i'm not sure what's involved with changing the fuel filters...i know something has to be done to get the air out of the fuel lines, but i'm not sure how to accomplish this. i read 300SD Fuel Filter Replacement Instructions which was helpful in explaining how to change the main filter, however i didn't see anything pertaining to ridding the fuel lines of air once the filter is installed. also, i'm not sure how to change the prefilter. could someone please advise me in this matter? thanks

First, the pre-filter is easy. Just unscrew the clamps and pull the fuel lines off. I would have a roll of paper towels on hand to catch the fuel. As for the main filter, once you have put the new filter on, you loosen the nut on top, I think it's 15 mm. I don't mean the one that holds the filter on. It's just to the left of the filter nut. It's the one that the return line is attached to. Then down by the pre-filter you will see either a black plastic knob or a white knob. This is the hand pump. Now, if you a white one, you will need to unscrew it a bit to free it up, and start pumping it. This will manually pump diesel through. When pure diesel, versus air bubbles, come from that loosened bolt, your done. Just tighten the knob up. If you have a black knob, you just need to pump it. By the way, to save on pumping excess air out, you could pre fill the main filter with diesel. Also, I would recommend you go to Pep Boys or the alike and buy a Haynes manual for the 123 series diesels. This covers the 240's and 300's. In there you will find pictures (photos) of the procedure I just described.

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Rick,
No need to loosen the banjo bolt, just replace the prefilter and pump the lift pump until the filter is full of fuel. You will then notice a difference in the pumping pressure and possible a different sound as the air is all removed from the main filter.
I pump until the prefilter is full then start the engine. No issues at all.!

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

I always use a Channel Lock pliers on the fuel supply hose to keep from losing fuel when changing the primary.....

While pumping my white handled pump to get all the air out, I was getting leakage of diesel around the handle. Is this normal? Should it leak around the pump?

I also loosen the 21mm nut that tightens the filter to pump up the line, not the one with the banjo bolt. Seems to me that I read in the manual that you do it that way.....

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1998 W202 C230 - The money pit of late.
1984 W126 300SD (356,800 miles) Gone to the wrenchapart
1984 W123 300D Gone to the wrenchapart
1972 W108 280SE 3.5 (sold but not forgotten)
1986 Buick Grand National 3.8l Turbo (86k miles)
1966 Glassic Model 'A' Replica http://www.glassicannex.org

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The older style white plastic pumps almost always leak when you pump them. If the leaking gets really bad then it will get harder to pump without getting more air in through the pump. A little/medium amount of diesel slober is OK. The newer black ended replacement pumps won't leak at all. Make sure you screw the white style pump closed all the way when you are done.

jacrouch,
As a suggestion you may want to replace the fuel filters when the engine is warm (as opposed to stone cold) and with at least a half a tank of fuel. You'll find it will start easier if you don't get 100% of the air out. A little bit of residual air will usually come out once you get the engine going but it can make a difference in trying to start a stone cold engine. A full tank eases the process too because you get a bit of gravity feed to help you out. Also when you replace the main filter (the one that looks like a small oil filter) look for a couple of rubber O-rings on the bolt that screws into it from above. If they are hard they should be replaced. (They're cheap so if in doubt just replace them)

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold