Why does my Isuzu specify engine oil for use in manual transmission? Can I use 75w80 gl-4 instead?

[ripcord]

Folks should know that they shouldn't substitute gear or motor oil in manual transmissions that call for ATF. Those units will often have needle bearings that require a low viscosity lubricant or sometimes they have clutch type synchros that need the properties of ATF.

 

[MolaKule]

Hello ladies and gents,

My isuzu d-max has a 5 speed manual transmission. But when I look at the manual it specifies a very specific Besco 5w30 transaxle fluid OR 15w40 CI-4 engine oil (Delo 400 15w40, Mobil 1 delvac mx 15w40 etc.) and researching around tells me that Isuzu likes to put engine oil in their manual gearboxes.

Wouldn't a gl-4 fluid be better suited for this function? I'm curious to try 75w80 gl4 in my light diesel truck but would want to ask around first if its a good idea. According to other Isuzu forums, their recommendations are to use 5w30 C3 or 10w30 engine oils but I wonder if the additives for the engine would be good enough as opposed to a purpose built MTF/MTL fluid.

The 5W30 motor oil suggestion was in LIEU of MTF if MTF could not be found.

The next group of MTL’s are in the 9.6 to 10.x cSt range (SAE75W80):

1. Redline MTL 75W80
2. Amsoil MTF
3. GM Synchromesh Series
4. Volvo MTF 645
5. Fuchs TITAN SINTOFLUID SAE 75W-80 synthetic MTF (Carries a GL-5 rating as well)
6. Lodexol (Morris Lubricants) MTF
7. Motul MotylGear 75W-80 GL-4/GL-5
8. HPL Manual Transmission Life 75W80

Thread 'Updated List of MTFs'

May 30, 2024

Updated List of Manual Transmission Fluids Updated May 30th, 2025

NOTE: This list is only a “summary” list of MTFs available in the MTF Lubricant Market and only available in US auto parts stores and US Import outlets. It is not an endorsement nor a critique of any one fluid, nor is it implied that any one fluid will cure problems in MTs that have design problems or those that have excessive wear. Viscosities listed are at 100C and rounded up.

A.These MTL fluids are closest to a Kinematic Viscosity of 6.X cSt@100C (About the same viscosity as Dexron VI ATF) LV MTF's:

1. HPL Manual...

• MolaKule
• Replies: 0
• Forum: ATF, Differential, Trans, Brakes, P/S

• 
• 
•