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We have a second hand Hustler Super-Z zero turn mower, for which I need to top up the hydraulic oil.

The mechanic when he serviced it, gave us two types of oil 10W30 and 10W60 and told me not to put the wrong oil in.

But I've forgotten which is for the engine and which is for the hydraulics.

The number before the letter ‘W’ denotes the viscosity in cold temperature, usually of zero degrees. The oil becomes viscous when the temperature is cold. So, it means that the engine oil rated OW20 will circulate more quickly throughout the engine as compared to oil with 10W ratings. Though the 10W rating engine will start the car, OW will not take that much time to warm up the engine.

Now, the second number shows the viscosity of the engine while running at up to 212 degrees https://carfromjapan.com/article/car-maintenance/10w30-vs-10w40/

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    Welcome to Motor Vehicle Maintenance & Repair! I take it your question is, which oil is for which? You don't specify this in your question. I'd venture to assume the 10W30 is for the engine. Never heard of a 10W60 and would never use that in an engine, so that must be the oil for the hydraulics. I'm surprised the mech didn't give you something which was labeled as hydraulic oil.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Oct 30, 2022 at 23:53
  • @Pᴀᴜʟsᴛᴇʀ2 thanks, I also realized that by the amount of oil used in the oil change (1L vs >4L) the 10W30 must be for the engine. The 10W60 says it's for super cars btw
    – Tom Huntington
    Commented Oct 31, 2022 at 2:34

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According to one online resource for the operator's manual of the Hustler Super Z mower, p. 26:

IMPORTANT: Never use hydraulic or automatic transmission fluid in this system; use only motor oil as specified. Remember, dirt is the primary enemy of any hydraulic system.

Additionally, p. 27 provides service grade specifications for the oil:

Fluid level should be 1" from top of reservoir. Use only SAE 10W40 SG, SF/CC, CD service motor oil.

p. 15 contradicts this information:

  1. Hydraulic system capacity is 5 US quarts of 20W50 motor oil. Fill reservoir to within 1" of top of Item 3 (032771 Strainer). See "Hydraulic system" on page 10-24.

The above reference appears in the assembly section of the manual and may represent an initial filling. No other reference was found with respect to draining and replacing the fluid, however.

The only reference for engine oil specifications is "check the owner's manual" for your specific engine.

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