What oil should I use?

[Big Lee]

Air/oil cooled engines run hotter than water cooled engines.

At high temperatures the long-chain viscosity stabilising molecules of fully synthetic oil are less likely to break down than those of mineral oil.

Use the best fully-synthetic oil you can afford, irrespective of your bike's mileage!

Greg

Well you learn something new every day!
I`d still put the top stuff in my EVO (if I had one) & the normal mineral stuff in my 12GS (one of which I have )

 

[Islander]

Greg is wrong. Once the engine's fully run in, then fine. Put the expensive stuff in too early and the pistons won't bed in properly.

 

[Greg Masters]

Greg is wrong.

No he's not!

Fact: Fully-synthetic oils offer the ability to remain stable at high temperatures (under which conventional oils begin to breakdown) and remain fluid at low temperatures (under which conventional oils begin to thicken). This provides optimum lubrication at extreme temperatures, reducing wear for a cleaner, more efficient engine. Source

There is no researched evidence that I have found from any reliable source that shows that using fully or semi-synthetic oil at an early stage of an engine's life will prevent bedding in. Indeed many engine manufacturers now install fully synthetic oil from new.

Conversely, there is plenty of evidence to show that oil-failure as a result of overheating or over-use (ie not changing the oil early enough) will result in engine wear (as distinct from 'bedding-in').

The use of low-tech oils like GTX is fine, provided that you use the correct viscosity rating and that they are changed before the molecular chains (which give the multi-grade rating) break down due to heat or age. The wider the viscosity range of the multi-grade you are using, the earlier this is likely to occur.

You guys can shove whatever oil you like into your bikes. From 12k miles I've used fully-synth. I wish that I had done so earlier!

Greg

 

[Deleted account 211025001]

There is no researched evidence that I have found from any reliable source that shows that using fully or semi-synthetic oil at an early stage of an engine's life will prevent bedding in. Indeed many engine manufacturers now install fully synthetic oil from new.

BMW don't!

Or at least they did when the 1200 was first released but then changed to Mineral oil - source Pidcock Motorcycles.

You are perfectly right when you talk about molecular strength / stability being better with synth oils but that is not the only issue.

My experiance has been with racing and tuning Rotax lumps that run similar engine technology to Boxers, ie a lot of roller bearings and very few plain / needle bearings.
Also, like a Boxer the rev ceilings and internal tolerances are nowhere near as high as on a 4 cylinder race rep where you may need a higher shear strength etc.

Despite a number of manufacturers that use the Roatx lumps claiming that fully synth oils should be used (deals with oil companies anybody?) Rotax advocate mineral oils only.

I have seen first hand the damage a synth oil will cause to an engine like this. The oil is just too good/slippery and can allow ball races to slip rather than rotate causing premature and catastrophic engine failure.

Now I'm not saying by any stretch of the imagination that a synth oil will cause that to happen to your Boxer just that there are more issues involved than the usual 'mantra' receited re. the superiour performance of synth oils.

FWIW I intend always using a good quality mineral oil and just make sure it's reguarly changed. I see nothing to be gained by using a synth oil, not mechanically and certainly not financially.

BTW I'm well aware of what a contentious issue types of oil can be so am not trying to pick an argument, just putting forward a point of view bassed on my own personal experiance

Andres