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Date: 15 September 2014

Today's Topic: Petrol Quality

Triggers: Personal Experience

My Grump: Cheap is never the same as quality

I'd never have believed this if you'd told me, or I'd read it in a report. But I believe it now, because in the last 6 years I've been running tests.

In that time I've heard numerous reports of supermarket petrol being rubbish and full of detergent and fillers. That's how they keep the prices down. We even had one garage near us closed and fined for putting unleaded in the super and charging more. Thank goodness Trading Standards keep an eye on such things on our behalf.

I didn't believe it because I mistakenly thought, they wouldn't take that chance, would they? But after Tesco's and other supermarkets horsemeat scandal, it seems anything goes to keep prices low. How wrong could I be and how wrong I was?
petrol pump dispensers
I used to use ANYBODY's fuel. Meaning, when I was getting low, I'd drive into the first garage on the left and fill her up. 'Her' is a beautiful Mercedes S class S280, so she ain't the cheapest car to keep on the road by any means.

When fuel broke the pound barrier many years ago, the sky was the limit as far as fuel prices was concerned. Until that time, the pound a litre was a bit of a ceiling that none of the producers or sellers seemed to want to go near. Blimey, I can remember it being 1/3 a gallon old money, or 1 shilling and 3 pence (1s/3d). This would now be about 7p a gallon in todays money.

Sorry, I digress. I started filling up when we did our shopping at the supermarket, mainly because of price. It got to the point that I begrudged the huge profits of the oil companies, when in reality it is the sneaky tax hikes of the government that was really driving the price up. I found I was having to top up more and more often.

For a while I took no notice, probably thinking, 'ya lazy sod', you're driving more rather than walking or combining trips. But the mileage was staying roughly the same. And, I still didn't twig.

What changed was that I absolutely HATE QUEUING with a vengeance. As the queues in the supermarkets were getting longer and longer, driven by the price of fuel and the bloody offers of, spend 50 and get 5p off a litre, I began to see 20mins in a queue as time ticking away that I can't get back.

When I finally did the math, I discovered that the car was only doing 22 - 23 mpg. I wondered if there was something wrong with the computer, the carburetter or the lambda or something else, because up until then I would normally average 25 - 26 mpg. Now don't get all environmental on me, OK? I'm a big guy and I need a big car. Driving around in a bleeding 'buzz box' is not my idea of fun, cheap or not.

Anyway, I started going back to the independent garages, which are usually around 4p a litre more than the supermarkets. In my view, a small price to pay for not having to queue. To my astonishment I noticed that the mileage per gallon went back up to 25 - 26 and even 27 mpg. Now, 3 more miles to the gallon means that a gallon of unleaded is now 20p more than the supermarket, but I'm averaging 3 more miles on the same fuel.

3 of 26 is a 8.6th or 11.5% greater efficiency per gallon. 4p of 127p is a 32th, or 3% more than the supermarket price. One gallon at 1.27ltr = 5.78 per gallon.

The point being here, it's actually cheaper to buy the dearer fuel by quite a large margin.
petrol pump dispensers
I decided, one day, to give the car a treat, and as it was nearly empty, filled it up with Super Unleaded. I thought, why not? A good, high octane fuel once in a while won't hurt the engine none and will probably do it good. WRONG!!

The first tank of high octane was a disaster. The car made funny noises, it lunged about and behaved in a really odd way. I decided this was not a good idea and when it ran out went back to the other stuff. In the meantime, I asked a few questions on the Mercedes forums to find out other peoples experience of this. Apparently, the onboard computer makes adjustments for the fuel mixture and other parameters for how the fuel interacts with all parts of the engine. These adjustments occur over time, or a pattern of driving and the conditions, and are not instant. Their advice was to try again, but for longer.

This I did. To my astonishment, the car started to handle much better. It was more responsive, quieter AND I began to rack up distances of up to 32 mpg. Admittedly, this fuel is 5p and sometimes 6p a litre dearer than even the independent stuff. But I've again gone up from 26 - 27 mpg to 31 - 32 mpg.

I find this quite remarkable! Almost a 10 mpg hike from the supermarket rubbish. Admittedly we are now talking about a price difference of around 10p a litre, or 45p a gallon. But when you think the mileage has gone up by almost a third for what is essentially a 12% increase in fuel cost.

Or, to put it another way. To get 32 miles on supermarket fuel, I have to put in the best part of a gallon and a half; not quite, but say around 7.60 of fuel, when supermarket price is 1.23 ltr or 5.60 a gallon. High octane fuel at 1.35 ltr or 6.15 a gallon, for the same distance, is very much cheaper in the long run.

It is clear to me now that there is a very marked difference in fuel quality in the market place and the supermarkets are not doing you any favours whether the cheapest, or not.

The rule to bear in mind here is: Computers like the good stuff! (eventually)

Please share your thoughts below, thank you.

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