- 1956 Citroen Traction Avant SAE 20 ("All temperatures")
1962 Haflinger SAE 30 (0c <> 30c) or SAE 10w30 (< 0c)
1964 Mercedes 230SL SAE 10w40 or SAE 10w50 (-20c <> 30c). Not sure why two are given. (For 0c <> 10c, SAE 20w40 or SAE 20w50 is suggested, and in reality I never use the car in sub zero temps)
Seeing as "20" and "30" both sit between the range "20w50" would it be possible, realistic, or "right" to use just the one multigrade oil, or am I missing a key aspect of understanding oil specifications?
Or do I owe it to myself to just buy three grades and use the specified one in each machine?
[EDITED TO ADD: I see that Steve's recommended Valvolene VR1 20w50 is available in the UK; it costs ~GBP 30 inc VAT for 5 litres, which isn't cheap ]