Hi Emre-K. I just thought that by switching to synthetics, I will benefit from their good performance.
The way I see it, the primary advantages of synthetic oils are: (1) longer oil change intervals; and (2) better resistance to shear and break-down.
The benefits of the longer oil change interval are largely negated by the increased cost. In the USA, I can buy a liter of Castrol GTX or Kendall GT-1 for $2.50
. Alternatively, I can buy a liter of Mobil 1 or Castrol Syntec for $7
. Let's forget about the fact that Mobil 1 and Syntec use Group III (hydrocracked petroleum) base stocks and are, therefore, not even "true" full synthetics. If I want to buy a genuine
synthetic oil that uses a Group IV (PAO) or Group V (usually ester) base stock, my cost will be closer to $10
per liter. In other words, my total costs are about the same whether I'm using a synthetic oil (changing it every 10K miles) or a conventional oil (changing it every 3K miles). For me, longer oil change interval is therefore a moot issue.
As for thermal breakdown, this really isn't an issue on such a large capacity engine that spins at such low revs. We're not talking about an S14B25 race engine from an E30 M3 track car that runs at wide-open throttle and bounces off its 8K rev limiter for hours at a time. Our cars are cruisers with big, lazy engines that hardly top 2K rpm in normal street use. Even in the Kalahari, the oil isn't going to be taking so much abuse that you have to seriously worry about break-down.
On my Lancer Evolution VIII (400hp from a 2.0L turbo 4-banger), I would run Motul 300V or Torco SR-5 race lubes, both of which use a dual-ester (Group V) base stock. On my BMW 325is (165hp from a 2.5L SOHC inline-six), I run regular oil...even on the track. Just like everyone else who races older BMWs. And I assure you, running a car on the track is much harder on your motor oil than driving to work!
But from all the info you guys gave me, I am going to stick to a good quality mineral oil like Mobil or Total. I think I will stick to a 25W50.
The M117 seems to work best with a heavy oil. In the summer months, 20W-50. If it's really hot (like 40C), you might even want to add some Lucas HD Oil Stabilizer to thicken the oil even further.
Eirik, You let me think back about my military service in the South African defence force, back in the old days when it was still compulsary to do military service. I was on a 10 day camp at a military base in Kimberley. There I experienced the coldest days of my life!! Not nearly the minus 20 or 30 degrees you have, but it was around minus 7 degrees.... Very cold for someone used to 35 to 40 degrees celcius... I remember struggeling to put ammo into the magazines with my blue fingers....
It's all a matter of what you're used to. I used to think 5C was cold. Then I spent several years in Canada. Now, I don't think it's cold until we're down past -15C or so.