Gas mileage versus distance driven

Yup.

 

It's variable due to a number of factors - I suspect a 19 mile drive has little to do with it - maybe the first kilometre or 2.

What is the traffic density? Speed? Traffic lights or not? Topography? State of charge? You could also be more relaxed too in the later part of the journey. All these, and more are likely to have more to do with your mileage.

What's your reverse journey like?

 

my gen2 used to warm up fine on my 14 mile commute, maybe after 1-3 miles in winter. i would average 50mpg or so on 5 miles of back roads and 2 miles at 55mph

 

At 50 degrees, were you running the heater? In my experience that is a very big drag on mileage, and especially affects warmup when using car first thing in the morning. But maybe not a factor if your car sits in a garage overnight.

I could also argue that the car was warmed up after 5 miles since at that point it pretty quickly went from 42 to 50 (ie: it averaged well over 50 between miles 5 and 10)

Only time I notice a 'warmup' issue is when it is cold out.

 

What you observed was the mathematical effect of amortizing the fuel burn needed to warm up the engine block / coolant / catalyst, first over just a few miles, and then over ever-increasing numbers of miles. The more miles you can spread out this cold-start penalty, the less it drags down your final MPG.

The best way to determine when the engine is warmed up is to watch its coolant temperature. For this, use any aftermarket OBDII-port engine monitor. I use an archaic ScanGauge-II, but there are many other products available.

P.S. Here is a spreadsheet result of your MPG for each segment of that trip. Accuracy is limited by whatever rounding you did, but I'd say that your engine was already adequately warmed up for great MPG even for the whole segment between 5 and 10 miles. I.e. it was already warmed at 5 miles, but you still needed to spread that cold-start penalty over additional miles before seeing a good total-trip MPG.

 

More-or-less off-topic rant, but anyhoo:

It used to be ANY car that rolled off an assembly line had a bonafide coolant temp gauge.

 

My last 2 didn't.

 

My first Prius was my first car with no temperature gauge.

But while my '97 Subaru had what looked like a temperature gauge, a ScanGauge revealed that it wasn't bonafide. The entire temperature span from 145F (or less) to 200-something+ was collapsed to a single point. It otherwise revealed only very low or very high conditions. Apparently that was another element of "customer expectation management".

 

The FORD mechanic said to me that they dropped them (FIESTA) because "the average driver doesn't look at them till it's too late" so the computer will 1) flash red lights; and if no attention paid, 2) turn the engine off or limp mode - he wasn't sure.

 

I.e. the same reason BMW abolished engine oil dipsticks. At least for a while, though I remember hearing of it returning on one model.

... and in the same vein, we now have drivers upset when they discover their cars don't have a flashing red light for low oil.

 

I don't recall a light for low oil - just catastrophic oil pressure. But I did have an oil temperature gauge on a VW Air-cooled engine.

 

Interesting stats