Single-grade engine oils for vehicles of the 60s, 70s and 80s
HD "Heavy Duty" oils are used for vehicles with oil filter built from the 60s onwards. Single-grade oils because they are filled either in summer or in winter, depending on their viscosity. Vehicles driven in winter time, need a low SAE Class (e.g. SAE 10), thus a highly fluid oil. Engine oils of a higher SAE Class (e.g. SAE 50) are more viscous, they are used in summer time. You should, furthermore, pay attention to oil loss.
Please note: Every rule has its exception. If you are not sure, you can get advice by filling in our form.