Car Engine Oil Ratios Worksheet for 15-Year-Olds | English & Math Practice

Instructions

Read the texts and answer the questions that follow. For the math section, show your work where appropriate to understand the steps involved.

Part 1: English - Reading & Vocabulary

In most modern cars, the engine is a four-stroke system. This means oil is kept in a separate reservoir and circulated by a pump to provide lubrication, reducing friction between moving parts like pistons and cylinders. However, many smaller engines, such as those found in chainsaws, leaf blowers, and some older motorcycles, are two-stroke engines. These engines are simpler and lighter, but they lack a dedicated oil circulation system.

To ensure proper lubrication, oil must be mixed directly with the gasoline. This creates a fuel-oil mixture that is burned during combustion. The specific amount of oil to fuel is expressed as a ratio, for example, 50:1. This means for every 50 parts of gasoline, you must add 1 part of oil. Getting this ratio correct is critical. Too little oil (a "lean" mixture) will not provide enough lubrication, leading to increased friction, overheating, and potentially catastrophic engine seizure. Too much oil (a "rich" mixture) can cause excessive smoke, foul the spark plug, and leave carbon deposits, reducing the engine's efficiency and performance.

1. Vocabulary: Based on the text, define the following words in your own terms.
   • a. Lubrication:
   • b. Ratio:
   • c. Combustion:
2. Comprehension: Why do two-stroke engines require oil to be mixed directly with the fuel?
3. Analysis: According to the text, what are two specific negative consequences of creating a "rich" fuel-oil mixture?
4. Critical Thinking: A 50:1 ratio has less oil per gallon of gas than a 40:1 ratio. Which mixture would be considered "richer" in oil? Explain your reasoning.

Part 2: Math - Ratios & Calculations

Use the information from the reading and the questions below to solve the problems. Remember, there are 128 fluid ounces (fl oz) in 1 US gallon.

1. Basic Calculation: You need to prepare a 5-gallon container of gasoline for a boat that requires a 50:1 fuel-to-oil ratio. How many fluid ounces of oil do you need to add to the 5 gallons of gas?
2. Working Backwards: You are mixing fuel for your leaf blower which requires a 40:1 ratio. You pour 8 fluid ounces of two-stroke oil into your mixing container. How many fluid ounces of gasoline should you add to achieve the correct ratio?
3. Comparing Mixtures: Your friend has two machines.
   • A chainsaw that requires a 32:1 ratio.
   • A weed trimmer that requires a 50:1 ratio.
   He wants to make a 1-gallon (128 fl oz) batch of fuel for each machine. What is the difference in the amount of oil (in fl oz) needed between the chainsaw and the weed trimmer mixtures?
4. Calculating the Difference: You are supposed to make a fuel mixture at a 40:1 ratio using 2 gallons (256 fl oz) of gasoline. By mistake, you add 7 fl oz of oil.
   • a. How much oil should you have added?
   • b. Is your resulting mixture "rich" (too much oil) or "lean" (too little oil)?
   • c. What is the difference between the amount of oil you added and the amount you should have added?

Answer Key

Part 1: English - Answers

1. Vocabulary: (Answers may vary but should be similar to the following)
   • a. Lubrication: The process of applying a substance (like oil) to reduce friction and wear between moving parts.
   • b. Ratio: A relationship that compares the quantities of two or more amounts. In this context, it's the amount of fuel compared to the amount of oil.
   • c. Combustion: The process of burning, which in an engine, is the rapid burning of the fuel-air mixture to create power.
2. Comprehension: Two-stroke engines need oil mixed with the fuel because they do not have a separate, internal oil system to circulate lubrication to the engine's moving parts.
3. Analysis: A "rich" mixture can cause excessive smoke and foul the spark plug (or leave carbon deposits).
4. Critical Thinking: The 40:1 ratio is "richer". It means for every 40 parts of gas, you add 1 part of oil. The 50:1 ratio requires 50 parts of gas for 1 part of oil, meaning the oil is more diluted (less concentrated).

Part 2: Math - Answers

1. Step 1: Find the total fluid ounces of gasoline.
   5 gallons * 128 fl oz/gallon = 640 fl oz of gasoline.
   Step 2: Calculate the amount of oil needed for a 50:1 ratio.
   640 fl oz / 50 = 12.8 fl oz of oil.
2. Step 1: The ratio is 40:1 (Gasoline:Oil). You have the amount of oil.
   Step 2: Multiply the amount of oil by the gasoline part of the ratio.
   8 fl oz of oil * 40 = 320 fl oz of gasoline.
3. Step 1: Calculate the oil needed for the chainsaw (32:1 ratio).
   128 fl oz / 32 = 4 fl oz of oil.
   Step 2: Calculate the oil needed for the weed trimmer (50:1 ratio).
   128 fl oz / 50 = 2.56 fl oz of oil.
   Step 3: Find the difference.
   4 fl oz - 2.56 fl oz = 1.44 fl oz difference.
4. The ratio is 40:1 and you have 2 gallons (256 fl oz) of gasoline.
   • a. Correct amount of oil:
     256 fl oz / 40 = 6.4 fl oz.
   • b. You added 7 fl oz, which is more than the required 6.4 fl oz. The mixture is "rich".
   • c. Difference:
     7 fl oz (what you added) - 6.4 fl oz (what you should have added) = 0.6 fl oz.