'83-'88 fuel consumption?

Hi, i'm looking into buying an older model 3 series BMW and was wondering what the fuel consumption was like in them. In particular the 83-88 318i against the same year model 323i or any model with the 2.3 -2.7 litre 6 cylinder engine. I have looked around for their technical specifications on the net but can't seem to find anything. I just need to know on average, how many litres/100km each model would get in different types of driving (city/highway/average). Also how great would the difference between an manual and auto be in fuel consumption.

Thanks guys, and if there is anything else you think I should be looking out for in these cars feel free to voice it. :)

P.S Fuel consumption allowing for 20+ year old average engine.