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30 or 40 weight oil?

Discussion in 'Mechanic and Repair' started by Vibe Ray, Aug 9, 2001.

  1. Vibe Ray

    Vibe Ray LawnSite Senior Member
    Messages: 785

    Hey guys, I was wondering when should you use straight weight 30 and straight weight 40 oil? I am using straight weight 40 oil right now, but am curious as to whether or not I should use SAE 30 oil. Thanx!
  2. Fish

    Fish LawnSite Member
    Messages: 139

    30 wt is recomended for air cooled engines, Where do you readily
    find 40 wt? Some engines with hydraulic lifters require a multi
    viscosity oil, but Never use 10w40 in anything!
  3. Vibe Ray

    Vibe Ray LawnSite Senior Member
    Messages: 785

    I am getting Pennzoil SAE 40 pretty much from anywhere I go around here. (K-Mart, Wal-Mart, Auto stores, you name it). What happened is I read the Kawasaki manual and looked at the chart to determine what type of oil I should use and it looked like Sae 40 would work best for my application cuz we get pretty hot down here. But I never here anybody using straight weight 40 and I was wondering why not. Am I using the wrong oil? Anyone able to let me in on the truth?
  4. wesley daniel

    wesley daniel LawnSite Member
    Messages: 6

    The part 5w,10w,15w ect. is the viscosity of the oil. 30w 40w 50w is the weight. A 5w 40 has the viscosity of a 5 weight oil but
    the protection of a 40 weight oil and so forth.Up north where it is colder you need a lower weight oil.If you ever noticed the lower the weight the easier it poures. When you run the motor a while it heast the oil up and it will pour real fast.
    When you first start a motor a straight 40w will be thick and wont flow to the bearings right away because it is thick, and the motor is cold if the ambiant temp. is below 75 . But a 10w40 will flow because it has the viscosity of a 10w oil,and will protect the bearings at colder temps.
    Your climate is about the same as houston . I run a 10w30
    in the winter and when the temp sticks around 70 I run 30w When it gets and stays above 90 I run 40.

    Hope this helps.
  5. Fish

    Fish LawnSite Member
    Messages: 139

    But NEVER use 10w40 in an air cooled engine!
  6. plow kid

    plow kid Banned
    Messages: 516

    I run 40w in everything now, I get it at Tractor Supply Co [ TSC ]
    it comes in 5 gallon buckets for $21.95, I see a increase in oil pressure with strait 40w over 10w-40
  7. sdwally

    sdwally LawnSite Senior Member
    Messages: 386

    We use four different types of oil for all our equipment: 30wt, mainly in all engines; 10w40, some hydraulic systems and a few engines; ISO 068(Turbine Oil), hydraulic systems(mainly Toro); and Hydraulic/Tractor Fluid, hydraulic and tractor transaxles.
    30wt Heavy Duty motor oil is a good all around engine oil that works well in all US areas. Multi-weight oils can be used, but are mainly for areas where wide temperanges exisit, below freezing to extremely hot. Not to slam Wesley, but he is not quite right about what multi-weight oils are. For 10w30, when the oil is cool/cold its viscosity is 10 weight(thinner, flows easier) and when it is at normal engine operating temp its viscosity is 40 weight(thicker, better protection for bearings since it will not be splashed away as easy). In extreme cold weather it is important to have an oil the flows easier and not be to thick to flow like honey.
    Synethics work pretty much the same way, except the do not break down under extreme heat conditions like standard petroelum based oils do. Note many new hydro systems that require synethic oil, means they generate or retain more heat than the other hydro systems.
    It is also important that you don't mix brands of oil, when added oil. Some brands have additives that don't mix well. I have seen one engine that had what ever the cheapest brand of oil added(oil changes not to often) that siezed. After splitting the case, all the oil had solitified in the bottom and was the consistancy of butter. Not a pretty sight! This is very rare, but can happen.
    The main thing to remember is to use oil that is equivalent or better than what the manufacture recommends.
  8. Fish

    Fish LawnSite Member
    Messages: 139

    When 10w40 breaks down it is very nasty, usually ruins the
    crank and whatever bearing it seizes first. 30 wt does not break
    down, which is why I recommend it over multiweight oils, except
    in very cold weather or where hydraulic lifters need it, but never
    10w40, it is the most prone to multi-viscosity breakdown.
  9. Vibe Ray

    Vibe Ray LawnSite Senior Member
    Messages: 785

    Does any brand make a fully synthetic SAE 30? I see 10w- 30, but not SAE 30 in synthetic. I wanna change over to synthetic next oil change (@100 hrs). What about a fully synthetic SAE 40?
    BTW, thanx for the help guys.
  10. Eric ELM

    Eric ELM Husband, Father, Friend, Angel
    Messages: 4,830

    I see Fish doesn't like 10/40 oil.

    What is your opinion on Rotella T 15/40 oil? I have used it in my diesel Chopper for the past 600 hours and also in my old Kohler that has almost 3,600 hours on it, for the past 700 hours. It sounds like a new engine. I ran it in the Hot summer, the Cold Fall and Spring also. I do let it warm up before cranking the rpm's up to around 3,750 though.

    I ran this same oil in my John Deere 430 last winter for plowing snow also. It cranked up like it had straight 5 W in it.

    I would be interested in hearing from everyone that has replied here on this oil.


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