Pulsar NS 125

[Johnny25]

Hello BITOG,

I'm from Portugal, and I'm new on the forum.
I am a visitor whenever I get doubts about oil properties.
I've never created an account until now, because as I search the web, I can never seem to get my doubts fade away.

I have a Bajaj Pulsar NS 125.
It's a 125cc single cylinder engine, air cooled.

The manual specifies 20w50 JASO MA.

The dealership where I bought the bike used Motul 7100 10w40.

I used on last autumn/winter maintenance Motul 7100 10w50.
But after 1500km I noticed the oil went dark like I've never seen on this bike (the 10w40 while being used, maintained the red colour).
I suppose the 10w50 was getting the viscosity additives getting burnt.
And probably, 10w50 is too much of a spread in a shared sump.

I know that Bajaj shares a lot with KTM, and KTM uses 10w50 on most bikes. But mine is a solely air cooled engine.

This is a bit of a long post, but my doubt is:

As I live in Portugal, climate varies a bit.
Summer is hot 25/40c
Winters go near 0c ( a bit rare)

I read that one of the things that dictates oil viscosity are bearing clearances on the engine.

So, shall I continue to use the 20w50 that the manual recommends (possibly going to a 15w50), or is the 10w40 safe?
Even for long rides (200km)?

 

[Cujet]

More likely, the oil viscosity requirement is an attempt at maintaining adequate lubrication in a hot air cooled engine. It likely has very little to do with the clearances, which I'll bet are normal for any similar engine.

I like Mobil 1, 15W-50 for air cooled engines. It's a robust oil with a high HTHS (viscosity at high temp) and is quite resistant to shear. Mobil also makes synthetic motorcycle oils that are world-class excellent. The 10W-40 and 20W-50 will both do quite well (seasonally) in your engine.

Of note, Mobil's 10W-40 MX4t and one of Motul's 10W-40 synthetics are "strangely identical" ......

 

[Johnny25]

I read around here that 10w40 transfers heat (cools) better than a 50 weight oil. So I keep getting confused why Bajaj/KTM designed this engine to use a 50 oil.
****, I must be overthinking things! ahah

The thing about M1 15w50 is that is a bit rare to find here in Portugal, and if I find it; prices are a bit steep.

Both Motul 15-50 and 20w50 are the same price (11€ a litre).

 

[Cujet]

So I keep getting confused why Bajaj/KTM designed this engine to use a 50 oil.

I'll bet your questions would be answered with an oil temperature gauge. The oil temp is probably just fine in normal use, but during a full throttle hill climb, I'd guess it climbs into the "danger" territory. Air cooled engines are well known for high oil temperatures under certain conditions.

Short of designing a motorcycle engine that does not shear oil, and that runs at acceptable temperatures all day, every day, the answer seems to be high viscosity oil.

My Cessna 177RG has a 200HP, Lycoming air cooled engine. Here in Florida, it's hot and humid almost all year long. The oil requirement is straight 50 or straight 60! The oil temperatures reach the 240 degree range coming OUT of the oil cooler. Thinner oil would result in rapid engine wear and subsequent failure.

The very same oil requirements exist for many Harley Davidson air cooled motorcycles. 20W-50.

In conclusion, it's probably a very good idea to run a robust oil during hot weather.

 

[ZeeOSix]

I read around here ...

I've seen no technical studies that shows any significant heat transfer difference between oil viscosities. If there is any difference, it's so small that it won't make any real difference in engine temperature. It is true that a thicker oil will make the oil temperature increase some because it heats up more when sheared in the bearings, but that's different than the cooling effect of oil based on viscosity.

 

[Johnny25]

So based on your replies I should keep the 20w50 or a 15w50?

I will be doing a large journey next month, 1800/2000km total,always going on the 70/90kmhr which is 6500/8500rpm, with an occasional redline straights.

I'm a bit skeptical about 10w50, because in a shared sump I'm afraid it will shear quickly due to the heat.

 

[ZeeOSix]

So based on your replies I should keep the 20w50 or a 15w50?

I will be doing a large journey next month, 1800/2000km total,always going on the 70/90kmhr which is 6500/8500rpm, with an occasional redline straights.

I'm a bit skeptical about 10w50, because in a shared sump I'm afraid it will shear quickly due to the heat.

I would run either a 15W-50 or a 20W-50 ... preferably a full synthetic. Stick with "50" on the hot end since it is specified in the owner's manual.

 

[BusyLittleShop]

Greetings Johnny
We say oils are graded on thickness but oils are actually graded on flow... a 40 flows faster with less energy than a 50 which means a 40 will increase horsepower and decrease operating temps with no loss in longevity...

 

[Johnny25]

I would run either a 15W-50 or a 20W-50 ... preferably a full synthetic. Stick with "50" on the hot end since it is specified in the owner's manual.

I've contacted Bajaj directly about my motorcycle owners manual, and about the oil.
They said that 20w50 would be optimal for hot weather, so presume 15w50 would be a best all rounder.

I notice that this bike likes to run hot.

Despite being a small CC motorcycle, and being air cooled, I always go for full synthetic. The difference between semi and full synth is 2,5€, so not worth to save on the blood of the engine.
I always choose Motul 7100.

Greetings Johnny
We say oils are graded on thickness but oils are actually graded on flow... a 40 flows faster with less energy than a 50 which means a 40 will increase horsepower and decrease operating temps with no loss in longevity...

Thank you for the explanation.

