The Factory Service Manual is available from a number of links in the tech section. Page MA8 shows recommended viscosity for a range of operating conditions based on anticipated outside temperature until next oil change. A 10w30 or 10w40 is advised for temperatures between -18* and +38*. Given the age of these engine I would go for the 10w40. Nulon make a fully synthetic 10w40 http://www.nulon.com.au/products/Engine_Oils/Full_Synthetic_10W-40_Hi-Tech_Fast_Flowing_Engine_Oil/ that is reasonably priced.
so is a 15 40 not ideal? i'm running 15 40 at the moment. but i have just been told this hx5 is a premium mineral. being 24 years old, it wouldnt be a bad thing to run a mineral would it?
Re weight I don't honestly think it's going to make a huge difference, I'm just thought the manual was a good starting pony when selecting a suitable oil for the car. I realise I'm probably in the minority in that regard... The age of the car has no bearing on your choice synthetic v mineral oil. They will both do the same job, the synthetic will simply do it for longer before it stars to degrade.
15w40 is perfectly fine. The aus spec engine bay sticker actually says you can run up to a 20w50 as long as ambient temps are above 10deg.
True. when I was working at Autocheap, I often had guys coming in getting basic mineral oils for late model commodores and falcons that are on 300,000k's with the original engine. they often said they have always run with mineral. I might just go with the hx5 then. seems like it should be ok.
why not go the hx7.. supercheap have it for sale ATM for 16.99 each bottle. im going to get a few bottles..