Ask Honest John

Most recently answered performance fuels questions
Can you advise, my Porsche has 98 octane fuel printed on the filler cap. This is not always available and I use 95 Octane without any discernible effect, then filling the tank with 99 octane now and again...
I've recently seen you advise using Shell V- Power because it improves performance and mpg. We don't have a Shell garage here, but we do have a Tesco station which sells their premium brand, Momentum,...
I own a Volvo 960 and the lambda warning light keeps coming on. My local garage reset the system, but the light came back after 100 miles. Any idea what's causing this?
Premium diesel is about 70p more per gallon and one of the additives used to formulate it is detergent. Would it be a good idea to add washing up liquid to standard diesel?
I have just bought a used Ford Focus (2015 model) with the petrol EcoBoost engine. The dealership said they recommend using super unleaded. Is there a reason for this or is it just sales talk?
I have a new Jaguar F-Pace. Is it worth buying branded diesel,rather than supermarket fuel? If so is premium worth the extra?
I gather that you recommend Shell V Power Nitro Plus petrol, but as Shell garages are thin on the ground in my parts, are there any other suppliers' super unleaded brands of equivalent quality?
Having just sold my 2004 BMW 330 convertible to a family member after seven fault free years, I intend to replace it with a 328 Touring on my budget of £20k when I can find the right car. In the meantime...
We've always used Shell V-Power Nitro + in our DS3 DSport plus. Next week we are changing it for an Hyundai i20 1.0t, should we continue to use the same fuel?
I have noticed a considerable difference in mpg when using some supermarket fuels compared to Shell V-power. Is this due to supermarkets buying low grade fuel to keep their costs low ? What is exactly...
 

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