With 10w40 I noticed less mechanical drag. The bike seemed to have move available power.

Although, I worried about what sounded like tappet noise. Maybe the oil was thin, but not too thin to cause mechanical damage.

 

[ZeeOSix]

I've contacted Bajaj directly about my motorcycle owners manual, and about the oil.
They said that 20w50 would be optimal for hot weather, so presume 15w50 would be a best all rounder.

I notice that this bike likes to run hot.

... either one should work fine, stay with a "50".

 

[BusyLittleShop]

Thank you for the explanation.

With 10w40 I noticed less mechanical drag. The bike seemed to have move available power.

Although, I worried about what sounded like tappet noise. Maybe the oil was thin, but not too thin to cause mechanical damage.

You're welcome Johnny... either grade will meet and exceed your mileage expectations... odds are you'll move up to a bigger bike way before you have to worry about the engine... might has well enjoy the extra power...

 

[Johnny25]

... either one should work fine, stay with a "50".

Thank you

You're welcome Johnny... either grade will meet and exceed your mileage expectations... odds are you'll move up to a bigger bike way before you have to worry about the engine... might has well enjoy the extra power...

The move to a bigger bike is already planned! Ahah

I promised myself and this little motorcycle (since it's my 1st bike), that I would do the mythical road off my country 740km total.
And after that I intend to keep the bike due to it's sentimental value.

Thank you very much, nonetheless!

 

[benjy]

i too like synthetics, even modern cheeper fake synthetic! the thing is oil specs are given at 40C + 100C above 100C oils continue to thin + conventionals are worse in that respect + real man made group IV + V oils are best. conventional oils thicken even faster than they thin beyond the spec temps!!

 

[Johnny25]

Random question that popped into my head:

Using a higher viscosity oil (15/20w50), might mean more time for the cylinder head to get proper lubrication.
As using a wider viscosity oil(5/10w50), might mean more shear that a shared sump bike will have on the oil.

What is more important?

 

[ZeeOSix]

Using a higher viscosity oil (15/20w50), might mean more time for the cylinder head to get proper lubrication.

What is the coldest start-up temperature are you ever going to do? Motorcycles also use a positive displacement oil pump, so unless you're starting in temperatures below the low temperature shown for the oil in the owner's manual then nothing to worry about.

And how long are you going to run the oil? If you change oil often, the it won't shear much.

 

[Johnny25]

What is the coldest start-up temperature are you ever going to do? Motorcycles also use a positive displacement oil pump, so unless you're starting in temperatures below the low temperature shown for the oil in the owner's manual then nothing to worry about.

And how long are you going to run the oil? If you change oil often, the it won't shear much.

Thank you!

Didn't knew that MC's used positive displacement pump.

The coldest starting temperature I ever faced was 2c, and I don't plan to do it very often.

The oil does 4500/5000km, as the manual says.
I'm really on point with oil changes and oil quality.

 

[BusyLittleShop]

What is more important?

Flow is more important... a 5/10w50 flows quicker than a 15/20w50 during initial start up temperature... however once the engine reaches operating temperature both flow the same grade 50 + or - a few centistrokes of gravity flow...

The sole purpose API ranks the first number (Example 10) and the letter W is to
inform the buyer the oils ability to flow during critical start up...

API ranks the first number 10 and the letter W from the newest to the
oldest on its ability to lube your engine during critical start up because
the most wear happens during startup before pressure is establish...

0W

5W

10W

15W

20W

If you wish to employ the latest in oil companies technology then you
want an one with an API low number rank...


Note... the W in 10W does not stand for "winter" W is just a designation of one type of testing vs another...

Quote Dr.Haas

"The W is just a designation of one type of testing vs another. I
personally asked them if it stood for "winter" and they flatly said "no".

Quote MolaKule

"W" stands for the oil's properties at 0 F and agreed, it does not mean weight or viscosity grade."

Oil pour test at -35c graphically showing oils properties before warm up when the 30 and 40 can flow in their respectable grades...

 

[ZeeOSix]

Note... the W in 10W does not stand for "winter" W is just a designation of one type of testing vs another...

Quote Dr.Haas

"The W is just a designation of one type of testing vs another. I
personally asked them if it stood for "winter" and they flatly said "no".

Quote MolaKule

"W" stands for the oil's properties at 0 F and agreed, it does not mean weight or viscosity grade."

It certainly does stand for "Winter". Another one sucked into the misconception tornado.

Thin vs Thick Discussion Chapter 1

A few things I keep hearing again and again: “The flow will be proper because its a positive displacement oil pump. The flow will always be exactly related to the RPM. It makes no difference what oil weight you use” This is Wrong. “0-30 is too thin, my engine requires a 10-30 oil.” Wrong again...

bobistheoilguy.com

Also ... see page 4: http://www.lelubricants.com/wp-content/uploads/pdf/news/White Papers/simple_viscosity.pdf

 

[BusyLittleShop]

It certainly does stand for "Winter". Another one sucked into the misconception tornado.

Negative... its does not stand for "winter" nor "weight" as popularly repeated...

 

[ZeeOSix]

Negative... its does not stand for "winter" nor "weight" as popularly repeated...

Sorry ... go search for the right answer and you'll see you're wrong.

Here's what Valvoline says about the "W" rating ... I think they know something about the history of motor oil.

Frequently Asked Questions - Valvoline™ Global

Whether you have questions about motor oil, our involvement in racing, or our business, you can find easy-to-understand answers here.

www.valvoline.com