If I installed a 2 or 5 micron fuel filter inline with the 10 micron OEM filter on a 1985 300td , would that be too much resistance for the fuel pump to operate normally?
I was thinking I could just change out the 2 micron filter regularly and the OEM filter every once in while, plus if my fine filter plugged up on the road I could easily bypass it.

No.

Thanks.
Napa has a 1-14 filter head that accepts big filters. I hope I can find room for it. NAPA AUTO PARTS

The 10 Micron Filter is the Spin-on Filter.

If the Fine Filter plugs up on the Road it could be easier to change the Filter than to bypass it; depending on they type of Filter Assembly you are using.
The exception would be if you had some sort of Valve set-up that would cut the Fuel off from the 2 Micron Filter and divert the Flow to the 10 Micron Spin-on Filter.

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84 300D, 82 Volvo 244Gl Diesel

I have a Stanadyne FM-10 (5 micron) mounted on the support just behind the left headlight ('82 300D.). It is on the suction side of the fuel pump, so it doesn't "compete" with the secondary filter as far as pressure goes. The filters have a water drain built in and the mount has nipples that fit the OE hoses.

I am using a Racor 2 micron filter with a outboard primer bulb. Resistance is not a problem.

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Present
1987 300SDL
1991 300SL
1990 560SEL
2001 ML320

Past
1969 200D 1979-82
1983 300SD 1984-85
1972 250C 1982-02
1995 S350 2011
1997 S320 2012

On our 80 240D, I have a racor 200FG and use a 2 micron filter. this is my primarym and eliminated the small plastic one. If this one does plug up, I can take to top off, pull off the filter and reattach the top with it`s screw on band, primer pump it, or top it off with aft or oil, and drive off. the racor also has a large sediment bowl, and water drain.

Don`t worry about the feed pump not having enough oomph to pump the fuel. Boneheaddoctor had a plugged tank vent and the suction was collapsing his tank.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

I cant see the logic in placing a finer filter upstream.
If this new filter is filtering down to say 2 micron, nothing is likely to catch on the 10 micron. It is normal to have filters finer as you go.
Using that principle, one would place the 2 micron after the secondary filter, before the IP. This would maximize the life of both filters & minimize plugging of the 2 micron. That is what is done with large diesels in earth moving applications.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

In somes cases, logic is trumped by logistics.

A cat ir0750 or equivalent just looks like it would last a long time even at 2 microns. The stock filter would be staying clean. My reality problem is where to put an additional filter of that size. The left headlight area would even be difficult. The thing is, I filled up with B99 so that got me thinking about finer filtration. Since then, I've been topping off with dino. Probably B50 now- but the exhaust still smells like BBQ.

You are very correct, the finner filtration should be at each step down stream. when i got the car 2 yrs ago, the Racor was not hooked up, and looked like it was a looooog time since it ever was. they had the little plastic one in line. so I took the Racor apart and cleaned it up. the old fuel looked like dirty engine oil.

Reinstalled the assembly, and adden new hoses. then bought a new filter element at West Marine. they only had the 2 micron. I think they only come in a 2, 10 and 15 micron.

I have come across several older 240D, 300D and 300SD`s with these filters installed. I was talking to a retired MB mechanic, and he stated back when the increase of Diesel vehicles started arriving back in the early 80`s or when ever it was, the majority of service stations only carried gasoline and not diesel. so when stations started converting some of their tanks to diesel, MB had a lot of problems with people coming in with fuel related problems. so the racor`s were added.

Now I could splice into the line running from the secondary to the IP, and run it through the Racor and then to the IP. then add the little plastic prefilter back in line.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

As has already been said here, fitting a 2µ filter anywhere on the suction side of the lift pump or before the main filter makes no sense for a number of reasons. A fine filter works better and lasts longer with pressure rather than suction and replacement filter elements are not cheap @ +/- $45.

There is a bewildering variety of filter options in the Racor (and other) catalogues! I have always used a Racor R26S 2µ filter with screw on plastic bowl and water drain on these cars (i.e. the 225 R assy. 30 gal/hr). This is also a good choice for engines fitted with lift pumps that have no hand primer as the Racor 225R has a hand primer pump and bleed screw built into the mounting bracket.

I fitted one of these when my car was new between the main filter and fuel pump and has now nearly 900,000km. When I was running on Diesel I changed it every 2 years but since I started running on Jet-A1 15 years ago I have only needed to change the element once.

The initial cost is expensive and whether it is an economical proposition so late in the life of these old cars is probably questionable. Many of these cars have achieved very high mileage’s without them.

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Beagle

How does the filter "know" if the fuel is being pushed or pulled?

My 300td has 245K miles and runs really good with just the stock filter. I just want to preserve the IP, but no telling what else could go wrong.
A basic 1-14 filter head is pretty cheap; so are the filters, but I think it would only fit if i mounted it at an angle (would that be a terrible idea?).

The filter referred to above is designed to take up to 35psi from a pressure supply. Maximum suction available (to keep it in PSI) would be –14psi. and flow will be seriously restricted long before the vacuum gets anywhere near there.

The pressure supply and flow, on the other hand, will continue unabated until the pressure rises above 35psi and the filter element collapses. What this means in practice is that the filter will last up to twice as long.

Not a good idea! It would likely give problems bleeding.

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Beagle