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Before changing out the hydro oil in 2 Gravely HD ZT 60's I googled what weight of oil to use, from Gravely. Says in the owners' manual 15W50. So I does that. Then one of you smart guys says "20W50". Crap! I want to do the right thing as one of the mowers belongs to my DIL and it a new mower. Changed at 48 hrs. Now I'm feeling guilty. Do I need to go back & drain it out & R&R with the 20W50? Or am I being ****?

bullet bob said:

Before changing out the hydro oil in 2 Gravely HD ZT 60's I googled what weight of oil to use, from Gravely. Says in the owners' manual 15W50. So I does that. Then one of you smart guys says "20W50". Crap! I want to do the right thing as one of the mowers belongs to my DIL and it a new mower. Changed at 48 hrs. Now I'm feeling guilty. Do I need to go back & drain it out & R&R with the 20W50? Or am I being ****?

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Do what the manufacturer recommends. Do not overthink it.

Hydrogear uses 20w50 from the factory, but also recommends using what ever the mower manufacturer recommends. I have seen mower manufacturers recommend 5w20,10w30,10w40,15w40,20w20,15w50. Hydrostats are a high pressure oil pressure pumping system, they are not married to any special weight of oil.

bullet bob said:

Before changing out the hydro oil in 2 Gravely HD ZT 60's I googled what weight of oil to use, from Gravely. Says in the owners' manual 15W50. So I does that. Then one of you smart guys says "20W50". Crap! I want to do the right thing as one of the mowers belongs to my DIL and it a new mower. Changed at 48 hrs. Now I'm feeling guilty. Do I need to go back & drain it out & R&R with the 20W50? Or am I being ****?

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There is not a vast difference that would cause an issue in the hydro system. It only gets critical when it comes to the use in a diesel engine, especially in colder climates.

Good deal guys. Appreciate all the comments. I'll quit worrying. Only thing that had me double-guessing was the fact that I was adding slight amounts to the reservoir, like ounces. Did the purge correctly. Thought that maybe I was somehow burning up some of the lighter oil. Just need to take a breath.......

bullet bob said:

Good deal guys. Appreciate all the comments. I'll quit worrying. Only thing that had me double-guessing was the fact that I was adding slight amounts to the reservoir, like ounces. Did the purge correctly. Thought that maybe I was somehow burning up some of the lighter oil. Just need to take a breath.......

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You will always have to add a little as all induce settles out.Quite of air can be introduced during the purge.

Besides the lower number is just so you have better operation at lower temps until the hydros heat up. IE the oil just flows better at lower with the 15w50 than with 20w50. Just want to make sure the oil use has a zinc additive; although, it is not necessary. Just help with the wear. It sorta like adding Moly to your old vehicle engine which re-coats worn bearings.

I use Mobile One 15w50 on most applications but do have the option of using a Valvoline XR1 20w50 oil.

Yes sir, the Mobile 1 15W50 was what I used. Thanks all!