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  1. #1

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    Oil pump vs Premix? '95 Polaris SLT 750

    '95 Polaris SLT 750. Let's put this to rest once and for all! I'd like to hear from everyone on their personal experience and I'm sure the experts will chime in. Which is the better way to go with the oil pump or premix? Depending on your answer please let me know which is the best oil to get by with. I know you get what you pay for. Just keep in mind I've got access to Wal-Mart Mercury Quicksilver PWC 2-Cycle Oil (regular $27.97 gal and synthetic 37.97 gal), Academy has a Mystik JT-4 Synthetic 2-cycle Personal Watercraft Engine Oil (only 24.99 gal). Just some choices I've seen in my area. I've heard recently from a very good source that these machines were prone to the oil pump failing and taking that part out of the equation and going premix is the way to go. Is this true? Don't you use more oil when premixing? One other thing be sure and mention if you choose either premix or oil pump. Which oil to use for each? What ratio do you premix that works best for your ski or mine. I hope to have my ski up and running this spring/summer and would like to know which way is the most reliable and least expensive route to go. Thanks for all your feedback.


  2. #2
    David
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    I have always chosen to KEEP THE OIL INJECTION it will greatly reduce the amount of oil you use, and you will not have to worry about getting gas at a marina..and not having oil to mix.....also the pain of mixing oil I have never seen an oil pump fail. the most common problem is the oil line falling off its connection, but if you use new lines, this should also not happen. I personally use Polaris Blue oil and it has never been an issue for me...that I know of...engine still runs LOL

  3. #3

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    Original oil pump in my '94 SLT 750 still working great. Just keep an eye on the hoses... no kinking or leaking and tight connections.

    I much prefer oil injection. Pre-mixing is a pain... and I have lots of family use the ski and I'm sure someone would forget to pre-mix... so I don't have that worry.

    I like Cabela's semi-syn 2-stroke oil... ~$20/gal. Burns clean... minimal smoke... smells fine.

    Cheers!

  4. #4
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    Quote Originally Posted by bwhitsonjr View Post
    ... Let's put this to rest once and for all! ...
    Not possible.

    Pre-mix is a 'thing' for many 2-stroke owners. They like it that way, and they will do it that way!

    This subject has been walked around the forum many times. The factory oil injection system on Polaris 2-stroke watercraft tends to be quite reliable. Both Fuji and domestic engines.

    Other brands of watercraft seem to have a more difficult history with oil injection. Not sure of all the reasons, but that seems to be the story.

    If you look at the actual causes of engine damage among the threads and posts on here (where the cause is at all clear), the vast majority are not oiling failures. Most are caused by owner neglect and fuel system/carburetor issues. And just plain old mechanical wear and tear over time.

    The Polaris oil injection system is quite easy to maintain. On the domestic engines all the components are out in the open where you can see them. Not hard to inspect the hoses, check the clamps, etc. The Fuji oil pump is hard to inspect since it is down low on the side of the engine, but an inspection mirror or camera and some careful fingering can confirm it is still hooked up and the clamps are in place.

    On some engines the oil feed nipples on the engine have check valves inside (3083337/3086785). Those check valves need to be clean and working. Spraying some solvent through them is usually enough to confirm they are clear.

    On engines with variable rate oil pumps (all domestic engines and all Fuji engines where there is a linkage to the throttle from the oil pump (item 5 in the attached diagram) the oil consumption will be about half of the oil used with pre-mixing. Looking at it from a cost standpoint, you can afford to buy much better oil when using oil injection, since you will be using it half as quickly.

    The pre-mix ratio typically used is 40:1. Some owners use other ratios.

    There have also been many threads and opinions on oil quality and brands. Generally speaking you want an oil that is much better than the minimum specification TC-W3 outboard motor oil. TC-W3 is an antique oil spec and is no longer very useful for choosing a good oil. Look for a higher oil specification on the oil, ISO EGD or JASO FC ratings are a good starting point.

    Click image for larger version. 

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    Last edited by K447; 04-04-2013 at 10:43 AM.

