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Discussion Starter · #1 ·
Headed off to my local JD dealer to purchase some Cool-Gard II premix antifreeze and some Gear Lubricant for my 54D MMM. I thought I had researched, read the manual, checked Greet Tractor Talk, etc enough to make a couple of informed purchases. I was after some GL-5 Gear Lubricant. Uh Oh!!! I didn't think about which viscosity. So I asked the parts guy, I told him it was for my 54D mower under my 1025R. He thought for a moment, then replied 85W-140.

Hmmm They had 80w-90; 85W-140; and 75W-90 SYNTHETIC

So I bought his recommended 85W-140. Now having second thoughts. Should I have bought the 80w-90? Am I overthinking this?
 

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It really doesn't matter, they all will work. The W is the cold temperature viscosity and the 75w is what you want when you are cutting at temps below zero. The other number is the warm weather viscosity and is more what we normally are concerned with for lawn mowing. The thicker the oil, the better it will handle the load with a reduction in economy and Power available. I use the 140 as my 1026R and the 445 can handle the power penalty. My 445 is a 1994 vintage and the gear box is original.
 

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Since the mower deck is typically run in the hottest months of the year, I think the higher viscosity will be fine. Personally, I tend to go towards Synthetic Fluids myself.

There is quite a difference between a 85w to 90w viscosity and one which is 85w- 140w. The minimum viscosity of any of the 3 choices should be the lowest number listed, which were 80x, 85w and 75w in your examples. It's the higher viscosity of 140w which is significantly "heavier" than the other two options.

That means the 140w gear oil is going to be heavier when you start to use it when cold, than would the other two choices with highest viscosity of 90w. One important thing to remember about "Gear Oil" in this application is the gears are immersed in the oil and remain immersed the entire time. The point is, the gear oil is lubricating the second the gears start to turn, because the gears are 1/3rd or even 1/2 submerged in the gear oil in the case at all times.

Engine oil has to be pumped to provide lubrication to the parts. This gear oil is surrounding the gears and they are spinning in it the moment you turn on the PTO. Since the deck is used during hot weather, I think the heavier oil won't hurt a thing. You sure wouldn't want the 140w gear oil in something used in winter as that would be thick enough to hold a wrench vertical in it when winter month cold........ ;) So don't mow in the snow......
 
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There is no such Gear Oil in the GL-5 group listed as 140W. This would be 140 and is the hot oil viscosity. With Multi Viscosity oils, the first number is the cold oil viscosity and is measured at a specified temperature and the second number is the viscosity when the oil is at a specified hot temperature. 85W-140 is the correct nomenclature. This is what I use in all my equipment used in the warm temperatures of Spring, Summer and Fall. If I can find it, I use the 75W-90 Synthetic in the Snow Blower.
 

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Discussion Starter · #6 ·
I appreciate yall's replies. I returned to my dealer this afternoon and exchanged the 85w-140 for the 80w-90. Funny, it was thirty cents more for the 80w-90, and when I asked why, he replied it's much more common than the 85w-140. So there you go. Should have researched this a bit more prior to purchasing. But now I know.

Also, in doing all this research, I discovered my vent valve JP5801 was missing the top vent plug that keeps dirt, debris and water out. So I was able to order a couple of those also.

Thanks again for all your replies. And, no - I won't be mowing in the snow. lol
 

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It's not the viscosity that's important with gear lube. It's that wonderful smell.
 
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