But the book says........

[Iver]

I'm just about to refill the oil in the fan drive gear box on our MC-9.
I assumed I would fill with 85w-90w gear oil.
But the book says 30w heavy duty engine oil.
What is most commonly used?

Also the book says 30w engine oil in the oil fill wheel bearings...........
      I used gear oil as others have said.
              Thanks,  Iver.

[pipopak]

Usually to follow the book is a good idea....

[Geoff]

I remember a few years back someone with an MC8 had a problem with the gear box oil foaming up and Southern Oregon Diesel figured out the previous owner had mixed detergent oil with non-detergent oil causing the foaming.  I run 10w-30 or straight 30w in my gear pump for the Sheppard steering with no problems.

[bevans6]

You only need "gear oil" for hypoid gears, like the gears in a differential.  Hypoid gear teeth are cut so the teeth slide over each other rather than just engaging.  Helical or bevel cut gears don't need the extreme pressure modifiers in gear oil, they are extremely happy with engine or transmission oil.  If you want to give it a treat, go find some synthetic transmission oil.  Bearings are happy with normal oil as well.

Brian

[bottomacher]

Is that synthetic automatic trans oil, or manual trans oil (if that even exists)?

[bevans6]

I was referring to synthetic manual transmission fluid, I have gotten it from motorcycle shops and from truck supply places.  I use SAE 50 in my Spicer 4 speed.  It isn't cheap but you don't need all that much either.  I would use it in anything other than the engine, the power steering and the differential that called for an SAE type engine oil.

http://www.imperialoil.ca/Canada-English/Files/Products_Lubes/IOCAENCVLMOMobil_Delvac__Syn_Trans_Fluid_50.pdf

is a good example.

Brian

[Jriddle]

I would follow the book. 80-90 weight would be very stiff in cold weather and would take some time to warm up. The belts may slip and become ineffective.

My Thoughts
John

[Iver]

Sounds like by the book it will be then.
     Thanks,  Iver