17th November 2020

Ask An Expert: Can I Drive My Classic With Stale Fuel?

In this edition of Ask An Expert, we sought to find the answer to Roger Teare's question on stale fuel:

I own a 1956 Series 2 Morris Minor, though it now has the later 1098cc engine. It was the first car that I used on the road, back in 1972. It has not driven far in the last 10 years, so the fuel in the tank is 10 years old. Before March 2020 it did go for occasional drives, for fun & just to keep it workable. It did seem to need more choke for starting & achieved less manifold depression when idling or cruising. Up to 3000rpm it seemed 'Minor like', but quite reluctant to rev more. This might sound in keeping with the 'old fuel' symptoms. My question is, when the ambient temperature is higher and fuel vapour pressure is higher & viscocity lower, would you expect it to work less badly with old fuel?

We spoke to Alan Scott, Technical Advisor at the Morris Minor Owners Club. He thinks that Roger's stale fuel could be affecting the performance of his moggy. Roger could:

  • drains the old petrol
  • replaces with fresh petrol
  • adds in some Redex and lead additive
  • then take it for a good run!

This would be similar for all classics, not just Morris Minors and Alan opinion is owners don't leave petrol older than 2 years in the car.

We also got in touch with Morris Minor specialists Charles Ware, who also recommends draining away the old the fuel. The fuel can be drained into a fuel can via a bung in the bottom of the tank or via the electric pump. They did stress though that it's important to then dispose of this fuel legally, so it may be more convenient for a local garage to perform this task for you.

Fresh fuel has been a hot topic on Ask An Expert in recent months. For further advice, take a look at our blog, Ask An Expert: Should I Fill My Tank With Fuel When I Store It?

If you have a classic question you would like answering by an expert, simply complete our Ask An Expert form and we could be answering your question next week.

The information contained in this blog post is based on sources that we believe are reliable and should be understood as general information only. It is not intended to be taken as advice with respect to any specific or individual situation and cannot be relied upon as such.

I was pleasantly surprised to see that FJ had looked into my 'old fuel' question. Are you any nearer answering my actual question re the expected effect of warmer weather on performance? I can add, from a small, recent experiment, that cold starting is dramatically improved by warming the fuel pipe between the float bowl & the jet on the SU carburettor, to 20C. From that, I'm in no rush to discard a tank of fuel.

Roger, 19/11/2020