Hi guys.
I would just like to get your opinions on the following.
In the service manual of our datsuns they state that engine oil of weight 30W or 40W must be used and with the API specification of SF.
On my previous thread I posted on engine oil some guys replied by saying they use synthetic oils.
I am using Castrol GTX2 with the specs of 20W-50 and SL as the API.
Is it possible that we are using too advanced oil for the engine in the way that it will cause more harm than protection? I read once in a cars service manual "do not use synthetic oil".(cannot remember what car)
This is just out of curiosity what I want to know what you guys think.

My personal opinion is that I think we will get longer engine life with todays oils as when we use oils with the specs they give in the manuals.
Meaning the engines was build to use the lower spec oils of those long gone years but we are using far more advanced oils increasing the overal engine protection.

I reckon with the technology that goes into synthetic oils nowadays means cleaner oil that is more efficient in lubricating any motors, not specific ones. I doubt synthetic oils would have a drawback on older type motrs as they would be lubricating them better, which would of course mean greater longevity.

But im no expert ask the other guys im sure theyll know!

You certainly won't do any harm with a synthetic oil, but if the older Datto motors have wider tolerances, you might start consuming the stuff as it blows by the rings and so on.
Operating temperature is also an issue: a 40-weight might be good for an Australian summer, but thinner oil would perhaps be better in very cold conditions.
Also, there's not much point in using a thin, synthetic oil on a motor with a lot of wear: you need a film of oil to damp down movement.

Heinz brings up some interesting points. Among two stroke bike tuners there has been debate on the value of synthetic oil becasue the synthetic can be mixed at 100-1 where as traditional pre-mix is around 24-1. The syntehtic stalwarts say less oil in the mix means more burnable fuel hence ,more power. The traditionalists say the 24-1 has more oil on the cylinder bore therefore offers a better ring seal I.E. hgiher compression hence more power.
So... if your motor is run farely loose I would think you'd steer away from synthetic. I have run motul in the 1200 and due to leaky umbrella seals it puffed a little smoke. Now since I'm racing the car it is no biggie but for street use at $7 a quart Motul could get exspensive. I would use good Ol Castrol 20W-50. Remember I'm in the desert.

Tom Grossmann, Las Vegas

i use penrite semi synthetic and it hasn't steered me wrong yet but don't ask me the weight i use cos i forgot just now i'm drawing a blank

the manual that said to not use synthetic oil probably only meant under the first 1000 miles, on newer engines the idea is to break them in. On my parents pathfinder (with a VG30 engine) its said the exact thing so if u ask me with older motors stick with normal oil if possible and newer models can take both

I prefer to stick close to what the manufacturer says, or at least close on top side, If you run to too higher perfomance than what is recommended, the engine is just going to burn it. the most important thing is to change your oil regularly, otherwise it doesnt matter what oil you run, if it can't clean, it can't protect