Headlights on means less mpg?

On my V70 the lights are usually on all the time regardless on the switch position, but I turned off the DRL setting a while back to see if it made any difference to the fuel economy. I use just over a tank of fuel a month and with the lights off most of the time, on the last tank full it averaged 31.6mpg. Now I've turned the DRL setting back to lights on all the time and done a couple of hundred miles of normal driving with the heated seat on and occasional air con use too and it's averaging at 34.2mpg.

I might have done a bit less town driving than before which helps but it's warmer outside too so the engine is up to temperature quicker

I realise that having the lights on all the time does use energy which comes from the fuel but it's such a small amount compared with other driving variables that it's not worth bothering about.

It will be interesting to see if you notice any difference Dave.
 
I got 25 mpg on my way to see Ian Wilson yesterday to do the springs on PAE. Was pleased with that. PAE is going to be off the road for a few weeks while i get the welding sorted for the MOT but after that i'll definitely keep an eye on it to see.

It does occur to me that there must be a market for retrofitted regenerative braking systems for classics. Makes me wonder if something could be done that would fit lots of classics rather than just the P6. It would improve MPG and power too no doubt...

Rich.
 
25mpg's not bad is it? Probably the 'easiest' things to retro fit on to a classic that would save fuel are a disengaging alternator and electric power steering, but both would still be mammoth projects for a DIYer.
 
25mpg is great when you consider it's not been near a garage and i've done everything by ear on the carbs following helpful instructions from Chris york mostly. The engine i purchased from chris w was definitely in good nick too which definitely helps.

When i'm a bit happier with the whole car I'll see about removing the mechanical fan and see how it copes with just the electric one which should help a little more...
 
Other one is the electric water pump - they're quite expensive but the amount of mpg extra from this would be significant. The fan belt would only need to drive the alternator then!
 
I've been thinking of using an electric steering rack in my coupe project, although fuel consumption has nothing to do with it, more to do with a neater and potentially easier installation.

Also I've noticed that HID kits use less power than halogen bulbs, so if you're thinking of converting to halogen, you may want to convert to HID instead.
 
Hi all,
for anybody covering alot of motorway mile I reakon you actually save fuel by driving with the lights on as slower moving drivers in the fast lane see you sooner and tend to move over quicker, saving waste full braking!
Regards,
Dave
 
On the subject of electric water pumps,...if the belt then is just used to drive the alternator, what turns the fan and where does it go? Does using an electric water pump then mean that you must also fit an electric thermo fan?

Ron.
 
Hi Ron,

I guess so - I must admit to liking the efficiency of that idea - especially if coupled with a heating element to warm the engine up before starting! I'm sure it must be possible to find another belt to fit easily enough...

Rich
 
Electric water pump is a step too far for me, I like the simplicity and reliability of the mechanical pump, quite keen on electric fans though.

Another interesting question regarding electric water pumps, do you still use a thermostat, or just turn the pump off (or vary the speed of the pump to control flow of coolant) ?
 
webmaster wrote,...
Another interesting question regarding electric water pumps, do you still use a thermostat, or just turn the pump off (or vary the speed of the pump to control flow of coolant) ?
Click to expand...

Hello Richard,

The thermostat plays a dual role, setting both the minimum operating temperature for your engine, and reducing the speed of coolant flow so that it has time to remove engine heat before being passed through the radiator for cooling. Running without a thermostat therefore is most certainly not advised.

The size of the OEM pulleys sets the speed with which the water pump circulates the coolant, and this speed is critical in ensuring that the engine does not run too hot nor too cold. As engine speed increases, so heat increases and water pump speed increases to compensate.

I do not know what volume of coolant the OEM water pump moves for ever 100 revs per minute, but I would expect that an electric pump would need to move an equivilent volume for the same engine speed. How it would change the flow rate to adjust for engine speed variations I do not know.

A fan not running via a viscous coupling would have the largest impact on maximum engine power and thus on fuel consumption. I feel the load that the water pump imposes especially at less than maximum rpm would be quite small by comparison.

In addition, the more ancillaries that are transferred from mechanical to electrical operation will require the alternator to return more current to the battery, so the OEM Lucas 11AC or 18ACR will likely prove to be too small in terms of their current output. Uprating the alternator to compensate or just making do with the additional electrical loads will increase the load imposed on the engine, so the net effect on fuel consumption may be zero or......

Ron.
 
Sorry Ron, but I beg to differ. The discussion over power saving is more or less identical to the engine driven fan vs viscous/electric, except that the medium is water rather than air. Briefly, in order to get an adequate circulation at idle rpm, the water pump is massively overspecced for high rpm, thus wasting oodles of power. In the UK at least an electric water pump is a standard modification for circuit racing. Of course you do have to take the innards out of the original engine pump.

Actually, if you arrange the temperature sensing carefully, I see no reason why varying the electric pump speed shouldn't be a completely adequate substitute for a thermostat. Like you I wouldn't stop it altogether, but two speed is quite feasible.

If you are going to the trouble of fitting an electric water pump then for sure you will already have ditched the engine driven rad fan in favour of electric!

Chris
 
Hello Chris,

Hmmm... :? I do enjoy a good discussion,,,, :D

The OEM water pump though would not result in caviation at high engine speeds else that would leed to all sorts of problems.

Hmmmm,....don't know about removing the thermostat....I am not liking that idea.

You have given me homework Chris,...I shall return.. 8)

Ron.
 
From what I'd seen the MPG saving is supposedly large ( I've only looked at them online - never had any practical experience!) An extra 6-7mpg is a big difference!

Rich.
 
combine that with a water heater for quick getting to temperature then it could be an interesting experiment. At the moment the car has more important things that need doing but that's something i have in the back of my mind....
 
On second thoughts, you would need the thermstat in a road car as it prevents flow through the rad whilst allowing flow through the heater matrix, if you removed it you would more than likely suffer a much slower warm up rate, especially in the heater.
 
Not if you also put a primer pump in the heater circuit - see the Davies Craig link that Ron put up - you could link it the blower fan!

Chris
 
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.
 
chrisyork said:
Not if you also put a primer pump in the heater circuit - see the Davies Craig link that Ron put up - you could link it the blower fan!

Chris
Click to expand...

Sounds like a complex solution to a simple problem, a bit like using an iPad to read a book.
 
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