DTCwordfan
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tony in the States, Shell and Chevron have been claiming at least 5% fuel economy on their gas (petrol), the results coming into the research centres in order of 10%, some above that too, but then the lawyers want conservativeness in claim......
why, because the detergents help keep the tar down and also aid the ignition at the top of the cylinder head, thereby minimising the risk of knocking..... with the price of petrol at around 43p net of excise duty and tax, then this represents some 3 to 4p a litre on UK fuel......
Good lub condition helps as well by the way, and I'm sure that you know that.
I understand what you mean, DT. Besides good lube condition there are other factors, tyre pressure and weight inside the car being some.
The Americans seem to be tightening up on car manufacturer's exaggerated MPG claims now.
http://www.msn.com/en-gb/cars/news/hyundai-and-kia-in-record-fuel-economy-settlement/ar-BBcUSz2