One issue that many operators seem to uncertain about is whether all makes of oil are essentially the same as one another and do they offer the same level of performance?

Essentially the answer is no they are not all the same, but perhaps we can clear up some of the differences and point out the issues to be aware of.

The most critical point is to ensure that you use an oil which is approved to the specifications stipulated by your engine manufacturer. We are aware that some of the oils on the market - often at the cheaper end - do not hold approval, and it is the word approved that is key.

It can be difficult to spot an oil that is not approved as the manufacturers can mislead buyers and engineers alike by naming the specifications on the packaging and use rather loose phrasing such as 'can be shown to conform to the requirements of MIL-L-22851'. Operators should be aware that this does not mean that the oil is approved - and therefore subject to the same stringent controls of the specifications - and it will not appear on the specification's Qualified Product Lists.

These unapproved oils have not undergone the rigorous testing carried out by the UK and US authorities necessary to gain approval, and furthermore if an oil does not have approval the manufacturer can change the constituents and formulation of the oil without any independent control.

"So what?" you might ask.

The problems occur when you refer to your engine manual and it advises the use of oils approved to specification X. If the oil you subsequently use is not approved to that specification (or the specification which has superseded it), then you are likely to invalidate any warranty and give an easy let out to an engine manufacturer if you experience mechanical problems.

The specifications pertaining to your engine will be listed in the engine manual, but the common ones are:

All the AeroShell range of piston engine oils are fully approved to the appropriate specifications above.

It is worth pointing out at this point that a different manufacturer's oil can be used to top up the tank if an operator finds himself needing oil away from home. This may compromise the benefits of the additives used in the AeroShell grade, but the oils will be miscible and it will be preferable to running with low oil levels. If you are running in however, you must ensure that you top up with a straight oil not an Ashless Dispersant oil.

One other difference between oil manufacturers is that some manufacture and control their own base oils (referred to as being integrated manufacturers), whereas others buy their base stocks on the open market. It may surprise you to learn that even some of the major suppliers in the market are not integrated manufacturers and buy their base oils from third parties. As you will appreciate, an integrated manufacturer has a greater control over the supply and quality of the base stocks, thus giving a more consistent finished product.

Shell is an integrated manufacturer, producing and controlling the base stocks for all its AeroShell range of piston engine oils.