The ratio of fuel blending used in the stroke push mower determines its performance and lifespan. Consider standard industry guidelines for reference. The default blending ratio is 50:1 (add 20 milliliters of engine oil per liter of gasoline) or 40:1 (add 25 milliliters of engine oil per liter of gasoline) of gasoline and two-stroke special engine oil, depending on what the manufacturer recommends. For example, the Husqvarna LC 140 model requires a 50:1 mixed oil, and some of the older models such as Toro Recycler may require 40:1 to enhance lubrication. When the mixing ratio deviates more than ±5% (e.g., when oil concentration is below 45:1 or above 55:1), it can cause wear rate of cylinder wall to rise by over 30%, and even cause piston rings to become stuck due to lack of lubrication. It can cost the maintenance up to 40% to 60% of a new machine.
From a cost perspective, hybrid fuel costs increase by approximately 15% compared to pure gasoline (given the cost of engine oil is $0.1 per milliliter and the cost of gasoline is $0.8 per liter), but can significantly reduce the failure rate. According to a research by the United States Environmental Protection Agency (EPA), an optimally blended mixed oil can reduce the particulate matter emission of a 2 stroke push mower by 22% and improve fuel efficiency by around 12% at the same time. For example, following prolonged use for 1 hour, the Troy Bilt TB20’s fuel consumption with 50:1 mixed oil is 0.5 liters per hour. But under the same working conditions, the machine that uses pure gasoline in a wrong way may have its fuel consumption increase to 0.65 liters per hour, and its average service life shortened from 8 years to less than 5 years.
In terms of environmental and operational risks, partially combusted mixed oil can release polycyclic aromatic hydrocarbons (PAHs) at concentrations up to 120 µg/m³, which is 50% higher than the EU non-road machinery emission standard limit (80 µg/m³). Additionally, if the viscosity of the engine oil is not compatible (e.g., applying four-stroke engine oil in a wrong manner), it will increase the likelihood of clogging the carburetor nozzle by 40%, and the maintenance cycle will be from once a year to three times. The 2021 report by the Australian Consumer Council states that complaints against 2 stroke push mower faults caused by fuel issues accounted for 34% of the complaints under the garden machinery category in the year, while 70% of the cases involved incorrect mixing ratios or low engine oil.
Caution should be exercised with temperature adaptability in the user operation manual. In a hot climate (>35°C), it is recommended to increase the engine oil ratio to 45:1 to prevent knocking. When the temperature drops to low temperatures (<10°C), lower viscosity engine oil (like JASO FB standard) should be used to maintain the cold-start success rate over 95%. As an example, the start-up time of the Stihl BG 56 model using 10W-30 two-stroke engine oil under -5°C conditions can be minimized to 3 times of its pull rate, while standard engine oil is more than 5 times. Apart from this, the mixing time of mixed oil should never exceed 30 days; otherwise, gasoline oxidation will lead to a loss in the octane number by 8% to 10%, which affects power output stability.
Finally, fuel mixing accuracy depends on measurement equipment. Using a calibrated mixing pot (with an error of ±2 milliliters) increases reliability by 90% compared to the visual inspection method, avoiding the risk of pot pulling caused by concentration deviation. According to industry reports, the average annual use cost of a well-maintained 2 Stroke push mower can be contained within 50 US dollars (fuel and maintenance), while the additional cost incurred due to fuel issues can go up to 200 US dollars per annum. For instance, tests conducted by “Consumer Reports” in 2022 found that models using 50:1 mixed oil properly still maintained a second-hand residual value rate of 35% of the new machine’s price after five successive years of operation, which was much better than the 15% when the maintenance was improper.