Super Market Fuel

[harrypotter:)]

Recently I filled up with cheaper fuel from Asda. At the present time it is giving me the lowest MPG I have ever had 45.5 on my Gen 2 T spirit. Maybe it is the colder weather only +3 today. Does any other Prius owner experience lower MPG with cheaper super market fuels?

With my Avensis I was told by the dealer it is OK to use the cheap fuels but every so often put the very best fuel you can in the tank. When I purchased the Prius dealer said just use any low octane fuel. ???

[harrypotter:)]

waitrose fuel gave me 4mpg extra when i had my avensis 1.6 i returned to tesco fuel several times and this confirmed waitrose is much much better and the SAME price per litre in my area aswell. Pumped marked up at waitrose as PREMIUM unleaded i class premium better qaulity than unleaded or regular unleaded i may be wrong but my aygo is running on waitrose fuel and getting 63.6mpg country lanes/dual/town driving 410miles per week. Wont bother trying out any other fuel stations as im happy with this figure. Waitrose swaffham norfolk £127.9 per litre super is only 3p yes 3p dearer so may try this out

[Opifex]

Can't add much except that my old Saab was smoother and more responsive when running on Shell V Power instead of normal branded 95.

If you are planning going on the continent with your Prius this summer I would recommend that you avoid filling with SP95-E10 (10% ethanol) fuel which is now replacing normal 95 octane on some forecourts in France. I used one tank and the car was very sluggish, struggled to get up hills on the motorway and the consumption increased. When I stopped and filled up with normal 95octane the car went romping up the next hill with no problem and the mpg figure increased by about 5mpg.

[britprius]

Using 99 octane fuel in a Prius will give lower MPG, this fuel has a lower callorific value than 95 octane and will produce less power in an engine that is not designed to run on it.

[Grumpy Cabbie]

In theory but then again the Yanks use 91 octane (87 on US scale) and they object to using 95 octane (our normal unleaded) as they say it gives less mpg's. Weird as we seem to get the same mpg's as they do (even accounting for their smaller gallon at 3.7 litres compared to 4.5 litres for ours).

Perhaps the car adjusts for the different fuel using knock sensors etc?

[Cyker]

Cod air does tend to cause an increase in fuel use in petrol engines due to the whole colder air = higher air density thing, but if that was the only reason then my diesel lump wouldn't be affected at all (The accelerator in a diesel controls fuel flow rather than air flow throttling as in a petrol engine).

The main reason for the mpg loss is because the engine block takes much longer to warm up to its most efficient operating temp range in cold weather, and as soon as you get stuck in slow traffic and idle it cools down again. My Yaris really hates the cold as it generates sod-all heat unless I thrash the nuts off of it, so in the winter I'm usually freezing my nuts off!!

The Prius is particularly vulnerable to this because its petrol engine is (Under normal circumstances) never run long enough to remain at optimal operating temperature for a decent amount of time.

But this is why you see taxi drivers sticking a whopping great hunk of cardboard over their radiator grills in winter, so the car heats up faster and stays heated up so the engine runs more efficiently. :)

As for fuel, I have found V-Power Diesel particularly crap in cold weather unless you're hitting motorway speeds. I went back to normal diesel last week (Sainsburys 'City diesel' ) and am getting better mpgs for urban driving than I was getting with V-Power.

V-Power really doesn't work for me unless I'm doing 1800rpm or more (Then it's great ) but when driving off-turbo (Which is what you want for maximum efficiency!) normal diesel seems to be deliver noticeably more torque which lets me abuse the high gears without labouring the engine :). I still haven't tried Shell's Fuelsave Diesel yet tho', mainly because it's 5p more than my supermarket fuel :(

[britprius]

The water is muddied a bit in the USA because of the use of alcohol in the fuel and yes the prius does adjust ignition timing via knock sensors if you use a fuel that is below spec, but if you go above spec no knock from the engine and it runs at the timing pre set by Toyota and will not advance the ignition to try to take advantage of higher octane feul.

