Oil Advice For 1990s Era Yamaha ATVs

[DockHoliday]

I have taken ownership a fleet of circa 1990 Yamaha quad bikes with air cooled 350cc single lung motors. Bikes had been sitting in a garage unused for 15+ years. Usage prior is unknown, as is the maintenance history. I had a local shop clean the carbs, adjust valves, replace all fluids, lube all things that take lube, replace all wear items, etc. All are running well now. Shop used no-name 10W40 Dino oil.

Machines will be used in all seasons in WI, so they will see a variety of temps (winters here can get down to -25F).

My question is should I consider switching to a synthetic oil? If so, what vis and flavor? So many people say no to switching to synthetic on older engines, but I thinking this is an old wives tale.

Thanks in advance.

 

[14Accent]

Even being air cooled, wouldn't 10w-40 be a bit thick at -25? I'm thinking a 0w-40 below, say, 10 degrees and a 5w-40 up to about 60 degrees. After that, a 10w-40 should be fine. Synthetic shouldn't hurt it at all, if anything it will give you that little bit of extra protection.

 

[Vern_in_IL]

any JASCO rated oil would work, I prefer synthetic for anti shearing.

 

[kschachn]

Originally Posted by Vern_in_IL
any JASCO rated oil would work, I prefer synthetic for anti shearing.

Synthetic would be more shear resistant if it uses less VII, but neither synthetic nor conventional base oil will shear.

 

[DockHoliday]

Any concerns with synthetic causing oil leaks after decades of Dino oil? Or is that an old wives tale?

 

[BusyLittleShop]

Understanding synthetics means more refining to remove less desirable
elements from crude until what's left is mostly higher-performing
molecular structures. Waxy stuff had to go because it made oil congeal
at winter temperatures. Aromatics had to go because they lost
viscosity too rapidly when hot. Unsaturates had to go because they
were vulnerable to heat-driven gumming and sludging. And so on.


What you are paying extra for are uniform sized molecules that don't
exists naturally in abundance...

Yamaha offers a 0w40 synthetic...

 

[krismoriah72]

Originally Posted by DockHoliday
Any concerns with synthetic causing oil leaks after decades of Dino oil? Or is that an old wives tale?


Nah not really. What you have to watch for on used ATVs are consumption rather than leaks. Dirt gets past the air filters and 'dusts' the engines causing ring wear which leads to consumption.

So with that being said I would run the universal favorite Rotella 5w40 and keep an eye on the oil level every few hours of usage.. to weed out the oil burners.

"Diesel oil has the widest performance range with 5W40," says Mark Betner of Citgo. "Its starting temperature range is down to minus 22 F (compared with 15-plus with 15W40) up to 122 degrees F (same as 15W40). That tells you a couple things: There's a 37-degree cold cranking advantage (from minus 22 to plus 15) to a 5W40 and the same benefit on the high end."

https://www.overdriveonline.com/through-thick-and-thin/

 

[sunruh]

where is the P66 TropArtic ?

speaking of old school

 

[DGXR]

Yes it's an old wives' tale. The idea was, conventional oil is not as good at keeping engines clean as is synthetic oil. So if you have an engine that's been running conventional for a long time, then start using a synthetic, it might clean out some bits of buildup/sludge that were keeping a leak at bay. In other words, synthetic could potentially reveal a problem that was already present. This has not proven to be the case.
The truth is that synthetic as significantly better flow than conventional and will find its way through tiny cracks and other spaces where the conventional would not wander, causing seepage. But not leaks.

I agree with the 0w40 recommendation, considering your anticipated ambient temperatures.