Diminishing MPG

[Michael L]

I got my Touring Sports 1.8 in April. Right through until September I was getting a steady average mpg of 68. Recently I'm struggling to beat 63 with no change in driving conditions. I'm wondering if anyone has similar experience? I would have expected it to improve as the engine runs in. I've done 6500 miles so far.  I'm not sure if Toyota would recognise it as a guarantee issue.

[forkingabout]

It's now colder, engines including Toyota hybrids use more fuel in the winter & average mpg drops. 

[Bernard Foy]

8 minutes ago, Michael L said:

I got my Touring Sports 1.8 in April. Right through until September I was getting a steady average mpg of 68. Recently I'm struggling to beat 63 with no change in driving conditions. I'm wondering if anyone has similar experience? I would have expected it to improve as the engine runs in. I've done 6500 miles so far.  I'm not sure if Toyota would recognise it as a guarantee issue.

It’s normal for the mpg to diminish by at least 10% and more as the temperatures begin to fall.

[Mojo1010]

Not having a dig, unless this is your first car ever, most will know it's to do with colder weather. See these posts pop up a fair few times recently. My Yaris hybrid drop about 15mpg in the winter. 

[AndrueC]

29 minutes ago, Mojo1010 said:

Not having a dig, unless this is your first car ever, most will know it's to do with colder weather. See these posts pop up a fair few times recently. My Yaris hybrid drop about 15mpg in the winter. 

Hybrids do seem to suffer a bigger drop though (at least to my mind).

[Roy124]

Michael, also check your tyre pressures.  I don't know how often you check but that is always a possibility. 

Even if you check regularly your cold pressure now will be less than in summer.  I don't know though whether hot tyres in winter run cooler than in summer.

Which reminds me 😁

 

[TonyHSD]

Yes, I will agree with others, it’s from the colder weather, happens every year same time. However this year there is something else that plays a role too, it’s actually since last September and it’s the E10 95 petrol. I noticed my car loose immediately 3-5mpg if I switch to E10 from E5 99. I tend to mix them recently and every time I have e10 refill the mpg goes down to around 52 from 56-58 from the previous refill with e5. Summer time there is no difference at all and sometimes even the car is slightly more efficient on e10. 
You can try E5 for yourself and see if your car will behave the same . There is no much of an improvement after some miles been traveled as these cars no need to be run in. 

[Michael L]

Thanks for all of the comments. It's not my first car of course, but it is the first one that had mpg as a principal reason for buying it. Hence the close interest in results. Also very interesting about E10.

[Cyker]

2 hours ago, AndrueC said:

Hybrids do seem to suffer a bigger drop though (at least to my mind).

You're right - Ironically the more efficient the car the worst it gets hit!

A big part of it is the engine temperature - All engines want to be hot and have terrible efficiency until they get to operating temperature.

Petrol engines tend to get hit the least as they generate a lot of waste heat so they get up to optimal temps relatively quickly, and stay there (And also make the cabin nice and warm!)

Diesels generate far less waste heat, so they take a lot longer to get up to temp, esp ones with big steel engine blocks which soak up a lot of heat, but once they're there they tend to stay there, so if you're doing a fairly long journey the mpg will still be pretty good, but if you only do lots of short journeys the mpg can be worse than a petrol! My dad once managed to get 135 miles out of a tank of diesel in his old Focus TDCI, vs the 550+ miles it should be capable of!    

The Toyota hybrids have the same problem as the diesel - Atkinson/Miller cycle means they generate less waste heat, tho' more than a diesel, so they also take ages to get to optimal temperature, but the killer is they turn off, which means they cool down again instead of staying at operating temperature. I find my Mk4 either needs to run the engine ALL the time, or I need to turn the heating off completely in winter, otherwise it never reaches operating temperature as the heater sucks heat out of the engine faster than it can make it, and even then it struggles to stay at its normal 4-blocks of heat unless I'm on the motorway.

