Incorrect mpg

[Ciderbarrel]

Oh crap, yeah I totally missed that last full fill up in his post. That changes EVERYTHING. Ignore my last post because that is way off since I missed that last fill statement. I'm sorry I missed that.

Russ's example still doesn't jive because a 10L partial and a 20L partial won't equal a 30L because of the used fuel between 1st full tank and the last full tank.

The 50L for the first tank and the 30L for the last are valid. 10L of fuel was used because that 1st partial will ALWAYS be less than what was actually used, so 90L out of some X number of fuel was used.

Some more driving was done and some more fuel was burned and 20L was put back into the tank. Was 20L of fuel actually used? That is the point I'm trying to make. A partial after a partial doesn't tell you how much fuel was used, only bought. It isn't going to be as simple as Russ's example where his math somehow works out where his next full tank EXACTLY adds up to the last two partials.

Simple logic will tell you that putting in 10L and not hitting full and then 20L more and not hitting full means that the next full tank will take MORE than 30L because between the two partial fills he used MORE than 30L.

I hope I'm not over complicating things but here is another stupid example from me: a 100L tank (to keep the math simple.

Tank was full after the 50L fill, so there is 100L in it.

Some driving done, 10L put back in, not full. For arguments sake, lets say it has 99L in it. That would be a best case scenario. 10L bought, 11L used

Some more driving done, 20L put back into it. Again, let us assume that it is back up to 99L. 30L bought, 32L used.

Buying 30L can not get it back up to 100L. That is my point.

Also, if we want to avoid all this guessing, just top off your tank. I know in the UK the gas is way more expensive than here in the States, but it is the best way to be as accurate as possible.