[Possm_23]

I read that synthetic oil helps the CI engines run cooler, is that so, and if it does, what brand and who carries it ?

Thanks

possm_23

[ace.cafe]

I don't think it will make the engine run cooler, because the oil has very little to do with cooling in this engine. It is an air cooled engine. It may help to lubricate things a little better, as long as you use the right 20w-50 viscosity range.
It also tends to leak out a lot easier.
Never use synthetic oil on a vintage(Iron Barrel) Bullet that isn't fully broken-in(over 1000 miles on the rings).

If your engine is fully broken-in, it is okay to use synthetic, but don't expect anything special from it. Change it just as often as you would change dino oil. If you get a lot of leaks, then discontinue the synthetic and go back to dino oil.

[Arizoni]

The oils ability to absorb or give off heat is the same with both synthetic or dino oils.

The place the synthetic oil beats the regular petroleum oil is its ability to reach higher operating temperatures without coking (turning to carbon).
This can be a benefit in a air cooled engine where localized hot spots can develop.

Synthetic oil also does not break down as easily as petroleum oils and the makers usually use their best additives in it.
These additives prevent foaming, oxidation, corrosion, scuffing, sludge buildup and thinning due to heat to name a few.

The "Semi-synthetic" oils are basically regular petroleum oil with some percentage (usually minimal) of synthetic oil added.

As with most things, you get what you pay for so I think the small benifit of using a semi-synthetic oil isn't worth the money.

If your RE is a old Iron Barrel or a AVL Lean Burn, meeting the requirements of JASO isn't important in the engine however if you  own one of the UCE models with the transmission and primary drive and clutch that uses the engines oil for their lubrication be sure any oil you put in it meets one of the JASO standards. 

[Blltrdr]

Synthetic = less friction = less heat

[pmanaz1973]

A good friend with a 2012 C5 was running Castrol semi-synthetic for a long while in his bike with no issues.  He decided to "upgrade" his oil to full synthetic Amsoil and started missing shifts.
He went back to the Castrol and his shifts became normal again.

Who knows...magic?

[singhg5]

A good friend with a 2012 C5 was running Castrol semi-synthetic for a long while in his bike with no issues. 

He decided to "upgrade" his oil to full synthetic Amsoil and started missing shifts.

He went back to the Castrol and his shifts became normal again.

Who knows...magic?

After changing oil with a different slipperiness (if there is a word like that, but you get my point ), the clutch/friction plates do not engage the way they used to, because the clutch cable was set to different characteristics of the oil. UCE engines are fed by the same oil that goes to transmission and clutch. 

On changing characteristics of oil, the clutch cable needs adjustment. It may take a very small adjustment - sometimes as little as 1/2 to 1 turn of the clutch cable lock/adjustment nut that will fix the problem.

Full synthetic oil works very well, and so does semi-synthetic - as long as the bike clutch is set properly.

In some cases, synthetic oil leaks out more often than semi-synthetic oil, from very narrow gaps in gasket/covers. Such leaks are very minimal without any serious consequences, if they do occur at all. 

[pmanaz1973]

That was my assessment, but I had no evidence to support it.

I've run the semi-synthetic in my bike and feel it is adequate.  I live in a cool climate and rarely exceed 55mph one-up and no luggage.

[crock]

The synthetic oils using an Ester based stock will cool better than other oils because the dipole characteristic of the ester oil helps with the heat transfer. The effect was significant with air cooled VW's, but I don't know about the significance in a UCE.

[crock]

Motul and Redline use Ester based oil stock.