How many miles is too many?

[Pavlo]

On an old engine 5-30 might kill it, as it is thinner, it might leak out of the seals. The greater the milage, the heavier the oil you should use (generally). On 177k miles I would go with 10w-40, if it burns it too much, then switch to something a bit heavier. The numbers are just oil weight, the higher the numbers the thiker the oil, therefore making it harder to go past seals and piston rings.