 

[JARC1]

Is there any specific reasons why E5 should not be used and what is the reason for E10 ?

Regards, John

[Kental]

17 hours ago, JARC1 said:

Is there any specific reasons why E5 should not be used and what is the reason for E10 ?

Regards, John

E10 is cheaper

[Roy124]

Cyker, thanks for the explanation.  I had thought that but not formulated the idea.  However I asked earlier, would there be an benefit in adding a radiator muffler as many cars used in the 50s and 60s.

They were necessary because the cooling fan ran continuously and dropped out of favour when thermostatic controlled fans were introduced (using volts).  My SAAB fan would regularly start after I had switched off. 

[Yugguy1970]

I find the RAV engine stays warm longer than the Yaris one does, perhaps simply due to its bigger size.

I also think the entire hybrid system is an amazing piece of engineering and design that I wouldn't want to eff about with.

[Cyker]

4 hours ago, Roy124 said:

Cyker, thanks for the explanation.  I had thought that but not formulated the idea.  However I asked earlier, would there be an benefit in adding a radiator muffler as many cars used in the 50s and 60s.

They were necessary because the cooling fan ran continuously and dropped out of favour when thermostatic controlled fans were introduced (using volts).  My SAAB fan would regularly start after I had switched off. 

Yeah I was thinking if I should try that last year but never got around to cutting up some cardboard/to-let sign to the right shape.

Theoretically it shouldn't be needed since the coolant shouldn't get pumped round the engine until it gets warm enough, but I think just the air blowing over the engine is enough to sap the heat away.

 

3 hours ago, Yugguy1970 said:

I find the RAV engine stays warm longer than the Yaris one does, perhaps simply due to its bigger size.

I also think the entire hybrid system is an amazing piece of engineering and design that I wouldn't want to eff about with.

That's the advantage of a bigger engine - less surface area to mass, so the heat can 'hide' away from the air flow a bit better. The M15A in the Yaris Mk4 is tiny and is extremely light so it has too much surface area compared to its thermal mass to stay hot when the ambient temperature is low, esp. if the cabin heating is on, but can warm up faster if the engine is running under load.

A funny bit of trivia - The original Prius had an insulated coolant reservoir it would pump hot coolant into when the car was turned off, and when it was turned on again that coolant would get pumped back out to heat up the engine without needing to waste fuel to do so.

I thought this was genius, but I guess it didn't work very well since they removed it from all later versions of the hybrid system. Toyota like to remove things if there's not enough benefit from them, but I feel the Mk4 would have benefited from something like that!

 

[Mojo1010]

I would think it's the size of the RAV4 engine too. I have the smallest hybrid in the range, MK3 Yaris, it's a great car for city driving, cannot knock it at all. What it lacks for me is when it comes to regular medium distance driving. 

I have good information the mk4 Yaris has changed all of that, more capable for doing those distances, also a vast improvement. So looking forward to get my hands on that next year. 

[TonyHSD]

All Toyota hybrids loose engine temperature quickly for two reasons; 

1. The engine doesn’t work all the time 

2. Light load when engine is working 

The only time you are not loosing heat is when travelling on motorway with sleds of 60+ mph, then the engine is more loaded and can handle the heat and to provide better for cabin heating too. 

[Gerhard_Corolla]

On 11/7/2022 at 5:44 PM, TonyHSD said:

Yes, I will agree with others, it’s from the colder weather, happens every year same time. However this year there is something else that plays a role too, it’s actually since last September and it’s the E10 95 petrol. I noticed my car loose immediately 3-5mpg if I switch to E10 from E5 99. I tend to mix them recently and every time I have e10 refill the mpg goes down to around 52 from 56-58 from the previous refill with e5. Summer time there is no difference at all and sometimes even the car is slightly more efficient on e10. 
You can try E5 for yourself and see if your car will behave the same . There is no much of an improvement after some miles been traveled as these cars no need to be run in. 

