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Let's talk oil viscosity

Posted: Fri Jul 10, 2015 9:27 pm
by radare
Here's the recommended oil viscosity for your XJ600 & Seca II:

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Yamaha recommends 10W30 and 20W40 depending on temperature. Unfortunately for us, the 20W40 oil is no longer available. Common viscosities for engine oil are 10W40 and 20W50. I use both in my XJ's. Here's a revised oil viscosity table showing what I think you should use:

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What are your thoughts on this? What do you use, viscosity wise, and when? Any recommended reads on current oil standards?

Re: Let's talk oil viscosity

Posted: Sat Jul 11, 2015 12:51 am
by predrag80
For my first oil exchange I used Repsol 20W50. But my gear exchange was noisy in first gear. Now I am thinking of using 10W40 and, if it's possible, to swich on Silkolene or Liqui Moly, although those are harder to find in these parts.

Re: Let's talk oil viscosity

Posted: Sat Jul 11, 2015 10:01 am
by TonyKZ1
Hmm, you're recommending to use the 20w50 during the summer months? Yea, with the hotter temperatures I can see that as I know mostly all the big V-twin air-cooled engines all run that viscosity. However, I wonder with the higher rpm of our motors (at least higher compared to the afore-mentioned a/c v-twins) would it be any problem using the 20w50. Wonder if or how much it would change/improve the engine/tranny performance or just be an option to make it last longer or handle the heat better? It'd be interesting to hear the other replies to this topic, too.

When it starts cooling down though, I can see switching back to the normal 10w40 or even the 5w40 (Rotella) as that sure made a difference starting in the winter time on my last air cooled bike.

My last oil change on this Seca II, I used a full synthetic 10w40 motorcycle oil (AMSOil). It's about time to change the oil & filter again, but with the oil leak that I've got now (looks like the clutch cover gasket is leaking), I've got to replace that before I change the oil so it doesn't seep/leak/drip out all that expensive oil. My RonAyers.com order just came in yesterday so the gasket and a few other parts are here now.

Re: Let's talk oil viscosity

Posted: Sat Jul 11, 2015 10:24 am
by radare
Let me take a step backward and explain what those numbers mean. There are two types of oil on the market and they are rated based on their viscosity (or resistance to flow) at a temperature.

A straight-weight oil is represented by the notation SAE 50W. This is an oil that does not have viscosity modifiers and is rated at a viscosity of 50W at 100-degrees C (16.3 centistokes (CST) at 100degrees C Kinematic Viscosity). As the number increases, the kinematic viscosity increases. A 20W oil is ligher than a 30W oil and so on and so forth.

A dual-rated oil is represented by the notation SAE 20W50. Like the straight-weight oil, this oil is rated at a viscosity of 50W at 100-degrees. The difference here is that it flows like a 20W oil at cold temperatures (I can't recall the lower temperature used to test). This is achieved by using viscosity modifiers. These are long-chains of polymer that uncoil as they heat up (or vise-versa). When they coil, the fluid viscosity changes. This is good because it allows the oil to flow more freely (less viscous) at cold temperatures like cold-startup and then offer better protection at high temperatures.

Here's a good article on all of that: http://www.upmpg.com/tech_articles/motoroil_viscosity/

Now, that being said, most wear in an engine occurs at startup, when the engine is cold. The oil takes a few moments to flow through the engine and lubricate it, tolerances are looser and things bump into each other causing wear. To me, that indicates that I ought to be looking for an oil with a lower number at low-temperatures, for startup protection.

Our engines run hotter than 100-degrees C. I've seen the cylinder head temperatures on mine climb well over 300F in stop-and-go traffic in July. The 50W gets its viscosity rating at 100C but continues to thin-out the hotter it gets. So to me, I want an oil that has a higher base-weight for those months when I'm going to see triple-digit ambient temperatures.

If the ambient temperature is always above 80F and can climb to 100F or more, I think it makes good sense to run the 20W50 oil for top-end protection while idling.

If the ambient temperature is less than 80F and there isn't risk of triple-digit temperatures, I think the 10W40 oil would be better for the cold-startup protection. And if its below freezing, I'd consider a 0W or 5W oil for startup.

Based on the thought-process that ensued from this post, I'm considering the revised chart:

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Re: Let's talk oil viscosity

Posted: Sat Jul 11, 2015 2:09 pm
by Sirhc
I'm running fully synthetic 5w30 car oil. Lots of short trips for me in UK temps (seldom above 15c :-( ) so start up protection is a big one for me.

LOTS of interesting info (real world, behind the marketing hype type stuff) here on motor oils:

http://www.ducatimonsterforum.org/index ... pic=1912.0

Well worth a read... if you have a few hours!

Re: Let's talk oil viscosity

Posted: Sun Jul 12, 2015 11:39 am
by TonyKZ1
Sirhc wrote:I'm running fully synthetic 5w30 car oil. Lots of short trips for me in UK temps (seldom above 15c :-( ) so start up protection is a big one for me.

LOTS of interesting info (real world, behind the marketing hype type stuff) here on motor oils:

http://www.ducatimonsterforum.org/index ... pic=1912.0

Well worth a read... if you have a few hours!
That's quite an interesting reading on oil. Thanks for posting that.

Re: Let's talk oil viscosity

Posted: Tue Jul 14, 2015 1:06 am
by MichaelX
I had repsol 10w40 full synthetic but i dint like it+ i got clutch slip with it. Now I'm running Motul 5100 10w50 semi synthetic, something i noticed different is it pulls better but it gets hotter.

Re: Let's talk oil viscosity

Posted: Tue Jul 14, 2015 5:31 pm
by Seca Guy
I have been running Castrol 4T 4 stroke Motorcycle 20w/50w Since I bought my SecaII in 2013. Here in So. Cal ( San Fernando Valley ) we get temp in triple digits (110) and as cold as 28 deg. and have had no problems of any kind. It fits these requirements. API SERVICE: Exceeds API SG JASO (T903): JASO MA-2
VISCOSITY: SAE 10W-40 // 20W-50. :twocents: :twocents:

Re: Let's talk oil viscosity

Posted: Mon Sep 18, 2017 7:35 am
by anonymous-j
Resurrecting a long dormant thread... I was surprised to learn that shear breaks down the additives and reduces hi temp viscosity over time... to a 10w40 performs like a 10w30, 20, eventually 10. Yikes and good argument for timely changes!
Info from Radare's link above: http://www.upmpg.com/tech_articles/motoroil_viscosity/