Cleaned Fuel Tank, Petcock, and Changed Front Brake Fluid

Mileage: 27,945

Today’s Maintenance:

  • Cleaned inside of tank
  • Cleaned fuel petcock, replaced bowel seal
  • Changed front brake fluid (DOT4)

The task I’ve been dreading is done.  The fuel tank is now clean.

There are many techniques for cleaning tanks: toilet bowel cleaner (hydrochloric acid), phosphoric acid, oxalic acid, vinegar and even coke or molasseses.  You can also use electrolysis, or throw the tank filled with sharp objects into a sleeping bag and then into the dryer.  I chose to use oxalic acid because, like phosphoric acid, it leaves a coating which helps prevent rust.   I would have used phosphoric acid, but I already had some oxalic acid available.  Oxalic acid also doesn’t affect the paint.

I started the task by shaking the tank with some kerosene and a length of swing-set chain inside.  The kerosene came out brown, so I did some good with that. I wasn’t expecting this to clean the tank, I just wanted to knock of any big stuff first.

After the kerosene I degreased the tank with Dawn detergent and water.

Next came the oxalic acid.  I used two cups of powder in 4.6 gallons of hot water.  The tank was pretty clean after six hours of soaking, but I decided to let it go overnight, so twenty hours total.  I then flushed the tank several times with water, then water with baking soda to neutralize any remaining acid, then more water.

The last step before filling with gasoline was to slosh around about one-half gallon of denatured alcohol to get any last moisture out of the tank.

The red stuff you see around the filler neck in the before picture is what’s left of an old tank coating.  I cleaned that off with acetone and a cotton swab.  There’s still a bit in the bottom of the tank which I didn’t try to remove.

I discovered why the red coating was in the tank.  You can see where the red coating has sealed some small perforations on the front, lower-left corner of the tank.  This picture was taken several hours after I cleaned the tank and filled it with gas.  It doesn’t appear to be leaking, but I’ll be keeping an eye on it.

Upon inspection the petcock bowel screen and gasket didn’t look that good, especially the gasket as you can see in the picture below.   You can’t buy the filter any more, so I ordered what looked to be a whole new petcock off eBay for $8 with shipping.  I could use it, it fits, but as you can see the new petcock on the left has shorter pickup tubes, so less reserve capacity.

The new part doesn’t have a bowel filter, so I decided to steal the gasket from the new petcock and reinstall the old petcock.   I’ll try and find a gasket so I can have the new one as a backup.  Unfortunately the pickup tubes are not interchangeable.

Last task for today was to change the front brake fluid.  I ran a lot of DOT4 fluid through the system to flush it.  The old fluid looked clean, but it was slightly darker in color than the new, so it was time.  The master cylinder was, and is, in very good condition.  Brake feels good.