Hi i was wondering if i used a 10W40 semi synthetic oil if it would be thick enough. The motor is in good condition and not burning and using any oil maybe 100ml every few thousand kms or so.

I dont usually drive on long trips and alot of my driving is less than 20km to get to work and back so my goal is to get bit better economy, on the freeway im only using around 9 litres per 100 km but to get to work and backl and moderate driving conditions its using about 15litres.

10w 40 will be fine.

when choosing oil be more concerned with thinning out when too hot as opposed to being to thin when cold. THere is a very good read about oil floating around on the interwebs that explains it well but the jist of it is, buy as thin a oil as you can easily afford that is deisnged to work in the hottest and coldest ambient tempretures your climate experiences. SO most of the east coast of Oz a 10w40 is great al year round.

Should be fine, as long as the engine is in reasonable condition. I used to put the most expensive oils in my car, but dumping $60 oil every 5,000 km/12 months in 3 cars got to me, so I now run Castrol GTX (20W-50) for 5,000 Km. I wait for specials to come out and buy in bulk, currently $14 for 5 L container, max of 3 per customer, from Supercheap. I figure frequent oil changes are better for a car than expensive oil kept in too long. Of course, if you run a taxi 100,000 a year and changing the oil every 3 months a good synthetic is the way to go.

Cars going well with the new oil engine runs a little warmer but coolant temp is the same, bit better economy averaged out mostly because i do short trips less than 15 km each way.
it doesnt seem to smoke so it cant be to thin and the motor must be in decent condition as ive had a worn tp and if i ran anything less than 20 W 50 it would blow smoke.

I use 10w30 synthetic in my race engine. turn 6700 rpm. I was using 20w50 and kept having bearing failure on #2 connecting rod.

10w40 is fine it what the mitsu dealer here uses

I use 10w30 synthetic in my race engine. turn 6700 rpm. I was using 20w50 and kept having bearing failure on #2 connecting rod.

Race engine is a liiiiiiiiiiiiiitle bit different to a bog stock asstron in this case though.
I'd stick to a minimum of 15w-40

I ran a 5w-30 in the TR (different engine yes yes yes I know) and saw a warm idle oil pressure of under 10psi. Not good. with a 15w-60 in it now see's a warm base idle of almost 40psi.

I know it's different but over here the 2.6 engines call for 10w30 summer and 5w30 in winter. I had all sorts of problems using 20w50 (can't prove that was the cause of my problems) but when I switched to 10w30 full synthetic, my problems all went away. I have 70psi oil pressure hot @1500 rpm.