GTD economy in hot weather

[jeep15cba]

Hi all,
Now that summer has hit my economy has dropped.
Previously I was getting 5.0L on my drive to work in traffic. Now same route etc and it 6.5+
It's only a few thousand from just being serviced.
Any thoughts? Bad diesel maybe...
Cheers


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[vdubmotorworx]

My jetta is the same...as soon as ambient temp is around and above 30oc fuel eco drops...in winter I can get 4.6L in summer more like low 5's. Its just the air temp and humidity causing it to use more fuel.....

[wai]

Well, hot air is less dense, so less oxygen. Yes, the turbocharger will compress it, but you can see a lower mass and hence lower power output, so you have to increase throttle position which will adversely affect consumption.

There is lower wind resistance because of less dense air, but you can also have different rolling resistance because of temperature. Then there is the AC that will be working more, and you will have the added heat from all the other vehicles in the traffic. There is even the temperature at which you filled the car, and whether you filled up from near empty or after you had used a little. Also, was it from the same service station and bowser and was the temperature the same. This is why in F1, fuel is dispensed in kg rather than litres.

Consumption is a bit like weather. Weather is essentially day to day, whereas climate is over years, decades, centuries,... You need to check it over much longer periods to take out variability that cannot necessarily be measured.

[Transporter]

If you drive normal, the consumption shouldn't change by +1.5L/100km.

How many km the car have done?
I get consistent 10L/100km in my tuned T5 2.5TDI (now done 130k km), mostly driving short distances and that's at any season. Similarly to our 2 Tiguans, the fuel economy is almost unchanged over the year - within 0.25L/100km.

It could be worthwhile to get it checked.

[kaanage]

If you drive normal, the consumption shouldn't change by +1.5L/100km.

Agreed. But perhaps the OP likes to hustle his car along (it being a GTD) so the loss in compressor efficiency in the heat could cause him to use more throttle as wai said, in order to maintain the same performance while most of us let the car perform more leisurely in hotter conditions.

The other consideration is whether the climate control is switching in the air conditioner

[Ryeman]

I thought the MAF sensor took into account temp thus giving the correct fuel quantity for the 'sensed density'.
I've always noted that fuel bought from the bowser actually expands in your tank on a hot day but first thing in the morning chill the level would drop noticeably.
i learnt that the hard way flying in summer.......lot of fuel vented overboard on the tarmac in the late afternoon heat.
F1 used to almost freeze it in the tank so that they could have it expand during the race.

[vdubmotorworx]

Also a very different kind if heat here in Brisbane

[jeep15cba]

GTD is 2011 and just clicked over 36k so rather new still...great 2nd hand buy!!
It was filled up on a very hot day 2 weeks ago, whilst sitting on the hway it was 45deg on the gauge with a horrible dry hot wind. Definitely can count towards something there but this new tank is going to go along the same lines I think.

Just interesting to see the massive differences. It is similar to body weight...check it daily and get a guideline but need to see what happens over a 3 month period to notice major change.

I'm thinking about getting it remapped (for fun not the economy reason) but had a concern of doing this just in case it could be something more sinister.
Thanks for the thoughts!

[Transporter]

Do you always fill up at the same servo? Also the quality of the diesel could fluctuate between them. And pump inaccuracy counts for something as well.

[GTD_XU1]

I have spotted this late, if it's any help to you my GTD is averaging 6.86 L/100km after 113,327km, but I don't drive for economy usually. I have had a few good runs here and there but I nearly always run the climate control pretty cool in Brisbane and real cool when I hit the back blocks plus I run all the gadgets and lights etc all the time.