15W40 vs 20W50

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Mar 26, 2022
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I ride a Kawasaki 1700 that I bought new. The book specs 10W40, but I have been using 15W40 T6 in it since the second oil change. I have been reading around and found that a lot of people have been using 20W50 motorcycle oil in the 1700. Since T6 (and T4) are hard to find this year, I have been thinking about switching to 20W50. Am I going to screw anything up by making the switch? Am I going to gain anything?
 
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May 12, 2017
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I ride a Kawasaki 1700 that I bought new. The book specs 10W40, but I have been using 15W40 T6 in it since the second oil change. I have been reading around and found that a lot of people have been using 20W50 motorcycle oil in the 1700. Since T6 (and T4) are hard to find this year, I have been thinking about switching to 20W50. Am I going to screw anything up by making the switch? Am I going to gain anything?
I switched my C90 to Mobil1 15w-50 and have no complaints.
 
Joined
Dec 9, 2011
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Ca USA
Blackstone's 35 years worth of racing and street motorcycle oil
analysis shows no significant differences in WEAR between the
grades... in other words either a 30 grade or a 40 grade will meet
and exceed your mileage expectations... but due to unwanted oil drag
what you loose between the slow moving 40 and quick moving 30 is
less HP and higher temps...


full-45634-35309-oiltubeviscositytest.jpg
 
Joined
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I ride a Kawasaki 1700 that I bought new. The book specs 10W40, but I have been using 15W40 T6 in it since the second oil change. I have been reading around and found that a lot of people have been using 20W50 motorcycle oil in the 1700. Since T6 (and T4) are hard to find this year, I have been thinking about switching to 20W50. Am I going to screw anything up by making the switch? Am I going to gain anything?
You do not mention the climate you ride in or what area of the country.
I routinely ran 15/40 winter oil and 20/50 summer in my metric 1300 Yamaha. My area summertime temperatures are always above 90 degree highs and shifting always used to suffer with less than a 50.

I wouldnt run 20/50 below 50 degrees though and if my local climate was only in the 70s to low 80s with no heavy traffic conditions I would stay with the 15/40 or as long as your shifting stays ok.
 
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Decatur AL USA
Blackstone's 35 years worth of racing and street motorcycle oil
analysis shows no significant differences in WEAR between the
grades...

Let your Harley idle in traffic with the low oil pressure light on with 40 Grade or run 30 grade on track days with 300F oil temps in your oil cooled GSXR? I suspect things are slightly more complicated than the raw numbers suggest. While you will see some slight changes in oil temps with change of grade the grade still needs to match the peak temp.
 
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pa
as noted your climate is a factor in oil choices, as is how you ride + the wear on your engine as looser clearances suit heavier oil. water cooled i assume BUT still prolly harder on oil especially if its shared with the tranny!
 

dnewton3

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Indianapolis, IN
What‘s wrong with using the recommended spec JASO MA 10w40?
Nothing "wrong" with that, but it's more difficult to find and more expensive than T4, which I find puzzling that the OP states it's "hard to find".

T4 has been on the shelf at WM, RK and other parts stores without fail in my area. 10w40 MA is pretty much a motor-sports specific lube, where 15w-40 has a MUCH wider market base due to diesel applications, obviously. In my area, it's just the opposite; 10w-40 MA is nearly non-existent except at motor-sports retailers, and it's very expensive. T4 is everywhere and about $14 a gallon; half of what 10w-40 costs.
 
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Let your Harley idle in traffic with the low oil pressure light on with 40 Grade or run 30 grade on track days with 300F oil temps in your oil cooled GSXR?
Quote BITOG DrDave
My old Harley really liked 10w-30 Amsoil. These was a significant
reduction in wear metals going from 15-40 to 10-30. There were no
consumption issues. It certainly started easier. By easier I mean it
spun over much faster. The motor seemed quieter, and Harley's need all
the help they can get in that department.
 
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2017 Kawi Voyager 1700. Bought new. I run 4 qts Motul 7100 10w40 and 1 qt Motul 7100 20w50. That seems to be the best all around I could come up with. If I ran 5 qts 20w50, but just seemed a bit sluggish. Bike rides in Ohio.
 
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UK
normally the owener's hanbook give a couple of option depending on outside temperature range.
I would be comfortable with going to 15w in a mild to warm environment or even 20W in very warm to hot environment.
But would stay with 10W in 15deg C and lower evironment.
 
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You only need 20w50 if you live where the ambient temperature goes above 104f regularly.
Widely available T4 15w40 is good up to ambient temperature of 104f.
 
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South Carolina
I know lots of Harley guys that use 15W-40 Diesel oil in the sump. Typically it was okay.

I do remember we had done a VFW parade for Memorial day in Georgia. It was pretty hot out. Lots of slow speeds, idling, parade type stuff. One guy had his oil light kept blinking on him. He had 15W-40 in sump. Fast forward to July, even hotter, and we did the same thing for a funeral. He had since changed the oil to NAPA 15W-50 (car oil.) No oil light flickering. So seems Harleys, with an EVO anyway, like 50WT in the heat. Plus, the Diesel was a conventional oil and the NAPA was a Full Synthetic. Seems to keep cooler on an air cooled engine.

That convinced me though. You could get the NAPA 15W-50 for .99/quart on sale back then. Bought a lot of it.
 
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Jul 12, 2012
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Caldwell Idaho
Blackstone's 35 years worth of racing and street motorcycle oil
analysis shows no significant differences in WEAR between the
grades... in other words either a 30 grade or a 40 grade will meet
and exceed your mileage expectations... but due to unwanted oil drag
what you loose between the slow moving 40 and quick moving 30 is
less HP and higher temps...


full-45634-35309-oiltubeviscositytest.jpg
What temps were the oils in this test?
 
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