What effects can high fuel temperature have on engine performance?

High fuel temperature can significantly impact engine performance by causing vapor lock and reducing fuel density. Vapor lock occurs when the fuel evaporates in the fuel lines or the fuel system due to excessive heat, resulting in bubbles forming in the fuel. This can interrupt fuel flow to the engine, leading to misfires, stalling, or reduced power output.

In addition to vapor lock, increased fuel temperature lowers the density of the fuel. When the density of the fuel decreases, there is less mass of fuel being delivered to the engine for combustion, which can lead to a lean fuel mixture. A lean mixture can cause an increase in engine operating temperatures and may also result in knocking or pinging, ultimately harming engine performance and efficiency.

In contrast, the other options suggest either beneficial effects or a lack of significance regarding high fuel temperatures, which are not accurate representations of the negative impact that high temperatures can have on fuel and, consequently, engine performance.