Hi @kezo
Many thanks for that. If I understand all of that correctly I think your car is behaving broadly the same as mine. I’ve done a number of other journeys recently and now have a clear idea of what happens when. Most of my journeys fall into two types. Let’s call them local and further afield. With both types of journey I leave with a fully charged battery, which usually states 38 or 39 miles EV range, although after the first mile (leaving our village) this has usually dropped to 35 miles.
Local round trips – these are usually in the 25 to 30 mile range. Consequently I put the car into EV mode and am able to make the whole journey on electric. This results in a cost per mile that’s effectively half of what I was paying with the BMW.
Further afield trips – I make a 56 mile round trip every week or so and every few weeks do a 104 mile trip. 90% of these journeys are on the M5 motorway. I have tried the trips in ‘Auto’ mode and ‘HEV’ mode but, crucially, where I differ from you is that I always use cruise control. Speeds vary between 60mph and 80mph. The two modes behave very differently on the same journey;
Auto Mode – The car tends to be in EV from the start and for the first 10 miles or so. Then the engine will kick in for periods on the motorway, during which time it will periodically go into what you call ‘charge’ mode, when the engine is both propelling the car and charging the battery. It only does this for short bursts though, usually adding around 2 miles to the EV range and then deploying it. When I leave the motorway it mostly reverts to EV mode and when I get to my destination I still have 20-25 miles EV range to use on the return journey.
HEV mode – The engine comes on much sooner and stays on much longer. When I’m on the motorway it’s mostly in charge mode, where it propels the car and charges the battery. However, unlike in Auto mode, it will keep doing this until the battery is fully charged. During this time, consumption is around 20 mpg (as I’m sure you know, the little triangle is average mpg not instant). Now I appreciate that this 20 mpg is only half the story, because it’s also ‘buying’ you EV mileage, but even if it’s buying you one mile EV usage for every one mile in HEV mode that’s still only around 40 mpg. I would have easily bettered that in the petrol BMW.
As a result of experimenting over several identical journeys, I now always use Auto rather than HEV mode on longer journeys. I haven’t filled up with petrol a second time yet, so haven’t got any confirmed figures, but I did a back of a fag packet calculation on a recent 104 mile trip, leaving with a full charge;
Outward mpg in Auto mode (52 miles) showed on the computer as 47.6mpg. This was with part of the journey being in EV and some of it in the fuel inefficient charge mode.
The return journey, also in Auto mode (same 52 miles) was showing as 87.6mpg. This was because I forced the car to use up all remaining battery power and the engine only kicked in for the latter part of the journey, when it did some self charging.
This means the average for the whole trip (as per the car computer) was 67.6mpg. Now, as we know that mpg stated in PHEVs is incorrect as it doesn’t factor in the cost of the charge, I did the following calculations;
104 miles at 67.6 mpg equals 1.54 gallons which equalled £9.52 petrol cost. Add to this the £2.60 that it cost me to charge the car and the total cost was actually £12.12 or 11.65p per mile. Dividing that price per mile into the cost of petrol alone gives the true mpg equivalent (if all expenditure had been on petrol) of 53mpg – some 14.6mpg worse than the incorrect figure stated in the car. However, this was probably around 5mpg better than I’d have got from the BMW over the same journey, so I was OK with that.
I’ll get a much more accurate picture when I next refuel in a week or two, as that will cover quite a lot of journeys and a lot of charges, so I will then be doing the same calculations and comparing the result to my long term average of the BMW (42.2mpg).
Finally, can I just clarify what you mean by “Engine Fuel Mode”, where the engine only powered the car but didn’t recharge the battery. I’d like to be able to force the car into that behaviour when the battery is depleted but cannot see a way to do it. Am I missing something?