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I'm unsure if my 1982 Ford Sierra was converted to unleaded - should I run it with lead additive or on unleaded petrol?

I recently returned to the road my 1982 Ford Sierra 1.6 (petrol, pinto, manual) I believe it came off the road in 2002 or earlier, long before I purchased it, and I'm unsure whether or not it has been converted to unleaded. One friend suggested simply running it on 98 Octane fuel, another suggestion I’ve heard is to run it on standard cheap supermarket fuel with a bottle of Reddex lead additive. Which would you suggest? All I have found locally is 99 Octane (AKA Tesco Momentum), would this suit?

Asked on 21 August 2018 by Sean G.

Answered by Keith Moody
Ford began shifting their OHC engines to run on unleaded fuel in the late-1980s. Sometimes, they have M, MM, N, or NN stamped on the head at number four spark plug to identify this. With lead removed from fuel, older engines suffer from valve seat recession. If you can't contact the previous owner or have no way of checking, the question you need to ask yourself is how many miles you plan to do in the car? If you're only planning to do 2000-3000 miles a year, then simply running an additive in the fuel will suffice and protect against the damage to the valve seats. If you choose an additive that has an octane boost, you shouldn't suffer any negative effects on ignition timing (or if you do, it will only require minimal adjustment).
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