If there is anything close to the amount of gasoline mixed with your diesel
fuel that you suspect, you will easily be able to smell it. Pull a small
sample and sniff it or first just simply take a whiff from your fuel fill .
It doesn't take much gasoline mixed with diesel for the gasoline smell to
become apparent. Obviously, this will not be scientific but it will give you
a direction to head.

--
Ron White
Boat building web address is
www.concentric.net/~knotreel