From here: 


Received via email on Sep 7 [2006]



Thank you for your further e-mail.

VW 50501 was newly introduced in July 2005.

VW 50501 is not based on VW50500, but represents a higher quality level.

Since July 2005, VW 50501 is only proved in connection with VW50200.

VW 50501 includes VW 50500, because the requirements towards VW 50500 are also

completely fulfilled by the VW 50501 oils.

According to VW 50501 0W-x, 5W-x, 10W-x, xW-30 and xW-40 are permissible.

Up to now, we have only approved oils with the viscosities SAE 5W-30 and 5W-40.

Best regards
So, VW 505.01 (the normal drain interval standard for PD TDI engines that don't use diesel particulate filters) was introduced in 2005-07. It is not based on VW505.00 (the normal drain interval standard for all diesels that aren't Pump-Düse or the Touareg V10 TDI) but is a higher quality superset of it. Before on oil can meet VW505.01 it must meet VW502.00. Originally, only 5w40 synthetic oils were approved, but now 5w30 oils have been approved, too. VW505.01 allows 0W/5W/10W-30/40 oils viscosity oils.

In other news, HTHS viscosity is a measure of viscosity breakdown under high-temp/high shear conditions. The higher the number the better the oil protects against wear, but beyond a certain point you'll take a fuel economy hit. VW505.01 requires a minimum HTHS viscosity of 3.5 cP (centipoise). SAPS measurements relate to the levels of sulphated ash and phosphorus in the oil. High ash is bad for diesels that use DPFs, but the higher the SAPS number the better the oil protects against wear. NOTE: The extended drain interval standards (VW506.xx) actually call for a maximum HTHS because they focus more on maximizing fuel economy.