What would be a good hydraulic oil for a 225 cat excavator? 10w engine oil or 32 hydraulic oil? Also, if the system has 10w engine oil would there be any harm using 32 hydraulic oil as a top up? I know 32 hydraulic is the same viscosity as 10w engine oil.
ISO VG32 hydraulic oil is actually quite a bit lighter than an SAE 10W "engine grade" hydraulic oil. In reality a 10W oil (with a viscosity of around 42 cSt) is actually much closer to an ISO 46 hydraulic oil than a 32. I would say a 10W hydraulic oil for preference, it's what the factory recommends. For top-ups an ISO 46 oil would be the best if you're looking to mix 2 grades of oil for any reason. Make sure that both oils either have zinc as an additive, or are zinc-free, one or the other it doesn't really matter. You don't want to go mixing a zinc-free oil with a non zinc-free oil though.