0W40
5W40
10W40
all fine to use, they're all THE SAME VISCOSITY AT 100DEG C
the 0, 5, 10 refers to the viscosity at 0degC, the lower the number, the lower the safe cold temp it can go down to (ie 0W goes down to -25degC IIRC, 5W -15degC, 10W -5degC - figures aren't exact its to convey my point)
so if you say a 0W40 is "too thin" - no, its thinner at 0deg C, but EXACTLY the same at 100degC as a 5W or 10W