Tesco super unleaded test

[Will]

I have been getting 260miles from a full tank with unleaded, full tank of tesco's super unleaded i got 300miles.

It's only about 3MPG extra, but... Every little helps

Hi Don,

As the others have said, this is most likely a 'placebo' effect.

The reason I say this is your car (the W124) runs a pretty old fuel injection system - the Bosch K-jet setup. It doesn't have knock sensors on the engine or anything so it can't really make use of the super-unleaded unless you adjust the timing by altering the EZL trimmer.

It's a mechanical system and will still inject the same quantity of fuel whether it's standard or super unleaded.

I guess the warm weather is helping things quite a bit

Will

 

[Laurie]

Have I read somewher that petrol expands with heat ?

So it is best bought in the cold and will, perhaps, increase slightly on a warm day ??

Conversly I believe a turbo diesel runs at it's best on a very cold day

 

[Donbronski]

Hi Don,

As the others have said, this is most likely a 'placebo' effect.

The reason I say this is your car (the W124) runs a pretty old fuel injection system - the Bosch K-jet setup. It doesn't have knock sensors on the engine or anything so it can't really make use of the super-unleaded unless you adjust the timing by altering the EZL trimmer.

It's a mechanical system and will still inject the same quantity of fuel whether it's standard or super unleaded.

I guess the warm weather is helping things quite a bit

Will

I have the a carburettor but same goes i suppose. I had thought of advancing my timing to running on better fuel, would that be a good idea?

 

[Donbronski]

Have I read somewher that petrol expands with heat ?

So it is best bought in the cold and will, perhaps, increase slightly on a warm day ??

Conversly I believe a turbo diesel runs at it's best on a very cold day

Erm... the particles in air/oxygen are bigger when cold & smaller in hot air, not sure of the maths or physics but they say cold air intakes add BHP & thee other MPG

 

[wemorgan]

The ideal gas equation is:

Pressure * Volume = no. of moles * Gas constant * Temperature

So as Temperature rises so does Volume.

Whilst the air may be more dense on a cold day I suspect also that the engine will take more time and energy to get to full operating temperature.

 

[saorbust]

My what an interesting topic. I have noted that since putting in Branded Fuel (either BP or Shell) my range on a tank has gone up, from 280 to 350 ish. That's on an 80 litre tank in a 5.5 V8 engine, and the change is from Tesco 99 Ron.

It works for me - but I freely acknowledge it may be the placebo effect. But given the price difference which is marginal I'm happy to continue using BP or Shell.

 

[alanf]

I wonder if any of you received an e mail similar to one i got last year. In a nutshell it originated from someone in the petchem industry and he was saying buy your fuel early in a morning if possible as the tanks will have settled due to lack of use so any sediment will be at the bottom (if the delivery tanker is at the garage drive on),also the fuel is cooler so you get more as it contracts.If i have kept it i will post the full e mail.


alanf

 

[Beetnik]

I've just had a look on Shell's website. There's lot's of 'it's designed to...' and 'it may...' but no 'it does...'.

I can't beleive that, having spent so much money refining (oops!) their product they haven't done an array of properly conducted scientific tests on it. If the results proved the hinted claims they make you can bet your bottom dollar they'd have published the results but they haven't as far as I can see. So ask yourself the question - if they've done the tests and not published the results then why not?

Psychology is a powerful marketing tool.

I've got 29.6 mpg over the last 10k miles; about 25 around town and 35 on runs. Last week I did a run to Wales and was astounded - for the first time ever the display read over 40 mpg for quite a while and I've never seen it above 38 before. Overall around 10% better than I've seen before. And the fuel used - exactly the same as for the last 10k miles.

 

[wemorgan]

In the above equation, temperature is measured in Kelvin

Celsius + 273 = Kelvin

So if in the morning it is 10C=283K, then in the afternoon it is 20C=293K, then there has been a 3.5% rise in temperature, so for constant pressure, there will have been a 3.5% rise in volume. So 50 litre of fuel would have expanded to 51.5 litres.

But would the energy density not have reduced by a proportional amount, so the car would need to pump more fuel?

Anyway, if you fill your car up to the brim on a cold morning then park it in the sun doesn't the expanded fuel just overflow onto the street!

ps. hope my fluid equations service me correct.

 

[Beetnik]

All well and good but you can't look at the volume of fuel delivered in isolation. It's measured by a device which is also subject to expansion/contraction as a result of temperature.

Let's imagine a gallon of fuel inside a metal fuel container with a mark at the one gallon point. Temperature rises causing the fuel to expand by 3% and the container by only 1% (they have different coefficients of expansion). The 'gallon' of fuel will now go above the 'one gallon' mark in the tank so if you decant one gallon of the fuel into your car you'll actually get less as some will remain in the container.

 

[wemorgan]

Good point, I hadn't thought of the expanding vessel too.

