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Just was reading this manual => DLE-120 engine User Manual

On this page (pg 4), I saw this formulation:

enter image description here

What does it mean? How is the 30:1 ratio calculated? What does "fl oz" mean? What does "2-cycle oil" mean? Where are these number coming from?

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    $\begingroup$ "fl oz" is a cruel and archaic imperial way of torturing people wanting to measure volume. $\endgroup$ – Jpe61 Mar 29 at 20:35
  • $\begingroup$ An amusing aside: once I watched an early Simpsons episode (the one where Homer's license is suspended due to DUI) with Spanish subtitles on. They translated "128 oz Supperware" (actually volume in fluid ounces) as "3.6 kilograms" rather than "3.78 liters". I think it roughly correlates to 1 fluid ounce of water weighing close to 1 ounce. Ain't Imperial units fun? $\endgroup$ – Phil Perry Mar 30 at 16:16
  • $\begingroup$ Specifically that's a US gallon and a US fluid ounce; there are others, though the Imperial (UK) gallon is no longer widely used; that engine is sold in the UK. Also note the spurious precision in the metric conversion of the oil (an extra decimal place compared to what the fl oz would give you). As that's a model engine, you're not likely to be mixing vast quantities; one drop of oil is around 0.05ml, so you couldn't be that precise anyway. $\endgroup$ – Chris H Mar 31 at 12:01
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What does mean "fl oz"?

"fl oz" means fluid ounce (1 fl oz ≈ 30 ml), which is a unit of volume, as opposed to dry ounce, which is a unit of mass.

How are they calculated the 30:1 ratio?

By ratioing 128:4.26, it is 30.05:1, so 30:1 is a good approximation

What does mean "2-cycle oil"?

It is oil for 2-cycle/stroke piston engines

from where these numbers have came?

Probably some design specs/limitations. You have to ask them if you want the details.

What does it mean?

That when you refuel, for every 30 parts of fuel you put in the tank, you need 1 part of oil for correct lubrication of the engine.

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Worth noting: when instructions say 2-cycle or 2-stroke oil, make sure you use this specific oil type. Just any oil will not be ok, in worst cases using wrong type of oil will cause the engine to seize.

I bet some numbnut will rush here to "say I've flown hundreds of hours with just regular 10w40", but, nope, it's not ok:

Wikipedia: Two-stroke oil

Comparing regular lubricating oil with two-stroke oil, the relevant difference is that two-stroke oil must have a much lower ash content. This is required to minimize deposits that tend to form if ash is present in the oil which is burned in the engine's combustion chamber. Additionally a non-2T-specific oil can turn to gum in a matter of days if mixed with gasoline and not immediately consumed.

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  • $\begingroup$ This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review $\endgroup$ – Abdullah Mar 30 at 14:20
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    $\begingroup$ @Abdullah this answer adresses the "What does "2-cycle oil" mean?" portion of the question. Other aspects of the Q are perfectly adressed by Federico's answer. $\endgroup$ – Jpe61 Mar 30 at 15:17
  • $\begingroup$ discussion on meta $\endgroup$ – Federico Mar 31 at 10:21

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