How PHEV mpg is calculated

[jeffgolding]

Hi,
I am a new member, picking up my HS PHEV on Tuesday. One thing that confuses me is how is the mpg is worked out, is the electric charge taken into account?
What I mean is if I start of with a full charge and use that all up, then it switches to ICE petrol and I do say 90 miles total that would be 32 on EV MODE and 58 using petrol, how would it calculate my combined MPG ?
Thanks for any clarification you can offer,
Jeff

 

[N2STY]

I think if your battery is flat you mpg is like a normal car the mpg is worked out on a combination of engine and battery usage so you aim to get home with a flat battery to get the most out of it

 

[MG273]

It’s simply distance travelled over fuel used. When the engine is off no fuel gets used and the mpg climbs up.

 

[jeffgolding]

I think you misunderstand me, if the vehicle is using battery power, that is at a cost.
so if you drive 100 miles on combined battery till it’s flat, and petrol and the mpg is shown as 100MPG, that is not true because 32 were driven on electricity and that is a cost that should be included when calculating MPG.
Or am I being thick

 

[C6MFC]

In the first two weeks I only used EV mode (twice ICE used for short demist on damp morning) The accumulated trip page was showing over 200 mpg. I did a Hybrid trip on Sat around 80 miles and the accumulated MPG came down to 85 mpg as you would expect. Interestingly the visual showed battery assisting the ICE a lot but the Electric GOM only came down to 27 miles. Is there an optimal setting for Hybrid driving or is it fully automatic.

 

[a1970man]

I think you misunderstand me, if the vehicle is using battery power, that is at a cost.
so if you drive 100 miles on combined battery till it’s flat, and petrol and the mpg is shown as 100MPG, that is not true because 32 were driven on electricity and that is a cost that should be included when calculating MPG.
Or am I being thick

I take your point, but you're asking what is the MPG (Miles per Gallon, of fuel).
If you do 100 miles and use 1 gallon of fuel, but the first 32 on EV, you are doing 100 MPG as you have expended 1 gallon of fuel but covered 100 miles.

That's how I'm looking at it anyway.

 

[MG273]

I think you misunderstand me, if the vehicle is using battery power, that is at a cost.
so if you drive 100 miles on combined battery till it’s flat, and petrol and the mpg is shown as 100MPG, that is not true because 32 were driven on electricity and that is a cost that should be included when calculating MPG.
Or am I being thick

Haha you said it..
It’s not a cost calculation, it’s efficiency. It’s referring to gallons of fuel.
If you wanted a cost calculation the car would have to know how much you have paid for fuel per gallon and electricity per kWh, or you could just work it out yourself if you were that interested.

 

[jeffgolding]

Thank you all, so basically it is a waste of time showing mpg, as it includes electricity used too. Therefore in a perfect world should only be registered when the ICE IS USED.

 

[MG273]

Thank you all, so basically it is a waste of time showing mpg, as it includes electricity used too. Therefore in a perfect world should only be registered when the ICE IS USED.

I wouldn’t call it a waste of time, it’s basically just a way of seeing how much more fuel efficient your car is due to fact it’s a hybrid.

 

[jem111111]

Take a look at the post " Considering buying the HS Phev but need some advice" as there is some good information on there re use in winter and economy

 

[sky0000547]

Thank you all, so basically it is a waste of time showing mpg, as it includes electricity used too. Therefore in a perfect world should only be registered when the ICE IS USED.

People have asked what is the MPG on the PHEV and I have often answered it can be anything. It can be as high as you want to infinity or it can be low in the 30s and 40s. If someone continuously charge and just drive in EV, literally you can have infinite MPG.

 

[neilp7865]

Agree with sentiments above. It’s somewhat outdated and I don’t think it’s really accurate. What’s more meaningful is the electric range and then the petrol mpg from there. My PHEV (non MG) does c35 miles on battery then usually around 45mpg. Blended average of mpg is kind of meaningless.

 

[Davecv]

Hi I have been driving my MG PHEV duing the winter and a bit frustrated with the Engine requiremnt for the heater cutting off the EV completely. Our Kia Niro uses the battery for traction and seems to idle the engine to provide heat. Does amazing MPG. I have been keeping a log of petrol use over the winter. I switch the car over to EV as soon as I think the demands of the heating are met. This is usually after 2 miles or so. My impression is that I am doing a lot of EV miles. I have logged the car for 2766 miles and I calculate overall 41.8mpg , the display on the car has logged 3650 miles and is showing 43mpg. This is NOT very good. The fuel guage shows miles available in petrol terms and I have tried to log this as well so miles used acording to the guage taken away from miles on the car might aproximate to EV miles. This would make the petrol engine alone at 32mpg which is dismal. The PHEV despite my efforts is doing no better than a normal MG-HS. This maybe that during the winter I am nonly running the engine until it warms up which is not going to be efficient. Perhaps when using the heater is is better to run the engine up to temp and let the battery run STOP/START. Hoping for better in the summer.

