On Alfa number 15
AO Platinum Member
Join Date: Dec 2005
Location: United Kingdom
I agree with Mr-Mac, 10w-40 won't kill a JTS, you might find it burns faster than the 10w-60 However.
10w-60 is about as thick as engine oils get, and there are downsides to using it such as increased drag (more heat and worse fuel consumption), lower oil circulation (more potential for top end wear) and worse protection at high RPM due to cavitation in the bearings.
10w-60 needs to be very hot to work at its ideal operating temperature, you probably wouldn't achieve this in normal road driving in a climate such as the UK. Especially as many TS/JTS engines run with stuck open thermostats.
I would go with the Silkolene 10w-50 as well or a 5w-40 fully synthetic in a TS.
You will never be cool driving a Vauxhall.