one quart short of engine oil.

[shrike071]

You can mix synthetic with dino oil or mix viscosities with no harm per people on the oil forums. In fact many have their personal "brew" based on professional oil analysis and their experience.

Do what you will. As a retired mechanic, mixing viscosities is not something that I'll ever do, or suggest to anyone else since you'll really have no idea what the final viscosity will end up being. Mixing synth with dino will in essence 'dillute' the synthetic oil - negating some of the synthetic benefits. That is proven fact.