Yes, I guess 'semi-synth' can have lots of meanings! However, I still don't understand the reference to 'already worn' engines not benefiting from synth oil - unless you mean that the car just isn't worth the extra expense since it'll soon be completely knackered?!
There is NO doubt that the single most significant benefit you can make your car is to replace the oil regularly - before it degrades too much. AND that there are vast differences in oil quality out there. Put simply, if you could afford to run your car on, say, Mobil 1, and you didn't subject your car to too many cold starts/short runs, your engine would pretty much go on forever - many, many hundreds of thousands of miles!
I would simply never run a turbo'd engine on pure mineral oil - and I would chose a recognised 'respected' brand for the (semi) synth too. (I include Comma, Motaquip, etc. in that list - as far as I know they are ok.)
Other things to consider (Big Daddy reminds me
) are how to warm up your car, especially on these frosty mornings.I understand the thing to do is: start her up, let her idle for at least 10-15 seconds, and then hit the road! (By 'hit the road', I mean do as BDC says - keep initial revs to below 2k-ish.) DO NOT allow your car to 'warm up' on your drive at idle, as this is the slowest warm-up you can do, with consequently greater wear. Of course, if your car is frosted up you may need to warm it up a bit to keep the screen clear before setting off, but keep this to a min - and best to use 'fast idle' (1.5k-ish) to speed warm up. Get on the road as soon as you can.)
