Fuel Consumption and cold weather.

[Munroast]

I have a 10 year old 1.9 litre diesel van during the summer months it achieves about 44mpg this figure drops as the weather gets colder and where the temperatures are continuously below zero it will get as little as 30 mpg. (32% reduction)

My wife has new 2.2litre diesel car. During the summer months this achieves close to 50mpg and even in the coldest of winter weather its economy does not fall below 45mpg. (10% reduction)

Why are some vehicles so adversely effected by temperature. I have considered rolling resistance in case it was an oil / grease issue however I can find no appreciable difference

 

[JohnD]

is it long and short journeys? does the van engine get up to temp?

 

[Munroast]

Both vehicles have a similar mix of long and short journeys, vans engine temperature does appear to be OK, heater is certainly very good.

 

[Burnerman]

You don't say which vehicle this is, but if its one of the indirect mechanical injection types - XUD for example - the cold start device is operated by the thermostat on the block connected to a bowden cable....this pulls a lever on the injection pump a tiny way, increasing the low running injection time as well as increasing the tickover. When the vehicle is fully warm the cable has to be fully slack with 5mm clearance.
Another factor is maybe you are driving in the lower gears.....the gearbox oil could play a very small part as it increases transmission drag - no real deal though.
John

 

[Munroast]

The two vehicles i refer to are a 11 year old naturally aspirated Citroen Berlingo 1.9L diesel van manual ( I don't think I hang on to the gears longer in the winter and doubt if I did it would make a significant difference) and a 2.2L CD Mercedes C Class (i guess Commonrail Diesel with maybe a turbo?) automatic

 

[Burnerman]

I think your Citroen will have the XUD9 motor, with the cold start system I refer to. My own Berlingo (56 plate) has the later but similar DW8 motor - and I wish it would get 44 MPG at any time!
John

 

[Peter.N.]

I have noticed that the consumption of my 406 Hdi increased a little during the very cold weather, it dropped for around 50 to about 46 mpg, part of that is due to the auxilliary heater which fires up at und 10C but I think its mainly due to the added engine and transmission oil drag on short journeys, on longer ones the difference is not nearly as much.

Peter

 

[Donkmeister]

My consumption (1.8 NA petrol) goes from about 38mpg in summer to 34mpg in winter, so again about 10% reduction.

The engine that mine is derived from was originally built to be exceptionally efficient, so has features such as a very small water jacket. This means the engine gets up to temperature very quickly but the pay-off is that overheating problems cause damage to the engine very quickly compared to other designs.

As a van engine is generally built with ruggedness as a driving factor, is it possible that your van is running on cold longer to counter the various adaptations that make it more reliable/rugged? (such as the XUD thing Burner mentioned earlier)

Don't lots of vans have an oil-cooler as standard? Wouldn't that increase warm-up time?

 

[PJF220]

Well cold air is denser than warm air so in cold weather you are getting more air in the engine than when it's warm weather. That's why cars tend to feel like they have more power on a nice cold moring. The ecu will notice the difference via the sensors and should make adjustment to the fuel intake. It may be the difference in the programming on the two ecu's I guess. One may be more sensitive to the changes than the other.