Different weight oil in finals

[Pony]

G'day all;
Komatsu D31P-20 that specifies engine oil for all oils throughout the machine. I've only had it a few months and am going through and changing all the oils for peace of mind.
Can anyone see an issue with going to a gear oil (80-90 or 80-140) in the final drives?
My thinking is heavier the better in that application, but am far from being an expert.
Thanks

 

[Cmark]

Yes, there could be an issue. Gear oils generally have an EP (extreme pressure) additive which can contain sulphur. Sulphur reacts with the copper contained in some bronzes and if the final drive isn't built to run gear oil, it's not advisable to try.

If you want to experiment with something other than the OEM recommendation, try TO-4 spec transmission oils.

My personal feeling is that if you want to get the maximum life from your FD's, forget about tampering with the oil grade, just change it every time you change the engine oil. It will not cost much and only take about 20 minutes. Time well spent IMO.

 

[Pony]

Yea rightoh, this might have been a case of knowing just enough to get myself into trouble. I thought that a heavier weight oil would be better in the finals, didn't think it could cause any issues, good thing I asked first. I dropped the old oil out and it was engine oil rather than gear oil and it was pretty clean with just a little bit of very fine metal on the magnetic drain plug.
Looks like I'll put engine oil back in there, thanks again.

 

[Karl Robbers]

Yes, there could be an issue. Gear oils generally have an EP (extreme pressure) additive which can contain sulphur. Sulphur reacts with the copper contained in some bronzes and if the final drive isn't built to run gear oil, it's not advisable to try.

If you want to experiment with something other than the OEM recommendation, try TO-4 spec transmission oils.

My personal feeling is that if you want to get the maximum life from your FD's, forget about tampering with the oil grade, just change it every time you change the engine oil. It will not cost much and only take about 20 minutes. Time well spent IMO.

I had this unfortunate experience. Twice.
Thankfully it was not a dozer final drive, but a rebuilt Land Rover gearbox. There is a large bronze bushing on the main shaft. Twice this failed due to the gear it carried seizing onto the bush.
I cannot quite remember the exact details of how I came to be talking to the oil rep about this gearbox, but it transpired that the oils recommended by most of the oil companies were in fact incorrect, but few experienced the problem due to most gearboxes in service being worn sufficiently that the issue never presented. Once the gearbox was rebuilt the third time and the correct oil used, no problem.
I am very careful with oils since then.

 

[Willie B]

My Dresser calls for 80W140 in the finals. I think use what the manufacturer calls for. Likely they have spent considerable time, research, and education deciding what they want. You may want to check to see if a service bulletin has changed the recommendations.

Willie

 

[kshansen]

Another thing some don't know is that 80W-90 is not that different in viscosity from say a 50 weight oil. Motor oil, transmission (TO-4) and gear oils are measured different. Of the top of my head I believe 80W-90 is only about the same as a 50 weight engine oil so not that big a difference.

And on the idea of using a heavier oil than called for could actually cause lack of lubrication due to oil not flowing into the critical areas.

 

[Nige]

Another thing some don't know is that 80W-90 is not that different in viscosity from say a 50 weight oil. Motor oil, transmission (TO-4) and gear oils are measured different. Of the top of my head I believe 80W-90 is only about the same as a 50 weight engine oil so not that big a difference.

And on the idea of using a heavier oil than called for could actually cause lack of lubrication due to oil not flowing into the critical areas.

Ken's correct. Actually an 80W90 is somewhere between an SAE 40 and a 50 in motor oil viscosity terms. A lot of people don't know that the two types of oil are measured using different scales.

 

[Old Magnet]

Here's a handy comparison chart.....

 

[nowing75]

I learn somthing new everyday

 

[Nige]

Excellent chart from OM. The one thing it doesn't show is how modern SAE 60 power train oils (measured in engine oil viscosity range) stack up against gear oils. IIRC it's somewhat similar to an EP140.

 

[Pony]

Rightoh I'm convinced, maybe the engineers at Komatsu do know a bit more than me.
I thought the single oil throughout was to make it idiot proof against putting wrong oils in wrong places and that by going to a dedicated gear oil in an extreme pressure item like the finals could only be a good thing.
Thanks again for the good advice.

 

[Dickjr.]

My Komatsu reference guide shows a -21 model using 30 engine oil. I recently changed my d39EX-21A and used 30 Engine oil as according to the chart.