Headlights on means less mpg?

keynsham1 said:
Going back to the lights issue, the only source of energy a car has is petrol. All other forms come from burning it (potential energy, kinetic energy, etc) So it follows that whatever you do, whether it is putting lights on (electrical power is required) or leaving the window open (more aerodynamic drag), you will use more petrol.
Click to expand...

True, but there are more efficient ways to get the energy you need, and there are a lot of losses involved in some of the conversions. All the heat we have to dissipate in the rad, exhaust and brakes is all wasted energy, plus we use even more energy to get rid of the heat by running the fan and water pump etc.

Regenerative braking helps to prevent loads on the alternator by charging the battery rather than generating heat in the brake disks. How about installing a steam turbine to generate electricity from the heat of the exhaust manifold ? :D
 
nice :-D My first car inherited from my mum was an MG metro... Was fun at 17 years old! till my dad trashed the engine...

Was nothing to do with an iPad though so that's ok isnt it? Please dont look down on me for this minor misdemeanor ;-) (hope i spelt that right...)
 
Dave3066 said:
Gents

I rediscovered this thread whilst searching for something else to do with the current thread on batteries elsewhere on the forum. I thought it might be interesting to resurrect it, particularly as we move into the dark/cold/wet autumn/winter days, to see if people were experiencing this effect of increased mpg with increased usage of wipers/demisters/lights etc.

It might be a bit early to tell but for those of us driving our cars through the winter (or is it just me who's mad :twisted: ) it would be interesting to see physical evidence of this. I keep a log of all my fuel and mileage for business use so I'll have a good picture of my own fuel consumption.

......and before people start mentioning the other variables that can affect fuel consumption.....the proof of the pudding will be if our fuel consumption improves again as we move into spring/summer next year.

Dave
Click to expand...

Now that we're moving into Spring and the temp has warmed up a bit (well for you guys down south anyway :) ), I hear it got up to 22 degrees in Suffolk yesterday, I thought I'd bring this thread back to the fore and post some results of my fuel consumption since we last discussed this.

I record all my fuel and mileage for business reasons anyway so it was simply a matter of setting up the spreadsheet to calculate fuel consumption. The results since July last year (in mpg) are:

Jul 25.8; Aug 25.1; Sep 25.6; Oct 25.2; Nov 23.7; Dec 22.3; Jan 22.5; Feb 23.2; Mar 25.2

These results would seem to indicate a definite increase in fuel consumption as the days get shorter and colder, presumably from the increase in use of lights and heater blower etc.

Roll on the Summer then :D

Dave
 
That's really interesting!

Also means that the more work we put into more efficient lighting etc, the better fuel consumption we'll achieve. Other thing of course is the engine warms up more quickly in summer?

Rich.
 
Interesting reading there Dave.

Certainly with a fuel injection car the quick it warms up the better the fuel consumption - presumably that would carry over for a carb engine too.

The ultimate test of that would be if you carried on driving with your lights on now the weathers warmer.
 
testrider said:
The ultimate test of that would be if you carried on driving with your lights on now the weathers warmer.
Click to expand...

....and the blower motor too. The wipers will be on anyway......well it is Scotland remember :D

That would be an interesting continuation of the trial. Problem is that I'd end up forgetting the lights were on and draining the battery when I stopped :roll:

It's warming up nicely for the weekend up here though and it is good to be able to turn the key and have the engine start from cold without any choke too.

Dave
 
The answer to this seems quite simple. An engine only has one source of energy and that is petrol. The total if the total energy output from all loads on the engine increase, then you must use more fuel. You cannot get more energy out unless you put more in (you cannot create energy, it is a constant). Of course, the battery is an energy storage device, so this complicated the process a little.ie, if your alternator was removed, your lights will still work until the battery is flat. So you have two sources of energy for the lights: the engine, and the battery. The same still applies though. If you use the lights, the energy to run them must ultimately come from petrol.

The reason that engine revs drop so much when headlights and demisters are turned on is because the engine is producing such a small output at tickover that any drain will affect it. Think about the fact that you can turn your engine by hand if you try, and so the power produced by the engine just to turn the engine over must be tiny!
 
You must log in or register to reply here.
Back
Top