I've had this on both my Fabia Greenline and now my Octavia. If put the heater temperature up, the on board computer reads significantly better fuel economy (5mpg) on a motorway journey. I know that cars are supposed to be more economical driving in cold air however yesterday I had been walking around in the rain with my dogs and they were wet through, cold and miserable so on the journey home I put the heater up (with the aircon on) to warm them up and dry them out -not because it was particularly cold outside.

 

On the Greenline, just turning the heater dial past the 12 o' clock position would cause this phenomenon (with the aircon switched off)

 

So my question is -is this real? or is there some quirk with VW group cars that causes a misreading? 

Forgetting Air Conditioning and that debate.

 

An engine start cold, and the coolant is near the ambient temperature, say 10*oC,  The Oil is near that temperature.

The Thermostat stays closed and the coolant flows around the engine block, and at around 80*oC plus opens and that coolants job is to keep the oil once above 90*oC to that operating Temp.,

 

So Air Cooling the Radiator and Cooling Fans to the Radiator or Oil Coolers, so that uses energy.

 

As a simplification,

if you ever had a Car Boiling, or Overheating in the old days, you drove with the heater on full in that summer day to help keep the Radiator Cooler until you got it sorted.

 

My point is you are taking heat out the System so you are needing less cooling of the radiator.

AC in some cars uses more fuel,

But on some cars the A/C goes on, the revs increase, you potter along, say in an Automatic, the car actually just runs more efficiantely and uses less fuel, the same can happen in a manual, you drive just in a relaxed way, gentler on the throttle and you notice the Instant or Average fuel used is less.

 

maybe putting your heater at open but the fan lower can use less energy as in a alternator charging a battery, but a Fan on in the Cabin, might use the same as an electric fan behind the Radiator.

 

Trial and error and some hypermiling and you soon see what works best.

 

Most of my cars run most economically at 0-12*oC Ambient Temperature, and no A/C on and the car sitting comfortable at 18*C Interior.

Bight Crisp day, no headlights on, Low Friction between tyres and road surface, on cold or cooler roads,

and oxygen is better quality and the engine runs more efficiently.

 

Cars are now designed to be more economic, not just crap ECO TYres and some underbody cladding.

Harvesting Energy and alternators energy so that they can produce battery energy for storage.

Fans and A/C that costs less to run, LED DRL's and Lower Energy using bulbs etc, Intercoolers & Charge Coolers etc.

Cars needing to be more streamline but also keep Engine Temperatures lower but not use energy while doing that.

ie Reducing Frontage & Grills, and air hitting the Radiator only to require more cooling by fans to get the cooling.

 

 

george

Thanks -I understand that having the heater turned up will draw heat away from the engine -but at 60-70mph for 50 miles at 13.5 degrees C outside, I'd expect the radiator not to need too much help -I normally have my climate set between 17-19 degrees (warmer than the outside temp at the moment). Yesterday I turned it up to 24.

From the 15th October when Tesco Momentum is in the Stations i usually notice a better economy, it goes with colder road surfaces, & nice fresh crisp air many days and nights,

& no A/C on unless damp, then the lights would maybe be on etc. so we are back into maybe no noticeable improvement in MPG.

 

Cold fresh air/oxygen i think makes the biggest Fuel Economy gains, there is just the difference between being too cold and engines/coolant /oil taking longer to get up to temp, (once up to temp and driving its easy to feel & notice the improvement.)

and Too warm Ambient where the Oxygen so Air Fuel Mix is not the best and the car is always working to cool the oil.

 

Why its worth looking at fuel use over a year and not day to day, week to week or even for one season.

 

In a gale on Sunday my Fuel consumption dropped 15 MPG on a 110 mile trip i do regularly,

but never have done it in such a headwind,

Funnily in was as windy in both directions, not a tail wind on the return journey to even things out.

 

george