Diesel engines and warm weather !

[Krise]

Afternoon all, hoping the PH massive can shed some light,

I do big miles approx 1500 - 2000 a week, currently running a 58 plate TDCI 2.0 focus, up until the weather getting warmer I have been managing an average of 55mpg, of late I'm struggling to keep it above 46.

Does the hot weather have anything to do with this ?

[Doofus]

Having the aircon on?
Windows/sunroof open?
Surfboard on the roof?
Boot full of buckets and spades?

Dunno...

[V88Dicky]

46mpg? You can get decent petrol cars that do more than that, thats not to mention the fact that its 3ppl cheaper for the fuel.

[bob1179]

Air is less dense when it's hotter so you don't quite quite as efficient 'burn' in the engine. However I wouldn't have thought that the warm weather would effect fuel economy to any great extent.

[Krise]

To add, I very rarely use the aircon, the car is empty aside from me and maybe a suitcase, not doing anything that I haven't been doing before !

[Big E 118]

Doofus said:

Having the aircon on?
Windows/sunroof open?
Surfboard on the roof?
Boot full of buckets and spades?

Dunno...

^^^^aircon

[Balmoral Green]

Hot weather, power down, fuel consumption up, especially on a turbo car. It's the density of the air in the charge, that's what intercoolers are for, to bring the charge temperature down.

My turbo diesel Fabia doesn't like the hot weather, slows it down a bit, and the Bentley hates it, power loss is very noticable.

[Krise]

Would the air con really make that much difference, nearly 10 mpg, like I said I use it very little

[Jayho]

If you open up your windows you also compromise the airflow over the car...

There's probably a power decrease due to the density of hot air compared to the warm air which has a knock on effect on how you drive... You'll be putting your foot down more (Probably) to compensate without knowing.

[ukzz4iroc]

I used to notice a big difference with my A4 S Line TDi in the warmer weather. Turbos like lots of nice cold air.

[liner33]

I get my best mpg this time of year ,i often have mid to high 50's , i'd check the air filter

[OnTheOverrun]

Google VE or Volumetric Efficiency.

HTH

[J4CKO]

I think its because diesel drivers feel the need to hoof it past cyclists and leave us with a noisy whilst and clatter then a big cloud of stinking sooty hot air.

[interloper]

Thats a big loss of mpg. Even running around with the windows and sunroof wide open on my diesely shed, only knocks 2-3 mpg off. Have you checked the obvious like your tyre pressures? Or wether you have a brake binding?

[Ry_B]

I love cold air, warm air makes your car slower and do st mpg. People say in the winter their cars are worse on petrol, I find mine to be better in winter. Probably because I'm not going as fast and the air is colder.

[kiethton]

I have always found the MPG better in the summer in my astra diesel and do about 2-2.5k a month. Its only a couple of MPG worse in winter but i put it down to rain and wetter roads.

[Triumph Man]

I find my car is better in cold weather, runs far better, and it's not a battle to start it from hot after standing for 10-15 minutes, as in hot weather the heat soak is worse with inevtiable fuel vapourisation. Also I can choose how hot or cold I want to be. In the summer this is dictated by the car's vinyl seats....

[DaveL86]

I have a Bora TDi PD130...

Somethings clearly wrong with my car, I find my car feels much quicker and punchier in the warm weather also get much more mpg, whereas in cold weather its the opposite.

[Ry_B]

kiethton said:

I have always found the MPG better in the summer in my astra diesel and do about 2-2.5k a month. Its only a couple of MPG worse in winter but i put it down to rain and wetter roads.

That's the reason why I think mine is better in winter - wet roads = less revs = less speed

[Munter]

I wonder if those getting better economy in the summer do shorter journeys. And therefore burn more in winter getting the engine up to temp than they do in the summer. While those doing 1000s of miles a week are finding the lower hot MPG negates the benefit of a "warm start".