Though the the amount of energy within the fuel surely remains unchanged regardless of its volume?

 

[Beetnik]

Yes - if it's the same mass of fuel but at a different volume but in this case the mass you're fueling the car with has changed - you've left some of the fuel, and therefore some of the energy, in the container.

 

[BTB 500]

I've just had a look on Shell's website. There's lot's of 'it's designed to...' and 'it may...' but no 'it does...'.

I can't beleive that, having spent so much money refining (oops!) their product they haven't done an array of properly conducted scientific tests on it. If the results proved the hinted claims they make you can bet your bottom dollar they'd have published the results but they haven't as far as I can see. So ask yourself the question - if they've done the tests and not published the results then why not?

Psychology is a powerful marketing tool.

There have been independent tests showing bhp and torque increases with 'premium' fuels (compared to standard fuel, checked on a dyno). But this benefit isn't universal - it depends to some extent on the specific car and engine. So it's not possible to make any simple statement like 'gives x% more power'.

I know that Shell Optimax (and then V-Power) made a difference in my V6 4Motion Sharan because:

a) when towing the caravan, 6th gear was basically unusable on standard fuel but OK on the premium stuff (more torque)

b) repeating the same cross-Europe run using different fuels I consistently got more range on premium fuel (making the "one fuel stop" strategy comfortable rather than nail-biting!).

 

[JonnyCJ]

Yes - if it's the same mass of fuel but at a different volume but in this case the mass you're fueling the car with has changed - you've left some of the fuel, and therefore some of the energy, in the container.

Surely the temperature underground will remain fairly constant ? apparently ground temp is 12 degrees 3 feet down irrespective of the ambient temp...

 

[Donbronski]

OK, so when adjusting my ignition before i started using high grade fuel it would knock if i got too close to the more advanced side of the scale, what i mean is... my timing @ idle is ment to be between 10*-16* when near 16* it would knock up hills & underload etc...

Now having run throw some hardcore tesco fuel.


Would i be able to advance my timing futher? And is this a good thing?


I dont wont to go fast... im quite happy cruising at the speed limits,

 

[Phil Thomas]

I think the warmer weather and longer days account for it. I've been getting an extra 3 MPG and I haven't switched fuels.

Not sure about this, but you could possibly change fuel without knowing. It depends on your supplier's source? I suspect Tesco go looking for bargains, for example. Equally they may just take long term contracts with suppliers who themselves do the bargain hunting. Either way batches could vary around a minimum spec.

The crude oil varies quite a lot.

 

[kbekl]

my w124 gets more mpg when using premium fuel over normal

also i have noticed a increase from using bp ultimate and v-power tend to get more using v-power (and i live in cornwall everywhere their tends to be steep hills)

 

[stevieb15]

There have been independent tests showing bhp and torque increases with 'premium' fuels (compared to standard fuel, checked on a dyno). But this benefit isn't universal - it depends to some extent on the specific car and engine. So it's not possible to make any simple statement like 'gives x% more power'.

I know that Shell Optimax (and then V-Power) made a difference in my V6 4Motion Sharan because:

a) when towing the caravan, 6th gear was basically unusable on standard fuel but OK on the premium stuff (more torque)

b) repeating the same cross-Europe run using different fuels I consistently got more range on premium fuel (making the "one fuel stop" strategy comfortable rather than nail-biting!).

Do you have anything on the impact on the SL500

 

[BTB 500]

Do you have anything on the impact on the SL500

No.

I do use V-Power in mine, but this is because I genuinely believe it's a 'better' fuel (in terms of the cleaning agents etc.) rather than trying to get more bhp/torque or range. It also does low mileage, so the extra cost isn't a major factor.

You'd have to dyno it before/after (with an ECU reset in between) to know if there was a performance gain. I don't think anyone would notice (let's say) 5% more power in normal driving.

This is one of the tests I was referring to (98 RON Shell Optimax now replaced by 99 RON V-Power):

Page 1 features - Fifth Gear

 

[acm718]

We used to have a Smart car, that was remapped, from memory, to a heady 80bhp.
Optimax as it was then made a huge difference to the drive of the car, to the point I wouldn't put anything else in it.
Very noticeable, and I wouldn't say I'm a driver in tune with an engine well enough to notice an extra few % power on a more 'normal' car.

On that basis, I've always put 99ron Tesco or V-Power in my Alpina, as they recommend super unleaded only, but in theory it'll retard the timing to cope with standard 97ron.
I can't feel a difference between V-Power and 99Tesco.

Merc will get standard unleaded, but I try to avoid supermarkets - that Morrisons fiasco a while back made me paranoid about poor quality fuel.

Another point is I think fuel deteriorates with age, losing it's 'rons' - so if you have a sunny-day/once a week/month car, keep it very low on petrol and top up frequently, or use high grade fuel that may stay at or above 97ron for longer.