Could anyone enlighten me as to why I appear to have suffered an apparent drop of about 10 mpg with my CR170 diesel after 7000 miles.

I was always led to believe that mpg figures steadily improved over time. When I first had the Yeti, I was achieving a very satisfactory average of around 46 mpg on the run to work. Now, that average is looking more like 37 mpg! I don't understand it. The engine seems to be running OK and has loosened up quite a bit. The only difference I am noticing is that I tend to perhaps run at lower gears in general because of the loosening up and rpm against speed seems lower than what it was when new.

Perplexed and concerned! At this rate, I'll have got better consumption from the Audi TT my Yeti replaced.

Could anyone enlighten me as to why I appear to have suffered an apparent drop of about 10 mpg with my CR170 diesel after 7000 miles.

I was always led to believe that mpg figures steadily improved over time. When I first had the Yeti, I was achieving a very satisfactory average of around 46 mpg on the run to work. Now, that average is looking more like 37 mpg! I don't understand it. The engine seems to be running OK and has loosened up quite a bit. The only difference I am noticing is that I tend to perhaps run at lower gears in general because of the loosening up and rpm against speed seems lower than what it was when new.

Perplexed and concerned! At this rate, I'll have got better consumption from the Audi TT my Yeti replaced.

Winter diesel!? Some people say there is no such thing but the formulation has to be changed for the colder winter months to stop it waxing... my daily commute in a TDCI drops from 51mpg to 45mpg as soon as the local station changes over and then picks back up when they return to the summer stuff in the warmer months.

Also, the diesels arent great at warming up in the cold months so Id guess if the engine is taking longer to come up to temperature then the overall fuel usage will suffer.

One reason why I didnt buy the CR170 - optimally achieved figures, for me at least, arent realistic figures!

Edited 19 November, 201015 yr by FocusZtec

It is the weather.. The engine is cooler for longer, meaning the car is in the warm-up cycle for longer, thicker diesel meaning the injectors stay open for longer, different diesel mixture to stop waxing etc.

We get lots of customers complaining about economy issues over the winter that magically disappear as soon as it warms up again..

Kev

Agree with previous comments, finding the Yeti is taking far longer to get up to temperature and hence knocking average MPG.

Slightly off topic, but an associated point, have you tried the new Shell Diesel?

My local garage swapped over some weeks ago and I noticed an immediate improvement in mpg. I cover about 20,000 miles a year and so have been through a few tankfuls now and had to fill up from practically empty last week with BP and noticed the mpg dropped back. I find it hard to believe myself as all the oil companies say theirs is best, but this does seem to have something behind it (this is Shells new normal diesel, not the more expensive stuff).

Interested to hear if anyone else has noticed this.

Thanks for the explanation guys.

I must admit I've always found Shell fuels to be better as well. I did tend to use the v-power diesel though, when my previous employer was paying the bills.

Now I'm self employed and have to pay my own.....I will see.

Mike

Winter Diesel is genuine and is not hidden by oil companies. It is a necessity as otherwise diesel would freeze at even English cold weather temperatures, think driving over the Yorkshire moors at -2C plus a wind chill. The fuel itself is barely changed, they just put in an additive that brings the freezing point down. That in itself should not really impact on your economy, it is more a case, as others have mentioned, that your engine has to work harder at the beginning to get warm. I am surprised though that the difference is so large, I have normally experienced a 2-3 mpg difference between summer and winter.

I suspect that your increase in consumption is a combination of all of the above. You do admit to giving it a bit more Welly, with more revs.You didn't say how long your commute to work was? I drove very high mileages in my diesel commuting days and my consumption showed no discernable difference between summer/winter. Just a final thought ,have you checked your tyre pressures recently?

Very Interesting

I have just checked the consumption on my 4 year old Passat 170 and there is indeed a sudden drop in fuel economy coinciding with winter months. If this was due to winter conditions this change would not be a sudden jump but would gradually change with the seasons, so the idea of winter diesel not being as good makes more sense.

I haven't analysed it in detail but I reckon the difference is about 6mpg (av37 in winter av43 in summer). I keep records of all fuel purchased for business purposes and I had not noticed this effect.

Other factors which could make a difference

Heated Screens, Mirrors, Longer warm up as mentioned

But! Air con not running so should be a net winter gain.

Oil companies start adding the additive into winter diesel from around September onwards, at least that is what they used to do and I see no reason why they would have changed. This is so that by the time you reach the middle to back end of October all storage depots will have their tanks full of Winter diesel, depots do not let their tanks go empty and then fill them, it is a constant topping up process so it takes a while for the mix to fill to be 100% in the system. If the fuel was the main issue then you would have seen a drop off from around mid to late September as the reality is the fuel is 100% winter safe earlier rather than later, oil companies are very cautious on this one.

Soooooo if your fuel consumption started to drop off from November onwards then it is not the fuel as you will have been using winter diesel from the beginning of October at the absolute latest and probably before then. If your fuel consumption started to drop from September/early October then the fuel may be affecting your car although I still think that it is other factors.

The anti-waxing agent, which is actually what the anti-freeze is, is as Edmund suggests added from September onwards, so by now all the diesel sold will contain it, at the full percentage. It is a very small percentage by volume, I think less than 2%, and will make no difference to the fuel consumption. The reason that goes down is because the engine takes longer to warm up.

Hi

If the explanation of increased fuel consumption resulting from longer warm up times is correct then its a shame we don't have an automatic equivalent of the radiator blind I had on my first car to reduce air flow through the engine compartment. I presume having a thermostatic cooling fan goes some way towards the same goal.

Also, back then the heater was feeble and not worth turning on until the engine was warm. To prevent the windscreen from misting up one drove with the windows open (well wrapped up against the cold).

Is the fuel consumption higher because we have effective heaters and use them instead of wearing warmer clothing - thus keeping the engine cooler for longer?

If so then to be ECO wrap up warm and don't use the heater until the engine is up to temperature - about 6 miles with my 140PS diesel.

Which is more efficient - a heated windscreen or using the heater to warm the screen? I hope its the former having ordered the option. The electrical load will increase fuel consumption but hopefully not as much as using the heater blower.

Fred

Could anyone enlighten me as to why I appear to have suffered an apparent drop of about 10 mpg with my CR170 diesel after 7000 miles.

Dave, how long is your commute?

Try checking the oil temp on the MFD readout, it takes around 15 mins to reach the optimum 95-100C in this cold weather.

is you car left outside overnight?

As others have said it must be down to the cold weather.

Are you keeping your butt toasy warm with the seat heaters, :yes:

The engine on my 140CR isn't even up to temperature when I park up at work after my 5 mile, mostly downhill, daily commute. Though it does manage to hit the 90 degree mark on the uphill return leg. I'm guilty of cranking the heating up and having the electric seat heaters on full from the get go so I only have myself to blame for the 36mpg I've managed over the cars first 700 miles I suppose

Mind that's about a 25% improvement on the previous 1.8 petrol Octavia so I'm still quids in