Petrol/diesel diet challenge – official MSE discussion 17 January 2022 at 10:25AM edited 17 January 2022 at 11:14AM in Motoring 22 replies 5K views

DB1904

Jenni_D said:

It won't be zero effect - that electric power has to come from somewhere, i.e. the battery, so must be replenished. Unless aircon is an example of free energy? (Perpetual motion).  

The alternator runs constantly when driving so maybe you can expand on your theory?

Ectophile

DB1904 said:

Jenni_D said:

It won't be zero effect - that electric power has to come from somewhere, i.e. the battery, so must be replenished. Unless aircon is an example of free energy? (Perpetual motion).  

The alternator runs constantly when driving so maybe you can expand on your theory?

The mechanical load that an alternator puts on the engine is a function of the electrical load you place on the alternator. Conservation of energy has to apply.

So the more electrical things you turn on, the worse the fuel economy.

On old cars, before fancy engine management systems were a thing, you could sometimes hear the engine slow down if you were idling and turned on a big electrical load.

Grumpy_chap

Ectophile said:

On old cars, before fancy engine management systems were a thing, you could sometimes hear the engine slow down if you were idling and turned on a big electrical load.

Or on my 2007 Focus when the air-con kicks in. 
Maybe that qualifies as an old car without any fancy management?
Sadly, the air con is knackered so the negative impact from energy load has no positive in improved comfort.  All the change of engine note does is to remind me to turn the air con off.

motorguy

One thing has changed for us has been the amount of journies we make because of covid.

We both WFH now, so one car has went from £180 a month fuel to maybe £60.  The other would have been £80 a month, now £25 a month.

We also get our groceries delivered now rather than go grocery shopping and to be honest, most stuff we need we just get via the grocery order, ebay or Amazon.  

When we do go out i tend to make it "worth my while" - got a hair cut last saturday morning, picked up prescriptions for my wife on the way past the chemist and also got a top of of groceries we were short of.

None of that is specifically to save money on fuel, but thats the positive side effect.

If i continue to WFH we'll sell our second car - biggest expense there is the £585 road tax (i stupidly didnt check before i bought it).  

jimjames

ElefantEd said:

Step 4. Get an electric car, petrol costs disappear!

What's cheaper? A £500 car that you need to fill with £60 of petrol or a £30,000 EV? That's a lot of petrol before you get to the purchase cost or looking at the environmental impact of a new car vs existing

Herzlos

jimjames said:

ElefantEd said:

Step 4. Get an electric car, petrol costs disappear!

What's cheaper? A £500 car that you need to fill with £60 of petrol or a £30,000 EV? That's a lot of petrol before you get to the purchase cost or looking at the environmental impact of a new car vs existing

There's a huge gulf of options between a £500 ICE car and a £30k EV. ICE cars can cost a lot more, and EVs a lot less; there are EV's on autotrader for under £5000 now. Like this Leaf for £4800:  https://www.autotrader.co.uk/car-details/202201171435865

Ditzy_Mitzy

An oldie but a goodie: ensure your brakes aren't binding.  

MattMattMattUK

The top one is always drive less, I used to use around £120 pcm of fuel with regular commuting, now I use around £40 pcm. Whilst a chunk of that was commuting, I have also got out of the habit of making smallish pointless journeys, I will often walk, sometimes cycle etc.

Not speeding is also a good one, people will burn a lot more fuel on the motorway at 80-90 mph than at 60 mph and on a trip a few junctions up the motorway are unlikely to save themselves any significant amount of time. 

Getting rid of all of the extra weight in the car is also important, I know people that drive around with loads of stuff in their boot, probably 100kg of the stuff, it might be a small percentage, but it adds up over the course of a year's driving. 

Rolyan

Taking your foot off the gas going downhill (when safe to do so considering other road users) while still in gear uses ZERO petrol in modern cars. It adds up over time. 

This is not the same as driving out of gear and coasting, which still uses petrol. 

Mobeer

With so many companies now allowing\encouraging it best advice is to work from home rather than drive to work.