From the Shell Rotella Fourm:
http://www.shellusserver.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=3323&page=5&fpart=2
"Someone over on BITOG e-mailed Shell about this. Here is the reply he got:
I show that typical values are 4.1 for Shell Rotella T Multigrade Oil SAE 15W-40 with Triple Protection Technology and 4.2 for Shell Rotella T Synthetic Oil SAE 5W-40.
Thank you for your interest in Shell Rotella Products!"
A HTHS rating of 4.1 and 4.2 sounds about right when compared to other CJ-4 or CI-4+ rated oils.
Below are HTHS ratings that were pulled of the corporate websites of the various oil companies.
Amsoil Series 2000 20w50 (API SM) – 5.8
Amsoil Premium Protection 20w50 (API SL) – 5.0
Amsoil Marine Synthetic 10w40 (API SL) – 4.6
Mobil 1 EP 15w50 (API SM) – 4.6
Pennzoil Marine SAE 40 (API SJ) – 4.5
Mobil 1 15w50 (API SM) – 4.5
Amsoil Heavy Duty Diesel 15w40 (CI-4+) – 4.4
Amsoil Premium Protection 10w40 (API SL) – 4.3
Amsoil XL 10w40 (API SM) – 4.3
Pennzoil Truck/SUV 15w40 (CI-4+) – 4.3
Pennzoil Long Life Heavy Duty 15w40 (API SL) – 4.3
Amsoil Premium Diesel 5w40 (CJ-4) – 4.2
Mobil 1 High Mileage 10w40 (API SL) – 4.06
Pennzoil Marine 15w40 (API SL) – 4.0
Amsoil European 5w40 (API SM) – 3.7
Mobil 1 High Mileage 10w30 (API SL) – 3.66
Amsoil Marine Motor 10w30 (API SL) – 3.64
Mobil 1 0w40 (API SM) – 3.6
Amsoil Heavy Duty Diesel 5w30 (CI-4+) – 3.5
Pennzoil Long Life Heavy Duty (API SL) – 3.5
Pennzoil Marine SAE 30 (API SJ) – 3.5
Amsoil Signature Series 0w30 (API SM) – 3.2 (meets GM Standard 4718M)
Amsoil SAE 10w30 (API SM) – 3.2 (meets GM Standard 4718M)
Amsoil SAE 5w30 (API SM) – 3.2 (meets GM Standard 4718M)
Amsoil XL 5w30 (API SM) – 3.2 (meets GM Standard 4718M)
Amsoil XL 10w30 (API SM) – 3.2 (meets GM Standard 4718M)
Amsoil XL 5w30 (API SM) – 3.2 (meets GM Standard 4718M)
Pennzoil Platinum 10w30 (API SM) – 3.15 (meets GM Standard 4718M)
Mobil 1 10w30 (API SM) – 3.14 (meets GM Standard 4718M)
Mobil 1 EP 10w30 (API SM) – 3.1
Mobil 1 EP 5w30 (API SM) – 3.1
Pennzoil Platinum 5w30 (API SM) – 3.1 (meets GM Standard 4718M)
Pennzoil Truck/SUV 10w30 (API SM) – 3.1
Mobil 1 5w30 (API SM) – 3.09 (meets GM Standard 4718M)
Mobil 1 Truck/SUV 5w30 (API SM) – 3.09
Pennzoil Truck/SUV 5w30 (API SM) – 3.0
Mobil 1 0w30 (API SM) – 2.99 (meets GM Standard 4718M)
Amsoil SAE 0w20 (API SM) – 2.8
Amsoil XL 5w20 (API SM) – 2.7
Mobil 1 EP 5w20 (API SM) – 2.7
Mobil 1 5w20 (API SM) – 2.62
Mobil 1 0w20 (API SM) – 2.61
Pennzoil Platinum 5w20 (API SM) – 2.6
Pennzoil Truck/SUV 5w30 (API SM) – 2.6
Pennzoil Platinum 0w20 (API SM) – 2.6
Note: Many companies such as Castrol, Shell, and Royal Purple do not list HTHS ratings.