If you look at the Owners Manuals recommendations you'll see: SAE 10W40 for S4, 748R, ST (from 2002) 998/748 (2002) All newer bikes but still with old engine designs. SAE 20W50 for 748/996, ST, (up to 2001) All older bikes If you look at the Manuals temperature to viscosity chart, it is identical for all bikes so that has not changed but the recommended viscosity has changed. It could be because some time ago Ducati was sponsored by AGIP and they sold 20W50 oil. Now sponsorship is Shell and they sell both 10W40 oil and 20W50 oil. ST4 and S4s engines are more or less identical except for camshafts and the S4 does not have an oil cooler. This means that the oil will run hotter in a S4. Still, Ducati recommended 10W40 for the S4 and 20W50 for the ST4; maybe they were too lazy to update the manual for the ST4. The more interesting is the 748. When it was later included along with the 998 in the Manual, it suddenly went from 20W50 to 10W40 without any changes to the engine. |