2010 Avensis T27 Fuel economy not good

[MikeEH]

The spec for the 2010 Avensis 1.8 T27 is 41 to 42mpg. I cannot get over 30.7mpg. The only comparison I have is my old 1.8 T25 which gave me 34 to 38mpg locally and up to 49.9mpg on motorways. In my T27 I initially got 30.5mpg locally (due to lockdown, etc), and after travelling 25 miles on a motorway for the jab, it increased to 30.7mpg. It has now stuck on 30.7 driving locally. I have reset the display on 3 occasions, but keep getting the same readings and even though I'm not doing the mileage that I used to, I seem to be filling up much more than I did in the T25.  I can't seem to achieve the 41 to 42mpg spec. Is there anyone else out there with a T27 who can let me know their mpg as a comparison please?

[nielshm]

Can you smell unburned fuel when the car is running?

With MPG this bad, it's likely a lambda sensor or something that sets the fuel/air mixture may be broken.

 

[Konrad C]

At the moment my car is averaging just over 34 mpg with mixed local driving. I live South East London/Kent, so the roads range from 20 mph (some with speed humps), 30 mph roads - my borough Bexley is not like some other London boroughs with blanket 20 mph on most roads. There are 40 and 50 mph roads local to me too. I live at the bottom of a hill, so a lot of ascending involved too. 
I checked the tyres and they needed some air. Also it had been cold so used air-con to demist interior windows. When windows are icy, I clear them before even starting the engine. I then drive straight away. Only if the interior windows need clearing, that I turn the engine on to clear, whilst clearing the outside glass. Oh yes, I am using 0w-20 fully synthetic engine oil, which is lighter. Also check the air-filter and I think about the spark plug. I use Denso Iridium.

All this can add to higher fuel consumption. 

I have seen a lot of newer cars with smaller petrol turbo engines, and they have worse fuel consumption. These are the Ford 1.0L Ecoboost, and the Vauxhall 1.4 turbo. I have seen low 20's to low 30's. Even Mercedes A Class smaller petrol turbo can have a poor economy!

[MikeEH]

Thanks for replies.

I don't smell unburned fuel when the car is running. Everything seems normal. If a sensor is broken wouldn't it show up on the dash display?

I live half way up a mountain but don't accelerate up it, I just drive normally as I did in my T25. Tyre air pressure is constantly checked, and the air filter is new-ish. Can't remember what oil I'm using but it was one recommended in the handbook. I only bought the car in December 2019 and it was alleged to have had a service and MOT prior to my purchase. I've only done 3K miles since due to Covid lockdowns, etc., hence the air filter is 'nearly new' - been checked. Maybe the plugs should be examined for new-ness and maybe replaced. I always use NGK Iridium plugs. What were the Denso plugs that you use Konrad?

[Konrad C]

Hi Michael, I am currently using Denso Iridium SC20HR11 spark plugs. These are no longer available, superseded by SC16HR11. So if and when I need to replace the spark plugs, I will see what is available. 

Look at the following link:-   https://www.denso-am.eu/media/corporate-news/2017/june-2017-product-bulletin-supersessions-within-the-spark-plug-range/

[TonyHSD]

If the car been only used short town trips plus the cold weather it’s normal to worsen its fuel efficiency, however if lambda sensor front fuel-air ratio sensor is dirty or faulty the car will have rich fuel mixture, may have sometimes rough idle and will burn mote fuel. Black soot in exhaust pipe end, and black spark plugs are common sign of it, or even slightly black smoke when pushed harder , something that you might not be able to notice. Check the plugs if they are black , you need to check the lambda sensors that stays before catalytic converter and eventually replace, or clean. Plugs can do too, this picture shows plugs from car with rich fuel mixture most likely faulty or dirty lambda sensor,. 👍