1978 6.9 fuel tank cleaning
 

Hello all,
Trying to find the correct forum for this topic.
I have been working, this week, on the fuel system of my 1978 6.9.

The fuel tank is removed and I am puzzled about a few things.

First is that the fuel sending unit has no wiring harness. (No wonder the gauge is not working) Can not understand what would cause someone to remove it?

Second question is about the swirl pot. The top is not on the pot, it is just rattling around inside the tank. How do I get the top back on?

Third question has to do with the cleaning process. I have blasted the tank at the car wash and then at home repeatedly. Used CLR and then washed with kerosene twice and let sit overnight with kerosene then blasted with water again a few times today. It is now sun bathing with an occasional blast of air.
What is the consensus on pour in tank liner? And do you have any other advise on what I should do before reinstalling the tank?

Also I have a fiberglass reserve tank that was made for a Mercedes that I hope to install. It fits nicely in the trunk with a nice angle back to allow for luggage.
Is there a prescribed method to plumb the tank into the main tank?

Thanks in advance for your time and help.
Edit/Delete Message Reply With Quote Multi-Quote This Message Quick reply to this message

I've used acid to clean tanks with success but I think your car wash approach is just fine as long as the tank is not already rusty. I'm not sure if you should use a liner as it may block some breather lines and create problems down the line. If there are no flaking rust bits, then I'd leave it at that.

No comment on the reserve tank.

Thanks for the reply.
There was a lot of chunks and flakes that just kept coming. Overall it looks good but there are flakes of rust on the roof of the tank along the lines. People have said that the flakes are not rust that they are in fact varnish from the old fuel.

Your pressure washer should have blasted those away and now the metal inside (if you shine a flash light through the strainer and the sender) should show clean metal.

The 6.9 is of course a special car, but I would think the gas tank would be the same on all gas 116 cars.

Perhaps you could hit a few wrecking yards and see if you can come up with a good one.

I once did a lot of work on a friends 1976 Ford Van with dual tanks and one of the tanks was like new and the other was rusted and full of scale. I mean it was scary looking scale. I recommend he replace it but he just cleaned it up and put it back in.

Then he filled both tanks. Everything was fine until he switched to the 'cleaned' tank and then his fuel filter clogged up solid.

He finally hit the junk yards and found a new tank.

Someone on this board likely has a 116 they are parting out, and while shipping may cost $$$$ it just might be worth it in the long run.

And since this is a 6.9 you might want to check out The International M-100 Group which is the site of the M-100 club. I once owned a 6.3 and the members there were able to provide a great deal of help concerning this unique autos.

M100 group
 

I have joined and posted on the M100 Group but I guess they do not have a large number of members so I posted here as well since I am in the middle of this process and doing it for the first time.
I have been helped so much by this forum over the years that I feel more at home here.
I do have another W116 that has become a parts car for the 6.9 but I believe that the tank is in good condition.
Due to the fact that this is my first fuel system job, I was looking for some friendly encouragement. And I am a diesel guy so this job is complicated by the idiosyncrasies of a gasser.

electrolysis cleaning
 

After many days of soaking the fuel tank in kerosene and then blasting with water, I have decided to use the electrolysis method to remove the rust, due to the fact that all of the other methods score the metal and remove a portion of material, even from the un-rusted parts. And it is free.
The positive lead from the battery charger is attached to a piece of re-bar (sacrificial anode) and the negative lead is connected to the tank. The tank is filled with water with one tablespoon of baking soda per gallon. The end of the bar and the portion that touches the tank at the opening are wrapped with rubber.
Will report back after 24 hours time.

How to prime fuel?
 

Tank is reinstalled in the car. New tank screen, filter and hoses installed. Found the wiring harness for the sending unit and cleaned and rebuilt the sending unit, what a mess it was, totally frozen float, very dirty on the inside. Added 12 gallons of super unleaded with marine Sta-Bil.
Now I have a battery sitting on the ground wired directly to the fuel pump but no fuel is flowing. The main line to the fuel distributor is disconnected and in a jar to catch the fuel but I do not hear any noise transmitted through the line and I cannot feel air.
The question is how to prime the fuel system?

primed
 

The lines are primed. I cannot take credit, apparently sitting for 2 days primed the lines.

Now that I know there is clean fuel being delivered to the engine the real work begins.