What Causes the Red Color on Spark Plugs?

Understanding the Red Color on Spark Plugs

By analyzing the condition of a spark plug, mechanics and automotive enthusiasts can gain valuable insights into the health of the engine and its performance. One particular phenomenon that often raises questions is the appearance of a red color on spark plugs or reddish tint on the spark plug tips. This article delves into what causes this red color, its implications, and what you should do if you notice it on your spark plugs.

Red-tipped spark plugs

Causes of Red Coloration on Spark Plug Tips

The red color on spark plug tips is usually a sign of the presence of metallic additives or fuel-related contaminants. Here are the most common causes:

• Fuel Additives: One of the primary causes of red coloration on spark plug tips is the use of fuel additives that contain metallic compounds. These additives are often included in octane booster products to enhance performance, improve fuel economy, or clean the engine.
• Manganese-Based Additives: The most common additive that causes a red tint on spark plugs is MMT (methylcyclopentadienyl manganese tricarbonyl), a manganese-based compound used to increase the octane rating of gasoline. MMT can leave a reddish-orange deposit on the spark plug tip, particularly on the insulator and electrodes.

Effects on The Engine

While MMT can help improve octane levels and reduce knocking, its residues can accumulate on the spark plugs over time. These deposits are typically harmless in small amounts but can indicate excessive use of fuel additives or lower-quality fuel.

Octane booster causes a red color on spark plug electrodes and insulator discoloration

If a fuel additive contains an iron component, it can cause red deposits on the insulator nose, center electrode, and side electrode. The iron coating is electrically conductive and can cause misfiring.

Source: Bosch

The iron coating is Ferrocene; “an organometallic compound with the formula Fe(C 5H 5) 2. The molecule is a complex consisting of two cyclopentadienyl rings bound to a central iron atom. It is an orange solid with a camphor-like odor that sublimes above room temperature and is soluble in most organic solvents.”

Iron oxides from fuel system corrosion is also a cause of a red spark plug electrode

Source: Underhood Service

The fuel filter and fuel pump sock will prevent solid rust particles from entering the combustion chamber, but they can’t prevent soluble iron oxide from entering the combustion chamber. During combustion, the iron oxides deposit on the spark plug insulator, center and side electrodes.

©, 2022 Rick Muscoplat