 

[Davecv]

AND ALSO - if the car had an electrically heated fron screen for de-misting I would probably sit in the cold and run EV during the winters short journeys.

 

[Deleted member 3150]

Hi I have been driving my MG PHEV duing the winter and a bit frustrated with the Engine requiremnt for the heater cutting off the EV completely. Our Kia Niro uses the battery for traction and seems to idle the engine to provide heat. Does amazing MPG. I have been keeping a log of petrol use over the winter. I switch the car over to EV as soon as I think the demands of the heating are met. This is usually after 2 miles or so. My impression is that I am doing a lot of EV miles. I have logged the car for 2766 miles and I calculate overall 41.8mpg , the display on the car has logged 3650 miles and is showing 43mpg. This is NOT very good. The fuel guage shows miles available in petrol terms and I have tried to log this as well so miles used acording to the guage taken away from miles on the car might aproximate to EV miles. This would make the petrol engine alone at 32mpg which is dismal. The PHEV despite my efforts is doing no better than a normal MG-HS. This maybe that during the winter I am nonly running the engine until it warms up which is not going to be efficient. Perhaps when using the heater is is better to run the engine up to temp and let the battery run STOP/START. Hoping for better in the summer.

I’ve done over 6000 miles since last July and show on my trip which has never been rest 86 mpg. I do mostly round trips of less than 32 miles and when on long journies do agree with you opinion of the petrol engine, old unrefined, not economical, burns through the battery very quickly in hybrid mode meaning running without much battery support. Using the 2 battery regin modes seems to use more petrol than battery saved unless on a long motorway trip between towns

 

[jeffgolding]

I take your point, but you're asking what is the MPG (Miles per Gallon, of fuel).
If you do 100 miles and use 1 gallon of fuel, but the first 32 on EV, you are doing 100 MPG as you have expended 1 gallon of fuel but covered 100 miles.

That's how I'm looking at it anyway.

But surely the electric must be taken into account ie, 32 miles on ev equivalent of 3.5 ltrs of petrol therefore 1.77 gallons for 100 miles = 56.4 mpg.

 

[Vipar]

Full battery. Full tank fuel

Run car until battery flat go home record mileage

charge battery note the cost

fill up with fuel note cost

add the 2 costs together divide the cost into the mileage that will give you cost per mile.

other than that walk around the car 3 times and admire it as it will be a lot cheaper that an ice car.

to me its not MPG that counts it's journey cost.

 

[jem111111]

But surely the electric must be taken into account ie, 32 miles on ev equivalent of 3.5 ltrs of petrol therefore 1.77 gallons for 100 miles = 56.4 mpg.

Hi Jeff , that all depends on the cost of your electric.
If i charge the car at night and use octopus go faster its 5.5p per kw. This will be increasing soon to 7.5p per kw. If my memory serves me right , the PHEV has approx 13kw of usage battery for the 32 miles ( i know i get more than this range but lets say it 32)
So at 5.5p ( x13) = 71.5 p for 32 miles. ( 2.2p a mile)

At the 7.5p rate that goes up to 97.5p ( 3 p a mile)

At 30p rate that goes up to £3.90 ( 12p a mile)

A gallon of petrol is 1.68 per litre ( x 4.5 for a gallon) = £7.56
At these prices
If you car does 30mpg ( 25p a mile)
If your car does 40 mpg ( 19p a mile)
If your car does 50 mpg ( 15p a mile)

So in theory for a price of a gallon , how many full charges can i get at my electricity rate
so £7.56 / 71.5 p = 10.5
so in theory if i do not drive over 32 miles in any given trip then32 x 10.5 will give me the amount of ev milage i can do for the equivalent of a gallon of petrol = 338 miles

If i do it for the soon to be higher charge its £7.56 / 97.5p = 7.7
So again 32 x 7.7 = 248 equivalent miles

If i do it for the 30p rate £7.56/ 3.9 = 1.93
So again 32 x 1.9 = 62 equivalent miles.

