Originally Posted By: miami993
Originally Posted By: 3311
I'm not much for boutique oils but Redline 5w50 for your application:
http://www.redlineoil.com/product.aspx?pid=135&pcid=21
Mucher HTHS than the Mobil 1 15w50 and RL 10w40.
Originally Posted By: A_Harman
If you're searching for a direct replacement for M1 15w50, which has an HTHS of 4.5, Redline 10w40 is almost identical at 4.7, and their 5w40 is 4.6. RL 0w40 is a bit wimpy at 4.0. The Redline 5w50 is a monster oil with HTHS of 5.9. Unless your engine has a serious problem with fuel dilution, I don't think you need an oil that thick.
Is the HTHS number the determining factor in the "bearing help" process?
Mobil 1 0W40 HTHS 3.6
Castrol RS 10w-60 HTHS 3.7
Castrol RS 0w-40 HTHS 3.7
Silkolene PRO S 5w-40 HTHS 4.07
Motul 300V 10w-40 HTHS 4.19
Motul 300V 5w-40 HTHS 4.51
Redline 5w40 HTHS 4.6
Redline 10W40 HTHS 4.7
Mobil 1 15w-50 HTHS 5.11
Silkolene PRO S 10w-50 HTHS 5.11
Silkolene PRO R 15w-50 HTHS 5.23
Motul 300V 15w-50 HTHS 5.33
Redline 15W50 HTHS 5.8
It is how "heavy" the oil is in the bearings. Most Euro marques shoot for an oil with an HTHS >3.5cP. This is why oils like Delvac 1 5w40 and M1 0w40 are popular choices.
Your engine, stock, spec'd an oil with an HTHS of ~3.0cP. Any of the oils we are discussing are notably heavier here, and heavier than the spec oil for the ZL1 'vette too, which is your basic ~3.0cP HTHS synthetic 5w30.