sudden heavy fuel use?

sophlouwhit

maybe i am over thinking things but i have noticed a fairly drastic drop in MPG. we have a toyota yaris, 2013.

does age effect MPG? does winter effect MPG?

spark plugs are original, car done 80k

new tyres and always kept to good pressure

yearly full service

I would say overal a well maintained car

I have noticed this sudden dip in MPG, where it seems to be drinking a LOT! we used to get 45mpg average now 38mpg average (this is using milage and liters put in vs car computer which i do not trust). Not sure what to think.. does MPG decrease with age? what can we do to help it? to add we add a fuel cleaner which claims to clean injectors every 6 months, once winter and once before MOT (we never used to do this and its a new thing as of last year and hasnt especially helped MPG -2019 average compared to 2018-

AdrianC

First off, 45mpg vs 38mpg... That sounds like it's entirely possible you're working the wrong litre-to-gallon amount, especially since you used the US spelling of "liter"... Imperial gallons are 4.5 litres. US gallons are 3.8 liters. 10 miles per litre would be 38mpug and 45mpig...

Yes, winter will reduce economy, especially on shorter journeys - you're using lights/wipers more, there's more rolling resistance from wet roads, and the engine is taking longer to reach operating temperature. Modern spark plugs are much longer life than they used to be - 100k+ is not an unusual recommendation, and if it's not misfiring, they're probably fine. I presume this "full service" has changed the air filter as required, so it's not trying to breathe through a facemask? Checking the emissions would show whether the lambda and cat are still working fine.

I'm not surprised the "injector cleaner" goop hasn't done anything - they're snake-oil, and only clean your wallet.

facade

As Adrian says, you can expect 5-10% worse economy in pouring rain and very cold weather, but it might be worth checking for a binding brake- after a run one wheel feels noticeably warmer than the one on the other side (don't put your finger on the brake disc)  or getting the lambda reading checked, as oxygen sensors don't last forever.

The_Rainmaker

On cold short runs my car (diesel) will drop from 40 mpg to low 30s mpg heavy rain will also drop it by 10%.

sophlouwhit

Thanks guys. Yes the air filter was apparently replaced. I am thinking about get fuel filter replaced? Someone mentioned this to me anyway..?? Havent noticed any engine misfire. Regarding spark plugs - are NGK or Denso better? If we do decide to get replaced & someone has mentioned to.me about getting engine cleaned but not entirely sure needed or would help?

marlot

Make sure the air filter is clean.
Is the car getting up to temperature?  I don't remember a Yaris having a temperature gauge, so it would be a case of feeling the top and bottom radiator hoses to make sure the thermostat isn't jammed open.
Another possibility is a partially blocked exhaust.

AdrianC

The fuel filter should be being replaced regularly, yes - it'll be on the schedule (you have looked in your service book?)

But it won't increase fuel use. So long as "sufficient" fuel is getting through, all is good. As it starts to clog, you'll notice misfiring at times of high fuel use - giving it hard throttle, especially cold.

Marlot's suggesting of a stuck-open 'stat is another good one. Heater output is the big clue on that. Ignore all the suggestions of "internal cleaning" your engine - that's snake oil, too.

I still think that 38mpg vs 45mpg is most likely to be simply using the wrong gallon size in your conversion...

oldagetraveller1

"Regarding spark plugs - are NGK or Denso better?" You don't say which engine. I have recently changed my 1.33 litre petrol Yaris (2014, like yours, a Mk 3) spark plugs and fitted Denso, as factory. I can tell you which Denso if it's a 1.33.litre petrol.

If they are the original plugs, probably Denso.

AdrianC

Both are perfectly decent brands, and which you use won't make the slightest difference.

DUTR

sophlouwhit said:

maybe i am over thinking things but i have noticed a fairly drastic drop in MPG. we have a toyota yaris, 2013.

does age effect MPG? does winter effect MPG?

spark plugs are original, car done 80k

new tyres and always kept to good pressure

yearly full service

I would say overal a well maintained car

I have noticed this sudden dip in MPG, where it seems to be drinking a LOT! we used to get 45mpg average now 38mpg average (this is using milage and liters put in vs car computer which i do not trust). Not sure what to think.. does MPG decrease with age? what can we do to help it? to add we add a fuel cleaner which claims to clean injectors every 6 months, once winter and once before MOT (we never used to do this and its a new thing as of last year and hasnt especially helped MPG -2019 average compared to 2018-

Winter certainly has a negative effect on fuel consumption for the reasons and more stated in the replies, I notice a 4mpg difference (on the computer) compared with the warmer seasons, however I don't notice any difference in fuel spend for the week. 

Jackmydad

DUTR said:

sophlouwhit said:

maybe i am over thinking things but i have noticed a fairly drastic drop in MPG. we have a toyota yaris, 2013.

does age effect MPG? does winter effect MPG?

spark plugs are original, car done 80k

new tyres and always kept to good pressure

yearly full service

I would say overal a well maintained car

I have noticed this sudden dip in MPG, where it seems to be drinking a LOT! we used to get 45mpg average now 38mpg average (this is using milage and liters put in vs car computer which i do not trust). Not sure what to think.. does MPG decrease with age? what can we do to help it? to add we add a fuel cleaner which claims to clean injectors every 6 months, once winter and once before MOT (we never used to do this and its a new thing as of last year and hasnt especially helped MPG -2019 average compared to 2018-

Winter certainly has a negative effect on fuel consumption for the reasons and more stated in the replies, I notice a 4mpg difference (on the computer) compared with the warmer seasons, however I don't notice any difference in fuel spend for the week. 

That's because when it's cold, the world shrinks, and so the miles are shorter. . .