10w30 is a thick oil, while 5w30 is a thin oil in viscosity. 5w30 is used in cold temperate regions because the engine must start in cold weather. On the other hand, 10w30 is a thick oil that performs better in engines used in hot conditions. If you start using the 10w30 thick oil in vehicles that hold the capacity of bearing thin oils, then oil will not flow properly in such vehicles. It can lead to wear and tear of the engine as oil will not lubricate and can damage the engine.