240D algae part 5 – Sealing the W123 fuel tank

In the last update, I cleaned out all the junk from my W123 fuel tank.  At the time I was undecided if I should do anything about the surface rust in the bottom of the tank.   In the end I decided to.   The rust was just surface rust, but it covered quite a lot of the bottom of the tank.   My general preference for doing things properly kicked in, and I decided to seal the tank.

One of the things that got me over the line was that the tank does not have a swirl pot like the petrol engine cars.   On the petrol cars, I would be worried that the sealant would block the small hole in the swirl pot that lets fuel from outside the pot be drawn inside.   On the diesel, I would not have to worry about that.    I’m actually kind of surprised there are no baffles or anything like that to stop the fuel sloshing around during hard cornering.  I suppose the assumption is that diesel drivers don’t do stuff like that.   Challenge is that many of these cars were taxis and clearly the MB engineers never met a Sydney taxi driver.  I’ve even taken my car on a lap of eastern creek raceway.

Sealing the tank added another week and a half to the project.   You can’t just buy the tank sealers at Repco or Supercheap, so first it took 3-4 days to arrive.    The sealers are also part of a three stage process, which adds time.   I went with the KBS Gold Tank sealer, primarily because I could buy the parts individually and they had the sizes I wanted.   The POR15 product required me to buy an entire kit for over $200.   The first stage is a strong degreaser that I already have.   Then there is the rust converter, then finally the sealer.

I bought the KBS Gold rust converter and then the sealer.   While I waited for the new products to arrive, I used the degreaser.  The tank was already pretty clean but it did seem a little cleaner after that process.

The rust converter and KBS Gold coating arrived yesterday, so after my kids went to bed, I went down to start the process.  The first step was the rust converter.  Since most of the rust was in the bottom of the tank, I needed a way to make sure it did not run out of the drain hole.  I took the old fuel strainer and broke off the mesh part, and then used a bolt, washer and nut to turn it into a makeshift cap.   I also used a wire cleaning brush to mostly block the return line.

The instructions called for a minimum of 20 minutes using the rust converter, moving the solution around every 5 minutes.  I ended up doing about 35 minutes and while the tank was fairly clean, I got some minor rust debris out once I removed my makeshift plug.

Once the solution had drained, the tank had to be washed out a few times and then fully dried.   Washing it out was fairly easy, but drying was a slow process.   It took about an hour using the small 18v blower I use to dry the car after a wash.  I stopped every 10 minutes or so to peer into the tank with a torch to see where I had to direct the air.   I also used a paper towel that I rolled up long and thin to dry the low area around the strainer opening.

It took about an hour to get the tank dried out.

Next step was to start the process of coating the tank.   I put my makeshift plug back in the hole for the strainer and made a funnel out of an old coke bottle.   I wish I had put gloves on at this point.  My hands are still covered in the paint.

Basically the process is that you’re supposed to coat the insides of the tank by rotating it around to get an even coverage.  Than after about 30 minutes drain the excess.   I coated the bottom and the sides, but didn’t want to clog the breather, so didn’t coat the top.   I was left with maybe 100mls in the bottom which took an eternity to drain out.  The drain hole has a lip around it.   After a lot of rotating the tank, I got about 90% of it out.  I then tried to angle the rest so it dried into the seam of the tank.    The whole process took about an hour and a half.

I now need to leave the KBS Gold sealer to cure for 96 hours.   That means I can refill the tank over the weekend.   I also suspect I may have an 80 liter tank instead of the 65 liter tank the car came from.   I’ve had a look at pictures of the tanks online.  The 65 liter tank seems to have a different shape.   I’ll be able to measure it when I refill it later.