Again in real world conditions its a hybrid , so at some stage you will use the engine ( put the heating on , drive for more than 32 miles etc) , but the more you just use the EV mode ( by manually switching to it ) the cheaper it will get.

I mentioned before ( on another thread) in January.
I posted one when i first got it and went down the route of trying to cost out ( pence per mile) the phev against an ICE car. It was good to do , but i remember Greebo12 saying i was over complicating things and to just see how much petrol you put in. I must admit i did not quite see that point of view at the time , and its just now after knowing more about the car and how to run it , i can see what they meant.
So for example we filled up the tank a couple of weeks just before the dreaded UK petrol shortage happened in September in the UK ( how lucky was that ).
Just before christmas we filled it up again ( even though there was 50 odd miles left) so thats 2 tanks.

We have added a 3rd tank of petrol since my reply in January so thats 3 tanks in 6 months ( which isnt too bad ) the rest of the time we just charged it overnight ( on cheap octopus go ) and used it in EV mode.
I hope that helps

 

[jeffgolding]

Hi Jeff , that all depends on the cost of your electric.
If i charge the car at night and use octopus go faster its 5.5p per kw. This will be increasing soon to 7.5p per kw. If my memory serves me right , the PHEV has approx 13kw of usage battery for the 32 miles ( i know i get more than this range but lets say it 32)
So at 5.5p ( x13) = 71.5 p for 32 miles. ( 2.2p a mile)

At the 7.5p rate that goes up to 97.5p ( 3 p a mile)

At 30p rate that goes up to £3.90 ( 12p a mile)

A gallon of petrol is 1.68 per litre ( x 4.5 for a gallon) = £7.56
At these prices
If you car does 30mpg ( 25p a mile)
If your car does 40 mpg ( 19p a mile)
If your car does 50 mpg ( 15p a mile)

So in theory for a price of a gallon , how many full charges can i get at my electricity rate
so £7.56 / 71.5 p = 10.5
so in theory if i do not drive over 32 miles in any given trip then32 x 10.5 will give me the amount of ev milage i can do for the equivalent of a gallon of petrol = 338 miles

If i do it for the soon to be higher charge its £7.56 / 97.5p = 7.7
So again 32 x 7.7 = 248 equivalent miles

If i do it for the 30p rate £7.56/ 3.9 = 1.93
So again 32 x 1.9 = 62 equivalent miles.

Again in real world conditions its a hybrid , so at some stage you will use the engine ( put the heating on , drive for more than 32 miles etc) , but the more you just use the EV mode ( by manually switching to it ) the cheaper it will get.

I mentioned before ( on another thread) in January.
I posted one when i first got it and went down the route of trying to cost out ( pence per mile) the phev against an ICE car. It was good to do , but i remember Greebo12 saying i was over complicating things and to just see how much petrol you put in. I must admit i did not quite see that point of view at the time , and its just now after knowing more about the car and how to run it , i can see what they meant.
So for example we filled up the tank a couple of weeks just before the dreaded UK petrol shortage happened in September in the UK ( how lucky was that ).
Just before christmas we filled it up again ( even though there was 50 odd miles left) so thats 2 tanks.

We have added a 3rd tank of petrol since my reply in January so thats 3 tanks in 6 months ( which isnt too bad ) the rest of the time we just charged it overnight ( on cheap octopus go ) and used it in EV mode.
I hope that helps

Thanks for that, I understand. It was in my thoughts because loads of people say they get fantastic mpg, but they don’t take the electric into account. To be honest if I get 50-60 mpg I will be very happy. So using your maths I am on EDF 98 tariff which gives me 10 hours a day and all day sat and Sunday at 15p per kWh so it equates to 124 mpg on ev, so I’m happy with that. Going to Yarmouth for a week so I will be running mostly on petrol there and back and ev when I am running around up there, so that will be interesting. Thanks for your help. Jeff.

 

[jem111111]

Hi Jeff glad it helps. When I have been on holiday in it ( long journeys), i got about 40 mpg. That's not too bad for such a big car .
My thoughts are , I don't mind the not so good mpg when doing longer journeys ( over 90 miles) as that's only done about 10 times a year. The rest is then mainly on EV , which at 2 p a mile is great.
Why didn't I then go full EV ? Simple answer , charger anxiety lol. Not many chargers in Wales , Cornwall , Northumberland etc where we like to go. I would rather have a hit on the petrol mpg , but have less stress when driving on the long journeys.