A serious question about synthetic oils

[Soliton]

First up. I am not interested in a flame war.

My question is why do we not use synthetic oil in out bikes? Something like 0w40 fully synthetic Mobil 1 (Yes I gave a brand name.)

Answers from my mechanic and others.

It's too good for them.
I want to use the very best oil I can to minimise engine damage related to poor lubrication.

It will burn oil.
I don't care, 50ml of oil here and there is cheap insurance if it protects my engine better in the long run. And that's about all it has been so far.

They are too thin.
The aim of standard viscosity is to ensure...standard viscosity. At 100 degrees any 40w oil, mineral or synthetic, has a viscosity of approximately 16 centiStokes. Further when it is cold a 10 weight oil has a viscosity that is so high that it provides very poor lubrication at start up. It would seem incredibly advantageous to engine life to use something like 0w40 that almost usable as soon as the engine is cranking over and not 90 seconds later

It will make your seals leak.
I have been using 10w40 synthetic as an experiment since my last oil change and it has never any more than mineral oil. I have always had a tiny bit of seep but never enough to put a drop on the carpet under my bike. My bike has 85,000km on the clock so its no spring chicken. My own experience (and it is only mine) says the leaky seals thing is BS.

BMW don't recommend it.
11 years ago these kinds of oil weren't available. The company is not going to recommend something that didn't exist. My bike is also long out of warranty.

The viscosity modifiers could ruin the clutch.
Dry plate? Please grab me by the throat if I am missing something on this one.

So far my experience has only been positive with the 10w40. The initial startup chatter, fairly mild anyhow, goes very quickly now. So I am wondering.. in a climate that gets down to -9 degrees Celcius why not use something like 0w40 fully synthetic. It's much lower viscosity at cold temperatures means that it is protecting my engine far more quickly than something than a 10w40 oil.

I'm not tying to be a smart$ss. This is a serious question. I have read everything I could lay my hands on at the "bob is the oil guy" site and there doesn't seem to be any reliable reasons, and worse still I have heard some utter rubbish. One person told me that synthetic oil has additives that make it thicker when it gets hot.

I am trying to work out if we don't do use them for a good reason, or it is just a series of "justifications" My mechanic charges me the same rate for 3 litres of mineral oil as I pay for 5 litres of fully synthetic, and i would prefer to use the very best product I can if it is safe and reliable.

So...

What's the story guys?

And to re-iterate. I am not trying to stir the pot. I'm looking for a solid science/engineering based answer that has a bit of proof/reliable testing behind it.

Sol

[Clem]

I'm NOT an oil expert, just a rider who used Mobil-1 (Oops, said it again!) 15W50 exclusively with BMW oil filters in my '96 R1100R for 15 + years with no leaks, no bad seals, or excess usage. It ran great, and I intend to use synthetic in my 2012 Roadster after it's fully broken in.
FWIW, STILL using it (didn't say it!) in my 2004 R1150R with no ill effects. I like to change the oil myself. 5-qts. of synthetic oil at Wally World
is less than the dealer wants for his dino oil. YMMV

[sjbmw]

A few years ago I was asked if I wanted synthetic fluids for my spring annual service.
Up till then (the first 29k miles) it was purely fossil fluids.

I said yes, and when I picked up the bike and rode off it it, I could literally feel how smooth it ran.
Engine, Shifting, etc it just felt smoother. Surely a valve adjustment mattered, but months later the smoothness was still there.

Even my kid who had been riding pillion for several years on the R told me on the way to a rally that he noticed less vibration when on the back of the bike.

I can't back any of this up with science though.

[Ton1959]

I use synthetic oil the 15W50 from Motorex. Motorex boxer was made for our bikes. My bike is hardly using any oil since I have started using it.

[grwrockster]

Just to be confusing - I'm in the other (non-synthetic) camp.

It's too good for them.
I want to use the very best oil I can to minimise engine damage related to poor lubrication.

It will burn oil.
I don't care, 50ml of oil here and there is cheap insurance if it protects my engine better in the long run. And that's about all it has been so far.

Why not? I used to work for Castrol Distributor years ago and their Technical Engineering Dealer Support advice was nearly always the same mantra - "use the specification, grade and type of oil recommended by the manufacturer".

On the first point - remember the engine was designed to work with the oil around 11 years ago. So the modern synthetics can be 'too good' for your engine as suggested by your second point. But why might the engine burn oil with synthetic oil used? Because the oil is so good that the oil scraper rings can't do their job properly. This then leads (in bad cases) to be bores becoming polished (bore glazing), which then leads to piston blow-by, loss of compression, crankcase pressurisation and increased oil consumption (the increased crankcase pressure can also lead to more oil seal leaks). The oil increases the carbon deposits on the valves and combustion chambers, leading to poor valve seating and more compression loss.

If your engine isn't well-bedded in, then too good an oil can prevent it bedding in.

Some engines are affected more than others (I've seen diesel engine models in my workplace that have suffered badly from bore-glazing, while others are far less susceptible). I can't comment on what the BMW's behave like on synthetic myself, as I don't use it (But as they are known to need maybe 20k plus miles to bed in and stop using oil, its a good bet that putting synth oil in would slow or halt that process). I stick to the advice the Tech guys at Castrol gave me years ago, and stick to the the stuff BMW put in the book.

[gregor]

After I switched to ,thicker, semi synthetic 20W/50 the cam chain noise was considerably quieter. So thinner oil may cause problems there.

[Ol' Jeffers]

I'm with grwrockster on this! Even Yamaha recommend NOT using any synthetic oils until the engine has bedded in
on their big twins.
However I was using Mobil 1 in my Norton 750SS Atlas back in 1976! Yes, synthetics have been with us for a while!
As my Norton used to burn oil irrespective of the type of oil used it seemed wise to use an oil that
would at least give good protection while it was actually in the engine!
My BMW guy uses what BMW recommend. I ain't gonna argue with him!

[swamper]

I use 20/50 motorcycle Valvoline and haven't lost an engine yet.