[Grumpy Cabbie]

But a lot of our fuel has various amounts of ethanol in it and I think that's where some of the differences occur between 'normal' and some supermarket blends. I'm sure I've read somewhere that there are different British Standards for the differing petrols with differing ethanol amounts in it. Does anyone with knowledge know if this is true?

[britprius]

A few petrol stations carry E/blends but they have to be clearly marked as it can damage some engines. The EU has decided that by 2013 all fuel must contain 5to10% ethanol i pity people with metal fuel tanks as ethanol is corrosive.

[Ancient Nerd]

I've just had a look at my fuel consumption for the last few months, compared with the same few months a year ago. It has improved by 2-3 mpg. This included December, which was colder than the previous year, so I would have expected consumption to be worse, not better.

As far as I can see, there are three possible reasons:

• The car is now very well run in. 30-40,000 miles against 0-10,000.
  
• I started using my own oil (Motul 0w-20 from Opie) instead of Toyota 0W-20.
  
• I've been using Shell Fuelsave petrol since it was introduced.
  

Timings suggest the oil. I don't think it's the garage using 5W-30, and charging for 0W-20. The mpg change isn't big enough for that.

I don't think it's the running in. I didn't have the same improvement with the old Gen II, with very similar mileages involved.

The improvements kicked in about 2 months later Shell introduced Fuelsave. So either it's not that, or it takes a couple of months (4-5,000 miles) for it to really kick in.

However, my son who is now driving my old Gen II (85,000 miles) has noticed a distinct improvement in mpg after changing from Tesco to Shell (new jobe, no longer near a Tesco filling station), with the engine apparently running more smoothly. He thinks more than enough to justify the loss of Tesco points.

FWIW. As far as I know there is no difference between brands in the underlying petrol. There can be a big difference in the additive package. I know that Shell does a lot of research to develop these, which is why I use it most of the time. The other oil majors are probably similar, while the supermarkets and others rely on whoever supplies their fuel - and even if they buy from a major, they may not get the same additive package.

[Grumpy Cabbie]

It's the oil!

If the garage used 5w30 then it hammers your mpgs (gen3 Prius only).

Don't believe me, check out some of my earlier posts from about a year ago. When they used 5w30 by mistake I couldn't get past 55 mpg unless I really really tried hard. When I use the correct 0w20 I can get 75 or 80 mpg for long periods such as in a 50 mph motorway works zone.

[johalareewi]

... I can get 75 or 80 mpg for long periods such as in a 50 mph motorway works zone.

Those motorway roadworks are great for giving an mpg boost

[Ancient Nerd]

It's the oil!

If the garage used 5w30 then it hammers your mpgs (gen3 Prius only).

Don't believe me, check out some of my earlier posts from about a year ago. When they used 5w30 by mistake I couldn't get past 55 mpg unless I really really tried hard. When I use the correct 0w20 I can get 75 or 80 mpg for long periods such as in a 50 mph motorway works zone.

I believe you alright. The problem is that the comparison is with the first 10,000 miles, when the car was using the original factory fill oil, so it's unlikely to be a rogue factory fill of 5W-30. And it was filled by Toyota Japan, so no opportunity for Toyota GB to mess up! Also, I'd have expected a bigger improvement if it was the oil.

I would have said it was because the car has now been thoroughly run-in. However, there was no similar jump with the Gen II. Or is it that the GenIII runs in better than the Gen II?

[Grumpy Cabbie]

The engine in the gen3 has higher tolerances and needs the thinner oil. See other posts- Toyota UK even sent a mail round all dealers saying they MUST now use 0w20 as previously they said they could use 5w30 in certain circumstances for a temporary period.

If you doubt its got 0w20 in it then get the dealers to change it - maybe say you'll get in analised. Mine changed it half way through as I told them about the running issues (shown below) and though the oil was over filled. They changed it back to 0w20 and the problems stopped immediately.

The way I knew it wasn't 0w20 was that the car was much much quieter at cold start (5w30 is thicker), it was hesitant when the engine fired up (even when warm) and there was no power in Power mode. Also the mpg's were about 50-55 mpg at best. Went back to being a fabulous, smooth and very economical car once the correct oil was back in.

Let us all know how you get on.