I gave a fellow I know at the Local University a ring to try and make a little more sense out of this.

He asked a colleague, a lecturer in Fluid Dynamics, to give me a ring.

It was explained that what I had basically done was to float a layer of Petrol (2 Gallons) on top of the Diesel(12-13 Gallons) that was already in the tank.

Mixing would occur at the boundary layer between the two fluids.
If I had acted quickly, without moving the car, I could have, theoretically, pumped the Top Half of the tank contents off by going into through the filler cap. (Repeat theoretically)

As soon as the car started vibrating, through the engine being started, and the car being driven even the short distance to my home it is quite possible that intrusions of neat Petrol would start existing in the Diesel.

Think of it as water globules in oil.

Because the Specific Gravity of Diesel and Petrol are not very different (about 8%) these Globules will soon start to exist at all vertical levels of the tank.

Sooner or later , probably sooner if you allow for Sods (Murphys) Law, the pump will pick up a slug of neat Petrol -- and the rest will be history.


Apparently if you want to mix two liquids with similar, but not the same Specific Gravity, start with the item with the lowest SG and flood the higher SG liquid on top.
(Petrol first then the Diesel)

Even this is not foolproof as the colder it is the more problematical mixing becomes.

He certainly thinks I made the best decision to flush the lot.

Mike