In theory Gas Stations are obliged to offer both fuels, and due to Bio-ethanol's unreliable supply, more times than we think possible, E5 fuel is being pumped through the E10 nozzles...

 

 

[davidif]

On 11/7/2022 at 7:01 PM, Cyker said:

You're right - Ironically the more efficient the car the worst it gets hit!

A big part of it is the engine temperature - All engines want to be hot and have terrible efficiency until they get to operating temperature.

Petrol engines tend to get hit the least as they generate a lot of waste heat so they get up to optimal temps relatively quickly, and stay there (And also make the cabin nice and warm!)

Diesels generate far less waste heat, so they take a lot longer to get up to temp, esp ones with big steel engine blocks which soak up a lot of heat, but once they're there they tend to stay there, so if you're doing a fairly long journey the mpg will still be pretty good, but if you only do lots of short journeys the mpg can be worse than a petrol! My dad once managed to get 135 miles out of a tank of diesel in his old Focus TDCI, vs the 550+ miles it should be capable of!    

The Toyota hybrids have the same problem as the diesel - Atkinson/Miller cycle means they generate less waste heat, tho' more than a diesel, so they also take ages to get to optimal temperature, but the killer is they turn off, which means they cool down again instead of staying at operating temperature. I find my Mk4 either needs to run the engine ALL the time, or I need to turn the heating off completely in winter, otherwise it never reaches operating temperature as the heater sucks heat out of the engine faster than it can make it, and even then it struggles to stay at its normal 4-blocks of heat unless I'm on the motorway.

 

Id bet that the Battery is less efficient in cooler temperatures too which will only add to the problem!

[TonyHSD]

1 hour ago, davidif said:

Id bet that the battery is less efficient in cooler temperatures too which will only add to the problem!

True 👍

[TonyHSD]

1 hour ago, Gerhard_Corolla said:

In theory Gas Stations are obliged to offer both fuels, and due to Bio-ethanol's unreliable supply, more times than we think possible, E5 fuel is being pumped through the E10 nozzles...

 

 

It could be possible indeed, for some reason sometimes the fuel bought from the same garage , same pump delivers more power and less noise, additives or simply different amounts of ethanol, I can’t say, but I can feel it every time. 

[Roy124]

1 hour ago, Gerhard_Corolla said:

In theory Gas Stations are obliged to offer both fuels, and due to Bio-ethanol's unreliable supply, more times than we think possible, E5 fuel is being pumped through the E10 nozzles...

 

 

Not in UK supermarkets.  Several here offer only the cheaper E10. 

[Kental]

21 hours ago, Roy124 said:

Not in UK supermarkets.  Several here offer only the cheaper E10. 

The implication is that there is no E10 at the refinery so E5 would be delivered instead

[Roy124]

1 hour ago, Kental said:

The implication is that there is no E10 at the refinery so E5 would be delivered instead

I was really meaning that there was no  obligation in UK to offer E5 and evidenced that some supermarkets sold only petrol from E10 pumps. 

[Cyker]

The E number specifies the Maximum percentage of Ethanol in the fuel, but often it's less, esp. when Ethanol costs are high (Which in of itself is a sign we're not doing it right - ethanol should be cheaper than petrol!!)

It's why Esso can sell their fancy 'E5' superfuel, which actually has no ethanol in it at all, and still be compliant.

I'm not actually sure where the ethanol gets added, whether it's in the fuel or if it's added on-site like the additive package is.

[Rhymes with Paris]

Have I understood that right Cyker, that the Esso one has no ethanol at all in it ?

As I did fill up with the Esso E5 at Tesco's the other week as I couldn't be bothered driving to the other end of town for my usual Shell v power, I was wondering if it was my imagination, but it seemed to run better with slightly more power.

Mind you, they are a bit of a rough crowd filling up at the Tesco's, some of them had jogging bottoms on and face tattoos, and didn't use the plastic gloves.