126 fuel tank question.
 

I do not want to change the tank on an 85 SE even though I'm replacing the gas engine with a diesel. I've consider the many years it has set with ethanol and know it's dried and consider that the diesel will eventually dissolve the residue.

I've speculated on pouring something in there to dissolve some or most of the amber type buildup left when ethanol dries but I'm concerned that some of the solvents may damage the diesel engine.

Is there a practical way to remove some of the buildup while the tank is in the car without risking damage to the diesel?

Most diesel fuel around here contains 10-15% biodiesel. Unless there is a large amount, I would think that would clean the residue left behind.

Paint (not lacquer) thinner works decent and won't affect the lines.

If the existing electric pump is still operable, dump in a couple of gallons and create a loop using the existing fuel lines. Don't include the fuel distributor in the loop.

Let the thinner set for an hour or so, jumper the relay and let the pump run for an hour or so. Undo the return line, connect a hose and feed it into a bucket, energize the pump. Use a fine mesh strainer (think automotive paint funnel) to catch debris.

You can re-use the mix if it isn't too nasty until most of the crap is gone.

Pour in fresh thinner/mineral spirits, lather, rinse, repeat.

Plan on replacing the filter 2 or three times in the first thousand miles or less.

My experience is with 2 cars. W201 and W126. I swapped the gas engines for diesel engines. I never did anything to the tanks. I just drained the gas. Filled with diesel and drove. I never needed to change a fuel filter. Common sense would tell you to have a spare filter in the car, but I never needed it. YMMV

I think I'll skip the elaborate methods and let diesel do the trick. I change fuel filters with oil at 3000-4000 miles so a few filter changes won't bother me at all. I probably have half a dozen of each waiting in storage.

Thank you, gentlemen. I'm ready to snatch the gas engine and continue this process and just trying to get a feel for some of the new obstacles I'll face.