There is a Fiat document somewhere which iirc says that the X1/9 can run on unleaded but that additives may be needed to avoid damage under " prolonged high speed running"
I found that mine ran much better on Shell optimax (especially with the ethanol levels rising in std fuel) and used Shell Valvemaster additive whenever I was planning a long slog along fast roads.
Been reading some interesting article on the MG T series website and the issues modern fuel causes in old classics. While our cars may not be as badly affected as theirs it has proved to be an interesting read, I’ll see if I can get the links up.
I use 97 Ron where I can and think I’ll experiment with a little 3~5deg more advance as it seems this can help in keeping exhaust temps down and preventing a weakened mixture.
One very interesting find with ethanol fuels is they are much more volatile than none ethanol fuels meaning they vaporise at much lower temps causing bad running and hot start issues. Glad our cars have a carb coolling fan!
Acknowledgement to Paul Ireland of the MG T-Type club (
ttypes.org/ttt2/
) for these excellent articles on classic engines and modern fuels.
Whilst the test subject revolves around the XPAG engine and modern fuel, some very interesting facts emerge from these articles that readers may find useful. I certainly want aware of the move to Ethanol 10% based fuel or the variability summer/winter in supply of petrol throughout the year. Hope you find the articles as interesting as I did.
For those interested Esso 97 octane fuel contains no ethanol depending on which region you are in,,from their FAQ:
“Esso super unleaded petrol (Synergy Supreme+ Unleaded 97) is ethanol free (except in Devon, Cornwall, the Teesside area and Scotland). We would therefore advise anyone who has concerns about the presence of ethanol in petrol to use Synergy Supreme+ – providing they do not fill up in Devon or Cornwall, the Teesside area or Scotland.”
In my archive I’ve a letter the original owner wrote to fiat asking about this. The reply wasn’t convincing and so it was only run on leaded 4* until I had it 12 years ago. Since then it’s only been run on shell v power. And it runs very well averaging over 40mpg.
1988 SE in mica blue
1985 Citroën 2CV6
2021 Fiat TIPO Cross
The Federation of British Historic Vehicle Clubs has a list of fuel additives which they've tested.
They also have a list of the very few places where you can still purchase 4 Star leaded petrol.
Fuels, additives & 4 Star
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