Who says all fuels are the same?

I've often noticed a lack of "go" with Tesco and Sainsburys fuel. It wasn't psychological because I wasn't looking out for something to be amiss so I can only assume that, for some reason, the octane is lower.

Si

The message from "James" contains these words:

Ah, well, that's your penalty for not being an average driver.

If someone delivered fuel to you and you didn't know which was which - you wouldn't notice anything. You only see a difference because you want to. I would like to see proof of what the difference in composition of different fuels is - I assume you have that ready to post?

Yes.....*pondering*.....but there did seem to be a marked difference...

I haven't used any supermarket petrol for yonks now.

Si

This is only true if you are *expecting* a difference, like with Optimax for example. In my case I wasn't expecting supermarket petrol to be any different but it definitely was.

Si

I haven't used Shell petrol for years now - not since I got a pint of sludgy water in my tank.

My wife has always said that Tesco petrol runs better for her and seems to give better mpg. I always refuted her claims and said that the local Texaco was better, that was until I tried Tesco diesel and I found it better - no noticable performance difference at all but seemed to offer better mpg (run to work on Tesco was 55 mpg cf Texaco @ 49 mpg).

Andy

Both Tesco and Sainsbury sell 'City Diesel' rather than the normal Ultra Low Sulphur Diesel (ULSD). City Diesel has gone through further refining process to further reduce traces of impurities. While they claim there is no difference in performance, I just wonder if City Diesel has a touch lower energy content than regular diesel. You notice you get better MPG and throttle response with French diesel, because the fuel has around 2.5% biodiesel content.

Alec

Octane? It's a smokey oil burner!

-- Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!

The message from Peter Hill contains these words:

And anyway - we did this two days ago - the octane number isn't the energy content or the "power" of the fuel.

My Sainsburys which I use when I can (on the way to the motorway) has not risen above 79.9p for petrol this year, making it 4-5p cheaper than other stations locally, currently 78.8. It gets filled by a BP tanker. I can tell no difference in any of the petrols - I guess knock sensor per cylinder, VVT, turbocharger, electronic injection and closed loop monitoring will do that for a car. Optimax is noticable but as there are only two places I can get it within 20 miles of me and it's dearer, I don't bother any more other than using it in MOT month as an injector cleaner!

So 'tis, beg pardon. Even so...Tesco petrol...*waves fist* :o)

Si

I never use the local Tesco fuel as the queues are so long! Years ago I thought small 2 stroke engines I had at the time worked better on 5 star than the lower star rated fuels, but I never proved anything. My current Mk1 Punto seems to run much the same on anything, and there is no obvious advantage to the more expensive fuels in that. I use Shell or BP as the garages are convenient to my usual routes. However, one engine I had a couple of years back was rather more indicative. It was a tired old Reliant engine, which burned a fair bit of oil. The compression ratio was 9.5:1. It pinked and rattled like a pig (pun intended) on 4 star. It had an unleaded proof head so I tried Optimax. When it was running on a high proportion of that, it was almost impossible to get it to pink. This alone allowed improved performance and made it a lot easier to use. No improvement in economy, for that reason if no other! I assume this was mainly due to the higher octane rating, but it certainly worked in that engine. Worth a few pence a litre to make it drivable. With computer controlled injection rather than a rattly old carb the advantages may be less pronounced!

I've got an SD1 Rover with EFI. It was designed for 4 star. The EFI is open loop, and has no control over the ignition, which is conventional for its time - ordinary centrifugal and vacuum control.

On 95 octane, it pinks - and badly. Runs beautifully on Optimax. Seems also to prefer Optimax to BP Ultimate, but that could just be coincidence.

Honest John hasn't got a good word to say for supermarket petrol - don't know about diesel, though.

Rob Graham

I also have a KTM enduro bike, which has a 400cc 4-stroke engine optimised for racing. On ordinary petrol it pinks something terrible at low revs, and vibrates a lot at high revs, but on optimax or super unleaded it is muted and smooth, and accellerates *much* quicker. The manufacturer simply states a minimum of 95RON though.

I've never noticed any difference in a modern car though between different petrols. My old mk2 cavalier though (a long time ago) pinked on Tesco and Esso petrol, but BP and Shell were fine.

But never mind, I'll be back to Shell derv in a week or two; The price is now the same as Tesco again :-)

James

Optimax has a higher RON...

I thought refuting an argument required evidence?

-- Malc