Thanks Laird,
my Volvo Service manual said 10/30 or 20/20, while Haynes just say Castrol GTX, but it was probably the driver's handbook that said 20/50 (I'd have to re-check), and Brooklands list Valvoline 20/50 for the 164. I'd be inclined to think the Volvo Service manual knows best, but it is an old publication and things have moved on.
I use 20/50 in my 61 Morrie but that's a simpler and older engine, and most people seem to think that's Ok for it.
It sounds from my quick googling in response to your suggestions that 20/50 might be a bit thick at operating temperature in an engine in good condition, which I fondly hope mine is. It would probably be better for a more worn engine?
And that the 20 bit is also a bit thick and will slow flow when cold starting?
So I think I'll take your advice and try for 10/40 or 15/40.
With the ATF; my Volvo Service manual says type A for steering and type F for trannie. I have no idea how or even if they differ but I'll check.
Thanks again,
Leroy
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