Winter MPG

Is there any reason why my fuel economoy has got worse over the winter months - same driving conditions, mostly motorway 60mph average. Back in the summer was getting 400miles to the tank - now struggling to get to 350. Recently serviced - filters oil etc...

Searching posts it seems I'm not alone - but whats the theory behind this - I thought cooler air would result in better performance (hence intercoolers) and therefore better mpg?

Could the preheater being on more often be a cause - thought that'd be ofset by getting the engine warmed up quicker.

Any thoughts?

What age, what engine, have you got a fuel burning heater?

Davec said:

What age, what engine, have you got a fuel burning heater?

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TD4 04 auto yes has FBH - like I say driving conditions mostly the same 40mile each way to work motorway mostly - only difference being colder air temp.

Would the FBH make such a difference?

I think it has to be below about 5°
Mine's a Td4 Auto (no FBH) and I've kept a record of every drop of fuel put in, and I can't say I've noticed much difference during the last 3 1/2 years.
Mainly across the welsh mountains, half on B roads.

mines also a td4 auto, and I can't say I've noticed any difference, and my records are pretty accurate(for tax reasons).
That said, in the winter there is extra load on the engine, lights, heated rear windscreen etc, so it all works a little harder. As a matter of habit, I always have my headlights on when I'm driving day or night, along with the aircon, so maybe that explains why I haven't noticed the difference.

Also, the fuel will be more dense in the cold, so for a given volume, more fuel by weight. Does that make a difference ? F*cked if I know.

just been having a conversation with a work mate , he seems to think when he buys his fuel (diesel ) from tesco, his citroen loses over 70 miles per tank, he thinks its very low grade fuel,?

also this guy use to work at a research centre, and was telling me to add a 1/2 gallon of petrol to a tank of diesel ,says it raises cetane value and inproves efficiency, ,,,,, has anyone come across this before,,,,, im not sure i want to risk thining the lubracating properties and fook the pumps

Not sure about the diesels, I dont work on them.

I wouldnt add the petrol, but the additives that clean the inhjectors, do exactly what they say on the tin.

More fuel consumption in the petrols too, higher/longer warm up times, so higher idle until warm

john t said:

just been having a conversation with a work mate , he seems to think when he buys his fuel (diesel ) from tesco, his citroen loses over 70 miles per tank, he thinks its very low grade fuel,?

also this guy use to work at a research centre, and was telling me to add a 1/2 gallon of petrol to a tank of diesel ,says it raises cetane value and inproves efficiency, ,,,,, has anyone come across this before,,,,, im not sure i want to risk thining the lubracating properties and fook the pumps

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Petrol to the diesel?? Sounds a bit risky, but at nearly 10p a litre cheaper I'm thinking maybe the petrol versions work out cheaper on fuel? (although not in repair bills perhaps?)

Northern Irelander said:

Not sure about the diesels, I dont work on them.

I wouldnt add the petrol, but the additives that clean the inhjectors, do exactly what they say on the tin.

More fuel consumption in the petrols too, higher/longer warm up times, so higher idle until warm

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I find that Millers diesel additive makes a noticeable difference.