Has your Diesel MPG took a knock?

[Volvon]

I'm getting pretty crap MPG now, around 47MPG, the official book figure is 65MPG extra urban, so I am well off. I haven't had many diesels so I am not sure if they take a bad MPG hit in winter or not?

What are other diesel users getting? Have your MPG's been affected?

[volvorocks]

On a run 36mpg
Round town 28mpg

In winter a little less 34mpg/26mpg

XC60 D5

Regards

[doingitsideways]

I drive a 960 d24-tic...

D24s are dreadful on fuel all year round!!

(Doesn't help when the fuel pump's turned up though!!)

Steve

[gatos]

Mine has dropped about 7mpg. Getting 40.5 at the moment. Cold weather does affect mpg badly

[Volvon]

Thanks Gatos, that has confirmed my suspicions. I have an engine block heater in mine aswell so it's not like I am doing cold starts either, the engine temp is about 50°C before I start the car.

Maybe it is very cold air and very cold diesel not combusting as well as when warm outside.

[LJD]

still wondering if its a good idea to cover the grill to help the radiator warm up quicker etc ?

[Harvey1512]

I've dropped about 5mpg at the moment. The same has happened with my last three cars so I'm guessing it is a winter thing. Logical really, the car has to work harder to get up to temperature and then it has to work to keep the car heated, re-demister etc. Maybe 3-4 minutes idling in the morning to clear ice as well. Roll on March!

[Paddler Ed]

Originally Posted by LJD

still wondering if its a good idea to cover the grill to help the radiator warm up quicker etc ?

I've made some baffles for the BMW as it was only ever at about 1/3 instead of 1/2 at the moment; with the baffle its now up to normal temp. Already saw a .5mpg improvement.

[wimorrison]

It must be the extra load on the engine, and perhaps driving at speeds that are much lower, that cause the additional fuel usage as theory states that a Diesel engine is better at lower temperatures.

The air is denser, therefore you get a better charge of air into the engine for each stroke - on performance engines an inter cooler is fitted to reduce the air temperature entering the engine specifically to achieve the function we are now getting for free - increased air density. A turbo is fitted to get the air back to atmospheric pressure when entering or slighly above, again o increase the density of air entering the cylinder.

The air temperature has little effect on the fuel ignition in our climes once the engine is running, what is wanted is lots of dense air, that enables the fuel to burn more efficiently. The reason a preheat is used when you start the engine is that the cranking pressure is much lower than running pressure and the air needs to be warmer under staring conditions to achieve compression ignition.

The engine will be more inefficient until it warms up, however this will be achieved within a few minutes driving, but not if you are leaving it idling, this takes much longer and gulps fuel. It is possible that the the windchill over the radiator could also be reducing the engine temperature, high pressure systems loose heat quicker and more efficiently than the old low pressure systems.

That's the theory out of the way, practice is often different