Just got a 1982 GS650G have ?

[volsrock1963]

I just got this one owner with 17k miles valves were adjusted at 16k has upgraded Ricks stator and regulator

The owner stated it has always had conv oil in it...would it be OK to go to full syn or semi syn?

[Rich82GS750TZ]

Many of us use Rotella T4 15w-40, because it’s cheap and plentiful, but also because it’s JASO MA, MA2 compliant: means it’s good for use with a wet clutch. It’s semi synthetic.

I have read on here of some who have tried full synthetics and had leaks. IDK.

Just remember, you started this oil thread. Prepare for the sh!tstorm of replies.

[Burque73]

Use whatever you like and is suitable for a wet clutch, with the ratings Rich just mentioned.
If they're ridden somewhat regularly the synthetic stuff hasn't caused leaks in mine. YMMV.

[Nessism]

Synthetic oils are fine. They will remove more sludge than conventional oil, and if said sludge is plugging a leak path, synthetic may uncover that vulnerability.

Lots of people use Rotella, because it's MA rated, but in truth, pretty much any diesel oil is fine. Most diesel oil sellers don't want to bother to do MA testing, so they don't, whereas Shell did. And BTW, Rotella is NOT MA/MA2 certified, they just claim it meets the spec.

Another good option is Mobile 1 15W-50. It's great for air cooled bikes, and has more antifriction additives (Zinc and Phosphorus) than Rotella. And then there is oil like SuperTech from Walmart. They make a good motorcycle oil, both conventional and synthetic. Both with excellent reputation. Honestly, it's hard to pick a bad oil these days. Just as long as the oil is 10W-40 or thicker, you don't need to worry about it hurting your clutch. It's the thin "energy conserving" oils that have the anti friction stuff that can damage clutch plates.

[KiwiAlfa156]

Diesel oils will work. Some folks like them because they have higher ZDDP additive levels. ZDDP forms a localised physical anti scuff coating stopping metal to metal contact in extreme low lubricant , high-pressure, high-temperature contact points. So high ZDDP is desirable in air-cooled engines. The only problem is that diesel motor oil also has very high detergent levels in diesel oil to deal with diesel soot, and this inhibits the action of ZDDP.

https://www.hotrod.com/how-to/diesel-oil-in-gasoline-engine

You might want to watch the Oil Geek and make up your mind on using diesel.

https://youtu.be/HcJHJL5Ys-Y?si=igUbf96vjHZsJhHH

Also most oils marketed as 'synthetic' (GRP III) are made FROM mineral oil. The refinery breaks up the inconsistent molecules in the dino oil soup (which contains 1000s of different length/shape molecules some good as motor oil, some bad) into smaller bits which they click back together like Lego into the lengths/shapes that actually work well as a motor oil. Think of this type of synthetic as 'ultra-refined' mineral oil.

PAO/Ester (GRP IV/V) are synthesized. Developed in WW2 for air cooled aero-engines and jets, all the molecules are identical. They are 'shear stable' stay in (viscosity) grade. Offering the same film strength when you change it out as when you poured it in. Even after going duty in the gearbox, where mineral quickly gets sheared to bits (especially the VI improvers) and rapidly loses viscosity. Which is why you have to change mineral after short intervals.

And remember mineral/synthetic refers to the base stocks. The add-pack, which can be up 10-30% of the oil by volume in the jug, is what tunes the oil for its intended application. That is, friction-modifiers to improve mileage (but can negatively effect wet clutches), anti-wear, anti-foam, seal swelling agents, detergents for cleaning, anti-sludging dispersents that suspend particles, etc.

Old bikes can benefit from new technology. I bet the tires on your bike aren't the same tech that it rolled out of the showroom on.

[Grimly]

Even after going duty in the gearbox, where mineral quickly gets sheared to bits (especially the VI improvers) and rapidly loses viscosity. Which is why you have to change mineral after short intervals.
.

No matter what synthetic I've used, the gearbox kills them all at 2000 miles.