engine oil

Quick question what grade of oil should i run in my 1.8 injection gti the haynes states 20/50 i think the garage tell me 10/40 semi the car has done 80k miles

How often were you thinking of changing it? Do you drive your car all the time?

every 3000miles or every year and it will be used all summer  long

So, if its not used through the winter, or for extended mileage, its much less critical. I'd not go above 15W rating though (in other words, 15/40 mineral oil would be fine, but 20W/50 is pushing it a bit).

The point being, the thicker the W bit, the thicker the oil is when the engine is cold which is a double edged sword. On the one hand, it makes cold starting harder; but on the other, it doesn't flow off the metal so quick, so it protects better/for longer, if left without use.

15W/40 mineral oil isn't used much these days so you may well find that 10W/40 semi-synth is easier to find and/or cheaper (indeed, may well be the cheapest oil on the shelf these days!)

if i could get 15/40 semi that would be a good bet then because i can

10w40 is what you want, quantum synta silver or fuchs titan