Which engine oil?

Hey all, just wanted to make sure I put the correct engine oil in my 1600 gti.
Not sure what is in there allready, just needs a top up. Ok to add if I don't know what's in there?
I'm guessing 15w40?
Thanks !

Yes it will be a good choice .

That is the oil for the job, thes old engines love the stuff, no synthetic or semi, nice and thick, plenty of it and change it every 3000 miles

'A Gallon of oil is a good mechanic'

If your not sure whats in then why not change all the oil and the filter rather than topping up  :wink: .