost *lol*

Just my $.02...again, not preaching, just offering my opinion. Keep on dieselin'...
2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
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Old 04-06-2002, 06:03 AM
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Join Date: Dec 2001
Location: San Jose, CA
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I shall repeat my comments from a previous post--

It's madness!
Don't ever pour fuel from an old filter straight into the middle of the new filter!
You are pouring the remains from the debris/detritus from the WORN OUT FILTER directly into the fuel line to the injectors, without filtering it at all.

I don't see why this thinking is incorrect...? If someone does, let me hear it!

Madness, I tell you...
1981 300CD (Benzina)
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Old 04-06-2002, 06:28 AM
84300DT's Avatar
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Join Date: Jan 2002
Location: Mass.
Posts: 2,218
fuel filters

yes, i am guilty of pouring fuel from the old filter into the new one prior to installing, but, for sure i checked it first with a glass jar and made sure there was no crap floating around in it - and there wasn't. the fuel was clear and clean. i would never pour dirty fuel into a new filter aye that is madness! Also the primer pump on my car is the old style so if it was possible i did not want to disturb it and maybe cause a bigger problem/fuel leak. Anyhow, the bottom line is that after one week with the new filters the car performs much better and the new in line clear filter is absolute clean. I realize i may have dodged a bullet and using the pump is prolly more desirable in an ideal world
1984 300D Turbo - 231k....totalled 11/30/07 RIP
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Old 04-06-2002, 06:07 PM
Holson Adi's Avatar
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Join Date: Jul 2001
Location: Boston, MA
Posts: 2,561
I just did mine today, instead of putting the old fuel back, I just put it in a jar.. and I'll use it for cleaning parts, etc.
My hands still smelll like diesel fuel..
I primed it manually (didn't take too long) and it started right up and it immediately tried to kill itself.. put some throttle in then it idled perfectly...

When I was fixing it I saw an old lady in a pre-80 300CD Diesel... She drives past my car every now and then (maybe she wants to see another 300CD)..
I only wish it was a hot girl instead...
Probably won't happen.. i bet they prefer to drive Mustangs, Cherokee, etc.. oh well.

I did meet this girl who actually fixed her own beat up Toyota Corolla! That was cool.. though she was not exactly hot.
2008 BMW 335i Coupe
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Old 04-06-2002, 06:45 PM
Randall Kress
Posts: n/a

I had the fuel filters changed today at the dealership. My guy has been known to say, "fill the filters up with ATF" when installing. ATF is a factory rec for fuel filter installation, if not, he couldn't do it to customers cars... ATF has detergents and it gives the injectors a quick shot of cleaning... But I will say this, my car performs no better than it did with the old filters. None!
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Old 04-07-2002, 10:28 PM
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Join Date: Jan 2000
Location: PA
Posts: 5,440

Like I said before, if the fuel filters are not about 90% restricted, there will be no difference in the performance of the engine..

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Old 04-08-2002, 02:40 AM
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Join Date: Aug 2001
Location: USA
Posts: 7,970
Using the primer pump is great if you have one. Install the filter dry and pump it up by hand, that way you don't need to fret about subatomic particles entering the I/P or injectors.

HOWEVER, for those of us with the newer engines (OM60x) we don't have a primer pump. Mercedes designed these I/P's with a self-priming, high-volume fuel pump. Long periods of cranking are NOT good for the cylinder walls, battery, or starter. You need to fill up the can with SOMETHING. And, as LightMan said, ATF belongs in the tranny, for exactly the reasons stated. If you must use something for cleaning, or want to fill the new filter with something other than diesel fuel, then use a can of Diesel Purge!

This whole procedure is enough of a PITA that I don't replace the secondary filter very often - once every few years, or several tens of thousands of miles, if not longer. I keep an eye on the prefilter and replace that when needed, which isn't very much... like PEH said, the filters need to be pretty plugged up to actually limit performance!

Dave M.
Boise, ID

1997 E420 - 155kmi (Bugeyes)
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