  5. #5

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    I can only comment from an outboard perspective and my limited understanding on my 780. With outboards a pump failure will not starve the engine of oil, they allways over oil and looking at the pump diagrams I would say the same would happen for the ski (correct me if I am wrong). Oil lines will always be an issue with any oil injection system especialy when they get older. The only other thing that concerns me with the ski is the nylon clips that link the pump, rod and carbs together. I would replace those aswell. The main differance between the two is how the oil is mixed. On most outboards it is injected into the fuel system before it enters the carb which seems a safer method to me and would mix better imo. I am on pre-mix but that is only because the ski I have has never been run using the injection system. I will soon be piping the injection pipes into a seperate bottle and running the ski for a good few sessions still on premix to determine if the system is working correctly. I will be able to monitor the quantity accurately for the amount of fuel used. I would expect an average measument of around 100-1 mix for moderate speeds. Personly I would sooner run the oil injection as its less hassel and lets be honest, oil is expensive. Also theres nothing worse than the smell of an over oiled 2 stroke.

  6. #6

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    Auto Culto - If I recall correctly if there's a linkage failure on the Polaris the oil pump reverts to full-on mode on the oiling. If a line breaks or falls off, motor is toast.

    K447 - great perspective on the premix or not question.

    Convenience or peace of mind - thats the basics of the crossroad here - decide your risk tolerence level and go on.

    Oh and one last thought - oil is expensive - but a new motor is a lot more expensive

  7. #7
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    Quote Originally Posted by showmepro1200 View Post
    ... oil is expensive - but a new motor is a lot more expensive
    Actually, have you done the arithmetic?

    Over the expected lifespan of an engine, how much oil would it consume, in dollars?
    There are two numbers, one if using oil injection, another, larger number if using pre-mix.

    Take those numbers and compare it to the cost of an engine rebuild.

    Now, the engine will eventually wear out anyways, even with good oiling. So when you are half way through the life of the engine, the 'cost' of an engine failure at that moment due to an oiling failure is effectively only half the total value of the rebuild.

    Back of the envelope numbers;
    Engine rebuild $1000 (SBT charges $600 to $1200, depending on the engine size)
    Expected engine life between rebuilds, say 200 hours (maybe more, maybe less)
    So the engine itself costs $5 per running hour

    Fuel consumption, as a method for estimating oil consumption;
    Varies depending on the engine, of course, and how hard it is ridden.
    I shall calculate using 6 gallons per hour (complete guess on my part)
    6 gph times 200 hours = 1200 gallons of fuel between engine rebuilds

    40:1 premix would be 1200/40 = 30 gallons of oil

    Cost of oil at $30/gallon is $900 (if you can get it that cheap).
    Buy better oil and the total oil cost is greater, of course.

    So the oil you burn costs about as much as the engine itself

    If you use oil injection then you save roughly $400 (you could/should use better oil, so not quite 1/2 the cost of pre-mixing), which would pay for about half the engine rebuild cost.

    If you can get 400 hours between rebuilds then oil injection will save you enough to effectively pay for the next rebuild.

    Oh yes, fuel costs.
    1200 gallons at $4 each = $4,800
    If gas costs only $3 per gallon that is still $3,600

    Find a way to cut fuel consumption by 25% or more and it pays for every worn out engine rebuild.

    How can you reduce fuel consumption? :

    Choose your engine carefully

  8. #8
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    For those that are familiar with the various Polaris watercraft engines (stock), try listing them from most fuel efficient to least.

    I suspect some people will be surprised at where their model slots in.

  9. #9

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    If premix is 40:1, then what ratio is the oil pump supplying at full output ie full throttle? 40:1 as well?

  10. #10
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    Quote Originally Posted by BlueFishCrisis View Post
    If premix is 40:1, then what ratio is the oil pump supplying at full output ie full throttle? 40:1 as well?
    That has been the baseline estimate. The engine tends to need max oiling only in the upper RPM and power ranges.

    I don't know if there are any actual data from Polaris in this regard, nor do I know if they altered the oil pump curve between the domestic and the older Fuji engines.

    If I had to guess, I would think the early Fuji engines (non-variable rate) were running on the oil heavy side, since nobody had long term data from engine wear on these things in the early days. Certainly somebody had to figure out what curve to use when they changed to the variable rate Fuji oil pumps.

    Note: People tend to think of oil in terms of fuel-oil ratio, but that is just a shorthand to make it easy to pre-mix the oil into the fuel.

    If you take a given engine and figure out a way to make it run more fuel efficiently, the oil requirements do NOT change just because it is using less fuel. The bearings and cylinder walls need roughly the same amount of lubrication as before, but since you are burning less fuel the calculated fuel-oil ratio changes. The oil consumption/needs of the engine has not.

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