172 Cup - weird MPG drop

[montana]

Had my cup about 3 months now, i reset the onboard computer each time i fill up and at first i was averaging 38mpg, recently however this has dropped to 35mpg on my commute (same driving) - the car has had the oil & filter changed along with plugs (no modifications) and the only difference i can pinpoint is i have switched to Tesco SUL (99)

Could Tesco SUL explain this 3mpg drop alone ? Does weather play a part?

Before anyone thinks i am whining over 3 mpg - i am not,previously I have been used to 25mpg (at best) from my previous import WRX so the clio is decent on fuel.... I am just curious

 

[Damo_Sport]

i never use tesco sup.. saying that i put in tesco ghetto the other day as i was caught short and its lasting forever lol

 

[freeman(clio)]

cold start in this weather will be prolonged, therefore resulting in bad mpg, plus if your leaving your car to warm up/defrost on a morning

 

[Damo_Sport]

like freeman said, in the winter its alot worse...

 

[EllD90]

Engine runs leaner in the cold, therefore uses more fuel? Maybe? Who knows...I'm probs talking shoite!

 

[ilovewilly]

It would only take a different journey, or a trip to the shops though town once in that tank to take it down.

I understand you said same driving, but maybe you had a heavier foot, bit of traffic one of those days.

 

[Arney]

cold = choke on for longer. leaving car to warm up etc... plus winter fuel is slightly diff from summer fuel and has been noted to reduce fuel economy. my 182 sits at 33mpg all day everyday unless on a long run the see about 37.. (leaner = less fuel richer = more fuel).

 

[Kam.]

usually engines run richer when cold. My mpg is certainly down about 4 mpg. I was getting 42mpg on regular gas but with Vpower im only scraping 40.
I dont let my engine idle when I wipe the snow off either but its taking a lot longer to warm up.

 

[sideways danny]

Engine runs leaner in the cold, therefore uses more fuel? Maybe? Who knows...I'm probs talking shoite!

cold air is denser. Air temperature compensations will add more fuel to account for this. Also if the coolant doesn't get up to temperature fully (due to old or inoperative thermostat) then that will also be a source of extra fuel being added.

Worth checking the lambda sensor is operation correctly too

 

[EllD90]

So the engine effectively overfuels in the cold conditions, to keep it safe?

 

[Fletcher]

I would also put it down to the cold weather.

 

[sideways danny]

So the engine effectively overfuels in the cold conditions, to keep it safe?

no, it's not overfueling. It actually needs more fuel to keep correct AFRs due to cold air having a greater density. You're only talkinng about approx 7% more fuel if the intake air temperature is 0

 

[montana]

cheers for the input fellas