Interesting fuel octain discrepancy I found.

[Kiwicol]

Hmmm, I'm wondering if the separation you saw was ethanol separating from the petrol?

We don't have Ethanol in our petrol here, so I have no first hand accounts of it, but I do run a boat with a built in tank and that fuel goes through a water separator, water sinks to the bottom of the filter where a tap can be opened and allows the water to drain out.

 

[steve59]

pretty sure it was b4 ethanol, hell might even been b4 local stations carried diesel! I was working at the gas station back in the mid 70's when we still had to measure the fuel sold at shift change to help balance the cash (discourage stealing) and we were taught to disregard the discoloration floating above the fuel.

 

[Kiwicol]

Ahh, the plot thickens. Now we have to ask ourselves, what floats on petrol and doesn't mix easily. I know not, so I'll ask AI and see what they reckon it was.

Some of the clever cookies on here may be able to tell us why vapours leave a mark on a dipstick, but that's the reason apparently.