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Old 05-23-2008, 09:25 PM
Professional Novice
Join Date: Oct 2007
Location: Chattanooga
Posts: 190
86' 300SDL Fuel tank removal

Yes, our diesels are ALMOST perfect in every way...however we do have our issues of tank cleaning!

This forum has been my muse for everything diesel and a small unwritten rule of this forum is give and take...and that means, if you have been given information...TAKE the time to offer information to others who may have a similar problem

Diesels have a problem at times of water and growth in the tanks...Mercedes made their tanks somewhat easy to get to and clean out. You start under the car!

Step 1: Drain out your diesel...this is where you have a good drain pan and a little time to kill...pull off your supply and return lines and let the diesel drain...WARNING...MAKE SURE YOUR CAR IS CHOCKED IF YOU JACK THE BACK OF THE CAR UP! Unscrew the gas cap as this may give you a little extra gravity for draining. While youre there you can pull off the rubber boot around the filler neck...just pull gently with a pair of pliers.

Step 2: While the diesel is draining, you can open the trunk and remove the back truck wall with 6 8mm screws...3 on top 3 on bottom...and pull the wall out. The liners in the trunk may get in the way...just pull them out of your way.

Step 3: Now your diesel is all drained out...unscrew the fuel lines from the tank...this requires a 19mm wrench and some patience...DONT STRIP THOSES BABIES!!! Once out, pull off the rubber boot under the car shrouding the two lines. If you just cant get the torque for removing the one closest to the back of the car...proceed to step 4b.

Step 4: Back in the trunk, looking at the tank you will see 4 13mm nuts holding the tank to the chassis...2 on each side...remove them and their washers...remember to keep all these nuts and screws in a little canister so you dont lose em. Give the tank a little pull...there is a little adherance and may take a little wiggling (STEP 4B: If that one fuel line just wont work...heres a little trick...pry up on the tank alittle until the line is visible from the trunk and use a longer handled 19mm to unscrew it from the angle of the trunk.) Pull on the tank until you see the fuel sensor wire on the rear side of the tank...pull this wire off the sensor so you dont rip it out...dont get over zealous now!

Step 5: Youve probably dripped a little diesel in your trunk area but its out now...the whole thing weighs maybe 35 pounds when empty. Youll see on the tank where you removed the fuel lines, a hexagonal nut...thats your removable and cleanable fuel screen! This is where the health of your fuel tank will start to make itself evident! Mine was growing GREEN ALGAE!!! no wonder my filters never lasted long. To remove, I used a big adjustable wrench...however, this is where the advice of having a REALLY BIG socket set comes into necessity. Lucky for me, dad had a set. Nowhere is this more important than removing the fuel sensor! It dips into the curvature of the tank which makes it hard to get at it with pliers or wrenches...and you DO NOT want to strip THIS nut.

Step 6: Take a cloth and clean out the inside of where you removed the fuel screen...this is the sediment that may have helped clog this screen...there may be more than you think! The fuel sensor can be dipped in some diesel and allowed to fill up...then shake it a little and see what comes out! Now comes the cleaning of the tank itself...this is a baffled tank, so its not hollow on the inside...if you have a steam cleaner, that would work great...but for now, we will use the method I used. Get some extra strength paint thinner and pour it in whatever opening you want...shake up the tank a little and let it drain out whereever you can...I found that letting it drain out the filler did the trick! Youll see rust and grime. Now, flush out with a little diesel and go ahead and start putting it back together. Install the tank backwards of removal and remember all the boots you removed...we dont want water in the trunk!

Your car should be nice and clean in the tank! Remember to periodically use some good additives and biocide the tank every now and then!

Hope you enjoy! Good Luck!
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