General Poor Fuel Economy

[mclean99]

hey
I've had my punto for abou 6 months now having a fair bit of work done on it,
new gearbox, clutch, cam belt water pump, service, and cam cover gasket as oil decided to pour out the top of engine,
but on friday coming home from work the positive wire going from battery to gearbox had burnt out at both ends, making a 30 min drive home a 6 hour trip, bad times:bang: but after having that fixed i've notice my fuel economy has gone down from50 ish mpg to 28 mpg without any real change in driving, other than going slow due to white stuff being everywhere

 

[fingers99]

That's a negative (earth) cable.

One thing that can affect fuel economy badly is a fubar engine temperature sensor (green coded, next to theremostat on inlet manifold) or (even more likely) a cheap nasty thermostat that's jammed open.

 

[AndyRKett]

This freezing snowy weather can have a dramatic effect on engine temperatures and as a result the fuel economy, without there ever being a fault, the replacing the earth lead will have reset the computer and highlighted the problem

on the 26mile trip to work this morning my car didn't manage to make it up to normal running temp because it was so cold

 

[SweetSugarHigh]

I did a good 50+ mile journey this morning and temp gauge barely got above a third. However, I was still doing a good 55Mpg.

 

[Most Easterly Pandas]

I did a good 50+ mile journey this morning and temp gauge barely got above a third. However, I was still doing a good 55Mpg.

You need a new thermostat then and need to stop believing the trip computer

 

[SweetSugarHigh]

You need a new thermostat then and need to stop believing the trip computer

How constructive...

 

[Most Easterly Pandas]

How constructive...

Ditto.

 

[AndyRKett]

I did a good 50+ mile journey this morning and temp gauge barely got above a third. However, I was still doing a good 55Mpg.

Have to agree with MEP with the engine not warmed to optimum temperature you are some how getting 5mpg more than the cars official figures with it has to be said are pretty spurious at the best of times, and because of the way you have written I took it to mean you did a 50+ mile trip and at one point you looked at the trip computer and for that fraction of a second it said 55mpg on the instantaneous fuel consumption

 

[Ziggy122]

When its cool - my car takes about 1 mile to show heat developing

But in this freezing weather - its taking more like 5miles to show some heat forming inside the engine

Alot of thermostats are proving to be crappy in this weather - they are not able to adjust quick enough as a result you cool down before you realise

Turn the air from fresh to recycle - it means that warm air in the car passes the heater matrix - not a huge blast of icy air

Ziggy

 

[SweetSugarHigh]

Have to agree with MEP with the engine not warmed to optimum temperature you are some how getting 5mpg more than the cars official figures with it has to be said are pretty spurious at the best of times, and because of the way you have written I took it to mean you did a 50+ mile trip and at one point you looked at the trip computer and for that fraction of a second it said 55mpg on the instantaneous fuel consumption

I don't have an on the fly mpg read out on my trip computer, just an average read. I reset the trip before I started my journey and had 55Mpg when I arrived. This seems pretty accurate seen as my actual journey was about 64 miles and I used just a smidge over 6 litres of fuel when I re-filled my tank.

I was just making a point to help the OP that even though the weather is very cold, this shouldn't cause his Mpg to go from around 50 to 28.

 

[Most Easterly Pandas]

I was just making a point to help the OP that even though the weather is very cold, this shouldn't cause his Mpg to go from around 50 to 28.

it will if the car isn't running properly and on top of this is doing a lot of cold starts.

 

[Ziggy122]

well if it helps

my punto - happily does 44mpg on the short runs i do

But since winter has hit - my fuel log is telling my last tank i did - i averaged 21mpg

So the cold is stinging left right and centre im affraid

Ziggy

 

[Brendan W]

The white stuff takes more effort than you think to push aside. Back in the day I did a 10 year track of every fill of a 1.6 TA-40 Celica. Consumption varied sinusoidally over the year from a min of 27 in February to a max of 33mpg in August, every year. Admittedly it was carburetted with manual switchover seasonal intake air heating.