GRAVELY specified 10W-30 for 8000-Series, then later changed to 10W-40 motor oil for G-Series. I've heard people recommend "gear oil" but the trend has been for motor oil to be used. I was in disbelief back when SAAB switched from traditional extreme pressure 80/90W hypoid gear oil to multigrade motor oil for 900 Turbo 5 speed transaxles!
I just changed my 16-G partzer's tranny oil & looked thru GRAVELY literature, basically asking the same Q. Only saw multigrade motor oil specified all the way back. Had thought perhaps 800-Series might've called for "gear oil" & that was sticking in mind. Not so. Part of my dilemma was I have most of a 5Gal bucket of "gear oil" left over from a Farmall project & had to go to WallyWorld for 10W-40.
For me I was presented w/terrible 'Yohoo' looking old motor oil & suspected water had gotten mixed in. It was also overfilled, but once drained I couldn't detect any water separating out or metal debris at bottom of drain pan. Was also puzzled by capacity. GRAVELY says 6 Qts, fill to level plug, do not overfill. However what I drained fit a 5 Qt & the new 5 Qt filled it almost to the point of pouring over the edge of the level plug.
I noticed you're in Maine & would expect "gear oil" to be at least as Thick As Molasses on cold winter days, perhaps even thicker. Also presume you think its time to change oil? Or is your Q whether you need to get rid of the "gear oil"? IMO if the "gear oil" looks real good & cold temp viscosity isn't an issue, why change it until its due? Can the previous owner illuminate how old the oil is? Lots & lots of oil is changed needlessly in the US, while many other countries use oil analysis to tell them when to change.
One Quick & Dirty oil analysis I've practiced is to sample the oil at the drain plug. All you do is loosen the plug carefully & just barely open it a crack, so as to capture a small amount of 'Bottom of the Deck' oil out of the sump & immediately screw the plug back in. Inspecting this oil can detect if any water got inside or if there's metal debris.
When you do change oil a TIP is to insert a small magnet thru the drain plug hole. It'll stick to the inside of the tranny case & collect steel debris, removing them from circulation in bearings/gears.
Use the 10w40 oil as per the manual, If you are not sure where the unit was kept before it became yours, change the trans oil. If you are going to keep it stored in side and use it year around change it every 2 to 3 years.When you fill the trans. just remove the plug from the oil level indicator (on the left axle front side is a short pipe with a 90 deg. elbow with the plug in it) fill the trans. until the oil is level with the top of the elbow.
The transmission will collect condensation so thats why I sugest changing it now. It could freeze up real quick in the warm climate up there.
Had an old ford tractor that would freeze up the rear end every winter.
That is a good looking tractor and the engine guard is a great add on.
Yes, I'm going to change the fluid. Not because the wrong fluid is in there, but I like to have a "baseline" of maintenance when I buy any vehicle. If I bring the scheduled maintenance up to current, and change all the fluids, then I know when things were done, when fluids were changed, and what fluids are in there.
Yes, I will be using this year round, stored in an unheated garage -- so the gear oil will be too heavy for the cold months.
my manual for my 816 calls for a SAE 30 (which is just a heavy duty 30 weight motor oil) for year round use. My suggestion - do as the manual says. The way i figure is that Gravely knows/knew more about those tractors than I do.
Bumping an old thread since this is the topic I have a concern about.
Modern oils have changed. Refering to an old owners manual may not be the best solution. You can email redline oil company and give them info on what you have and what the "old" manual said. They should email back with modern product that may be "better".
Also redline website and I think amsoil does as well describes how a gear oil of x weight compares to oil weights.
Over the years Gravely has speced many things for in the tranny. From ATF all the way up to SAE 90 gear oils. Thing to remember about gear oils is that the viscosity of a 30 wt motor oil is about the same as 90 wt gear oil.