10w/40
40 weight
15/40
No, use only the weight oil as recommended by the manufacture.
It is the weight of the multi-vicosity oil. The 10 is the weight of the oil when cold. The W stands for Winter. The 40 is the weight of the oil when it gets hot.
about 20psi at idle (warm) and 40 to 50psi at 2000rpm.
Running at operating temperature around 40 psi.
5 and 15 is the weight of oil in cold status while the 30 and 40 is the weight of the oil in operating status.
A full operating temperature it will be around 40 psi.
Newer engines are machined to tighter specifications than older motors. Newer motors require a lighter grade oil for lubrication like a 5 or 10 weight. The 5 or 10 weight can move through the engine and get to the places that need lubrication better than a heavier grade of oil. A 10-40 grade moves through the engine like a 10 weight oil with the ptotection of a 40 weight oil. If you put a 30 weight oil in your engine, it will not move through your engine as easily and when it does get to the parts that need lubrication, it does not do as good of a job.
The W stands for Winter. 15w40 is flows as 15 weight oil in the cold temperatures and 40 weight oil when it gets to full operating temperature.
If you use the same weight as The original oil, for example now the engine uses 15W-40, and you do an oil change, filling it with the same specs 15W-40 oil that's no problem for the engine.