Lower MPG

Jem8472

I am getting lower MPG recently. I have a punto and usually it used to do about 40-45MPG round town, I had a few probs and had a new ECU about a month ago.

But recently just round town driving I am getting about 38MPG. (according to the trip computer)

So is anyone else getting lower MPG as winter has set in or could this be another problem?

SailorSam

Engines run less efficienly when they are cold. Could it be as the weather has got worse and 'cos you're only doing local runs the car is using more fuel.
Check the pressure in the tyres a nd the air filter.

Jem8472

I put some petrol in today and did all the tyre pressures so I am guessing its just the cold weather

rev_henry

Honest John wrote about this a few years ago, the difference in MPG in summer and winter can be quite considerable. It would appear to be quite a coincidence that you had a new ECU though!

harveybobbles

Also, you'll be driving evertywhere with the heaters on full, the heated rear screen, lights etc all on... Using more battery, which uses more fuel...

thescouselander

Could well be the cold weather. Cold air is more dense so the ECU will pump in more fuel since more air is going into the engine. On the plus side you should have a bit more power.

vikingaero

Definitely the cold weather. The engine will be running rich for far longer as it warms up and the load of all the electrical items. Some car manufacturers tell you to check tyre pressures when the tyres are cold. For some manufacturers that means at 13-16 degrees C. For others they mean at 0 degrees C. Whereas a few weeks ago we had temperatures of 12-15C, and now we are around freezxing, I've found that my tyre pressures have been out by 3-4 psi.

Also with the amount of rain we've had, driving in rain uses a lot more fuel because of the drag of water.

AdrianHi

I always see about a 10% increase in fuel use in colder temperatures. I assume it is down to running heaters (the heat energy can only come from the fuel), taking longer for the car to warm up and the colder air sucking more heat out of the radiator and engine bay.

Ebe_Scrooge

AdrianHi wrote: »

I always see about a 10% increase in fuel use in colder temperatures. I assume it is down to running heaters (the heat energy can only come from the fuel), taking longer for the car to warm up and the colder air sucking more heat out of the radiator and engine bay.

It's a lot to do with electrics, as Harvey said earlier. Anything that puts a drain on the electrical system will increase fuel consumption ( ultimately the electricity comes from burning fuel ) - e.g. heater fans ( a small amount ), headlights and rear-window demisters, quite a considerable amount. Plus the battery has to work a little bit harder each time you start it ( compared to summer ), so takes that bit more to recharge when the engine's running. It all adds up.

But you're also right in that an engine won't run as efficiently when it's cold as when it's at correct operating temperature, so if it takes longer to warm up then its spending longer running inefficiently.