I have a 300TD station wagon and noticed that it runs really rough when the tank is low. So I used the siphon tube and pulled as much fuel out of the tank as possible. It all came out pretty gray with some black bits. I intend to pull the fuel screen and clean it. It would probably also be nice to clean out the tank in place. Does anyone have a pretty solid process of cleaning the tank?

I removed my '82's tank entirely and cleaned it out with a pressure washer not too long ago. I used a hair dryer to dry the inside after washing as these tanks will start to rust if you introduce water to the inside and don't dry them thoroughly.

I think it gives peace of mind if you remove the whole unit and clean the screen at the same time. I also blew the fuel lines with compressed air from the front of the car to remove any possible debris and changed both fuel filters and replaced the fuel hoses that connect to the tank. Then you know for certain it won't get clogged up right after you put it all back together.

Check out this video:

https://www.youtube.com/watch?v=f5FTgoImqxo

I've never cleaned a tank in-place, it's easy if you remove it from the car first. The method I used that worked well, was to put some paint stripper into the tank, then a large handful of lag bolts. Cap/cork all the openings, then shake the tank vigorously, all around, from all angles. It's a real upper body workout! Then shake it around some more. Drain and repeat until it drains clean. Rinse and dry thoroughly. Then put some POR15 or special tank sealer product inside, and shake until inside is thoroughly coated. Let the excess drain, and let the product dry for a few days. Tank is cleaned, sealed, and ready for a few more decades of service.

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1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!

I think you can use some Star Tron it will clear up any algae in the tank and filter. You'd have to run a few tanks with it.

I would not pull the tank to clean it without looking inside to assess its condition first. That is easily done with a $15 borescope after you drain the tank. A W123 tank is well made/ rust proofed (unlike some US cars of the same era). Here's a pic of an 83 300D tank that was used as a WVO tank for about 3 years, after which it was removed and washed out with detergent and water then air dried and left outside for about 5 years before cutting it open. There is no rust on the outside or inside. What looks like rust spots on the bottom is actually dried up wvo residue.

This pic also shows a seldom seen inside of a W123 sedan tank. On the top middle is the vent tube (it was cut). Top right is the fuel sender hole. Big hole to the left of sender is for a floating WVO pickup. On the bottom left is the tank strainer hole. On the bottom right is the tank return nipple. As you can see, it is about 1/2" off the bottom, not half way up the tank as many on this forum erroneously been saying and continues to say to this day.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Sounds like algae plugging up the tank strainer. This is what I'd suggest:

-Buy some Startron for diesel and put it in the tank- follow directions provided.

- Change both filters

- loosen fuel filler cap and the fuel supply line in the engine bay (to the primary plastic filter) and blow compressed air into the supply line to clear the clog in the tank strainer. Don't do this with a full tank or you may spill some fuel out of the fill hole.

- Just drive the car and continue with the Startron treatment as you fill up. The Startron slowly breaks up the algae into small enough chunks so that it will pass through the strainer and the filters and slowly restore the cleanliness of your tank. A lot less work than pulling the tank!

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked