How does fuel consumption behave when engine coolant is boiling?

[GeorgeFitz]

Fuel consumption will increase when the engine coolant is boiling. Correctly adjust tire inflation pressure: Maintaining proper tire pressure can reduce rolling resistance and lower fuel consumption. Additionally, a slightly higher tire pressure (e.g., +0.2bar above the recommended value) can also save fuel. Moderate use of in-vehicle auxiliary electrical equipment: Using certain electrical devices can significantly increase fuel consumption, such as the air conditioning system's cooling function. Once heating purposes are achieved, seat heaters should be turned off promptly. Similarly, rear window defrosters should be turned off when there's no fogging or icing. Proper gear usage: Match gear selection with appropriate vehicle speeds - avoid high-speed low-gear or low-speed high-gear driving. Shift gears in advance, ensuring the selected gear matches the speed range. Never drive at high speeds in low gears or at low speeds in high gears.

[ChristianDella]

When the engine coolant boils, fuel consumption usually increases significantly. I've driven many cars and encountered similar situations. Once the water temperature rises to the boiling point, the engine overheats and struggles to operate, directly reducing combustion efficiency. The fuel pump has to work harder to supply fuel, but the power output is compromised, wasting gasoline in vain. Driving like this for a long time can increase fuel consumption by 10% to 20%, and it can easily damage internal engine components or even cause cylinder scoring, leading to costly repairs. This mainly stems from cooling system issues, such as a leaking radiator, a non-functioning fan, or a stuck thermostat failing to dissipate heat in time, causing the car to overheat. It is recommended to pull over immediately, turn off the engine, check the coolant level, and seek repairs if necessary. Developing a habit of regular maintenance, such as checking the water temperature and antifreeze level monthly, can help avoid such troubles.

[Stewart]

Coolant boiling often leads to increased fuel consumption because an overheated engine experiences greater internal friction, causing cylinders to malfunction and combustion to become inefficient. More fuel is burned but not converted into useful power, instead turning into waste heat that's expelled, wasting fuel. I often see car enthusiasts on forums complaining about similar situations—ranging from just a few liters higher fuel consumption to severe cases requiring major repairs or even posing safety hazards, such as smoke or breakdowns. This issue may also stem from poor heat dissipation, such as a clogged radiator, a faulty water pump, or high ambient temperatures with poor ventilation. Early intervention is key: first, stop the car to let the engine cool down, then replenish with purified water or antifreeze—avoid using tap water directly as it contains impurities that can harm the engine. During daily driving, avoid sudden acceleration or heavy loads, as these can exacerbate overheating.

[SanDaniela]

Engine coolant boiling will definitely lead to increased fuel consumption. When the engine operates at high temperatures, the system automatically increases fuel supply in an attempt to cool down, but this results in low efficiency—consuming more fuel while producing less output. Common causes include insufficient coolant, fan failure, or aging and leaking hoses. I once experienced this on the highway, and it scared me so much that I immediately pulled into a service area to add water, which stabilized the fuel consumption. Ignoring it not only causes a sharp rise in fuel consumption and a rapid drop in the fuel gauge but may also damage sensors or lead to costly cylinder overhauls. For prevention, I check the cooling system monthly and replace the antifreeze during maintenance to ensure the pipes are sealed—effectively avoiding such troubles, saving fuel and money.