I have been studying 0w and 5w-30 oils a little that have a 3.5 or higher HTHS value. So far, I had this reply back from Castrol USA. I sent the same request to Mobil and Pennzoil/Shell, I am waiting for replies from those two yet. Some that I already know of are Kendall GT-1 Max Euro 5w-30 with 3.6 HTHS and a couple Liqui Moly products, their 5w-30 Top Tec 4600 and their Top Tec 4210 0w-30 both which are >3.5 HTHS. Motul has 8100 X-Clean+EFE 0w-30 with a HTHS of 3.5. Anyhow, I will post what I got from Castrol customer service.