Generally synthetic turbine oils in one viscosity group are compatible and miscible with all other synthetic oils in the same viscosity group (and in many cases other viscosity groups as well). However, in changing from one synthetic turbine oil to another, an operator must follow the engine manufacturers’ recommendations. Change by top-off (mixing) allows the changeover to take place slowly and there is increasing evidence that this is less of a shock to the engine and engine oil system. While most engine manufacturers allow change by top-off (mixing), other engine manufacturers do not and only allow changeover by either drain and refill, or drain, flush and refill.

It’s Shell’s policy to always recommend that the engine manufacturer’s recommendations are followed. In addition, it’s recommended that for the initial period during and after changeover, the oil filters are inspected more frequently.