Is 10w 40 oil ok in a 2 stroke gearbox?

429 Sterling
Posts
296
Joined
11/19/2023
Location
Boston, MA US

I have a ktm 250sx and have always used Motorex 15w 50 as the manual suggests. Accidentally got shipped a bottle of 10w 40. Will I be ok running this or should I just order a new bottle?

1
|
5/30/2026 11:14pm

Absolutely not. The bike will explode

8
Glory831Guy
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5/30/2026
Location
san francisco , CA US
5/30/2026 11:25pm

Owners manual for my 2002 Honda Cr250 smoker recommended 10-40, for what it's worth✊

runic121
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Bumfuck, OK US
Fantasy
5/30/2026 11:32pm

It's fine. It'll be fine. Run it. 

10
Tuplavee
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2/21/2021
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FI
5/31/2026 12:06am

I have used about the cheapest 10W40 with API SJ/JASO MA 2 rating in Austrian two strokes and YZ. Hundreds of hours

4
1

The Shop

BikePilot
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375
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9/27/2014
Location
Golden, CO US
5/31/2026 7:08am

It's fine but two stroke transmission oil (bell ray light gear saver) generally gives you a better clutch feel.  The bike will be fit with basically anything remotely like oil in there through.  This is not a sensitive application.  ATF works well too.  The 15-50 is my least facts I find it makes the clutch pretty slow to bite.  I think it's a bit thick and a two stroke doesn't generally put enough heat into the transmission to thin it out.  A 75w two stroke transmission oil seems much thinner and makes for a more responsive clutch.

4
AJ565
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3/12/2012
Location
San Antonio, TX US
5/31/2026 8:42am

The only oil I've ever run in my 250sx is Motul Transoil 10W40 and its currently at 190 hours.

3
1
ab5772
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709
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4/1/2008
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SLC, UT US
5/31/2026 9:16am

Rotella in every gearbox.

5
FeetUp
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Santa Maria, CA US
5/31/2026 9:58am

You’re gonna die

2
Falcon
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11/16/2011
Location
Menifee, CA US
5/31/2026 10:29am

10W-40 will be fine, as long as it's motorcycle oil. Don't put automobile oil in your gearbox.

2
dn315
Posts
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2/10/2025
Location
Allegany, NY US
5/31/2026 10:49am

Motul 10w40 is what I’ve always ran 

johnk408
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1/20/2022
Location
Ft Mitchell, KY US
5/31/2026 10:55am
ab5772 wrote:

Rotella in every gearbox.

Ditto

2
5/31/2026 11:27am

Motul 7100 10W-40-50 the higher number is better in extreme conditions and heat.

6/1/2026 9:07am

As long as it's wet clutch safe, you're good. 

kage173
Posts
3040
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11/27/2015
Location
TX US
6/1/2026 9:18am

That stuff is liquid gold. Run it. 

 

1

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