GEAR | Need Oil For Your Old Car? How To Choose The Right Type

How do you choose which brand of oil you put in your old car? Just picking up the first 20w50 you lay your hands on is probably not the right answer, especially given that different cars are used in different ways. Is there a simple way of deciding on how to get the best value for your money?

Assuming that 20w50 is correct for your car you could pay anywhere between £12 and £51 for 5 litres. I've never had a very scientific way choosing oil for my cars so invested a bit of time recently reading the excellent book Which Oil. It goes into detail (maybe too much!) about how best to choose oil and grease for vintage and classic cars. This is my very distilled version of the discussion in the book. I think the best decision making route involves taking three things into consideration; the viscosity specified for the particular engine, the oil API classification (other classifications are also used) and the way the car is driven.

The easy bit should be deciding what viscosity is right for the car - read the manual! Stick with this and don't choose an oil with a lower classification than specified. Ambient temperature will play a key part in getting the viscosity correct.

Next is the API engine oil classification. This was introduced in the USA in 1971 and has been used to monitor and specify the quality of oil ever since. It ensures that oil technology keeps pace with the engine technology. The ratings range from the lowest at SA through to the highest at SN. For the sake of this I've used the simple classifications used in Which Oil, these are; Modest = SG, Moderate = SJ and High = SL/SM/SN.

Now think about how the car is used. Is it a track-day car, a shopping car, or is it just used on high-days and holidays? Advice from the experts is to think along these lines;
  • A few short trips a year - MODEST grade oil. Change every 3 trips or 12 months
  • Semi-regular use (short or modest trips) - MODERATE grade oil. Change every 6 trips or 12 months
  • Regular use - MODERATE/HIGH grade oil. Change every 3000 miles or 6 months
  • Irregular but stressful use (e.g. road rally or track-day) - HIGH grade oil. Change after every event!
So now you know the viscosity you need and the suggested API grade. With that you can now look at what is available. I'd suggest always going with a well established manufacture and looking at the best price for an API grade. If you keep to the oil change routine suggested then the higher price synthetics will not provide a real advantage. Look at the graph and see what the best value oil is for a the specification needed and the choice is yours.

That was easy enough wasn't it? If you've been through a few engine rebuilds like me, then you'll know this makes sense...

Prices are for guidance only, from the excellent Classic Oils people, Halfords and Opie Oils

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