Hi Toby/Garry,
Yes.. it is the particular properties of the oil required that govern which type is required. It's much the same as buying oil for your car in that years ago, a 20/40 would do the job for all-year-round performance.. depending on the car of course. Old, vintage cars tend to need a much thicker oil (forget the 40 bit!!) so
any similar 20 grade would do the job. With any new car, you are given alternatives for the type (and grade) of 'approved' oil that can be used and aircraft are no different in this respect.
The Vickers documentation specifies (for the Vanguard)..
Castrol 98
Aeroshell Turbine oil 750
Esso Aviation Turbo Oil 35
Esso Turbo Oil 35
Enco Turbo Oil 35
Esso Extra Turbo Oil 274
Enco Turbo Oil 274
Texaco Synthetic Aircraft Turbine Oil 35.
There are a list of temperatures certified by Rolls Royce that some (though not all) of the above oils can be used at and other temperatures that the rest can be used at.
Of course, it is never particularly good practise to 'mix' different oils, even of the same specification so keeping to what has been used before is best for the job.. unless sufficient (cheap) quantities of a 'different' oil can be found to enable a full oil change
ATB
DaveB :tab: