Cheapest Petrol & Diesel Discussion Area

AdrianHi

I-LOV-MONEY wrote: »

Thanks for the explanation.

Is there any evidence that one company's additives are any better than another ? Also does premium petrol give a better mpg/performance? I tend to go to the garage which is en route / nearby that sells it maybe 1p cheaper than others. I have loyalty cards for Shell, Tesco, Sainsbury's

Most modern petrol cars can self adapt ignition timing to take best advantage of a petrol with an octane rating up to about 98, some performance cars higher than that. That means more resistant to pre-ignition which does necessarily translate into better fuel consumption or performance, I never measure any benefit on petrol cars with using anything other than what ever was cheapest.
Diesel is a different story, I measure 5% to 7% better fuel consumption with premium diesels like BP Ultimate or Shell V power or using my own additive like Millers which results in a diesel fuel with the maximum useful 55 cetane rating. Cetane rating/number is a measure of how well the diesel fuel burns. Minimum cetane rating for the BS EN 590 standard is 51.
Diesel cetane rating will vary by refinery, time of year (winterised diesel) and simply because the diesel fuel refining process is less exacting than for petrol giving greater variance in quality.
Guaranteed minimum cetane rating by some diesel fuels I know:
Most regular diesel: 51
Shell standard (formerly diesel extra): 53
Total Excellium: 53
BP Ultimate / Shell V-Power : 55
Fuel additives like Millers/Fortes add 4 giving you a guaranteed minimum 55.
Regular shell diesel is arguably best value for money subject to price in your area.
Some additives also perform cleaning and additional lubrication. All diesel fuel has some additive in it to meet Euro diesel fuel quality standards. Raw refined diesel is around cetane 41-46 which will still work OK in most diesel cars but is results in a smokey clattery engine (well more so than usual )
There are independent tests around confirming BP Ultimate Diesels superior cleaning abilities and I certainly measure better fuel consumption with it by the 3rd tank full onwards. Not every one does though and it has nothing to do with how high performance your engine is. With so many factors varying fuel quality and consumption relating to diesel it could be that other factors mask the actual benefit you (or some of us) get.

If I was running a petrol car and had a Shell loyalty card that's probably where I would go in favour of supermarkets whoes post refinery upstream storage and quality control has been brought into question in the period since supermarkets started selling fuel. Lessons have probably been learned by now though

gooeynote

I recently heard about Tesco's promotion of its new premium petrol, momentum 99 and that it saves money overall even though its 5p/litre more than its standard petrol. Its website has link to independent testing/evidence and looks quite convincing.

Anyone had any personal experience with it?

I-LOV-MONEY

No expereince of it. However, you would need to save a lot to make up for the 5p a litre extra. Shell petrol is also supposed to give you more mpg and there's is 2p more than Sainsburys at the moment.

gooeynote

Well the evidence shows an approx 5% price premium over normal petrol but is offset by the potential 15-20% extra miles per tank.

That seems worthy of a try I guess.

I-LOV-MONEY

gooeynote wrote: »

approx 5% price premium over normal petrol but is offset by the potential 15-20% extra miles per tank.

And if it doesn't will they give you your money back? I faithfully record my mpg (and lpg !), together with the price paid for the petrol everytime I fill up.

Ally1205

davetrousers wrote: »

I have heard that when going down hill your car will use no fuel if you leave it in gear and do not coast.

If the engine is still firing, it will be using some fuel (relatively little, perhaps, bet definitely some).

A

John_Pierpoint

It will be slowing you down as the weight of the car will be turning over the engine in top gear - but you are still better off than coasting in most situations - you can always open up the throttle a little bit if you are losing too much speed and you know another uphill slope is coming.
Alternatively if you know a set of red lights is coming you can change down to slow down.

I-LOV-MONEY

What about on an automatic ?

John_Pierpoint

As I remember driving an automatic (and trying not to change gear with my right foot) they stay "in gear" as you slow down?

As a general rule automatics tend to use more fuel as they are constantly churning transmission oil?

I-LOV-MONEY

Automatics do stay in gear. However you can slip it into neutral. Presumably as you are slowing it automatically (!) reduceses the amount of revs and presumably petrol that it uses ? I notice it when moving off, it seems to start high, I reduce my speed, it reduces the revs and I build it up again slowly.