That’s why we need an overflow tank to cover the air space created during contraction.

When the fluid cools the engine down, it contracts thus, air pockets appear. It can be caused by rust in the cooling system due to the air flowing into the radiator. Once you do this, the oxidation can cause brown rust to the metal parts, thus, causing a lack of fluid flowing and damaging the engine. One of the common mistakes that some people make is adding water to the reservoir. It’s important to fill the radiator with the proper fluid. Why is my antifreeze brown? Improper radiator’s liquid is one of the reasons. If something goes wrong in the system, there will be a high chance of antifreeze mixing with the transmission liquid. In auto transmission cars, the engine cooling system also works to ensure the coolness of the transmission. This contamination is caused by a damaged cylinder or faulty head gasket. When the coolant looks brown, it can be the consequence of oil mixed in the antifreeze. If you ignore the issue, you need to invest more money in repairs. When the antifreeze can’t function well as a protector, the brown sludge or slime sets in, and the whole cooling system and flow to the engine are blocked, leading to leaking or overheating the engine. Since the radiator is made of metal, and the antifreeze can degrade, the chemical reaction between the two elements creates some reddish deposits. CorrosionĬorrosion is the most common reason for antifreeze brown. It’s not recommended to mix two incompatible reservoir liquids otherwise, the mix of antifreeze will make the additives “drop out” and cause brown radiator fluid. Meanwhile, the additives are responsible for preventing scaling, cavitation, and corrosion. The base of propylene glycol or ethylene glycol is supposed to freeze and protect the engine from overboiling. Why is my coolant brownish? Coolant includes a base, additives, and water. So, what are the reasons for the brownish antifreeze? Addictives Dropping Out No matter the reason, you should remove as many contaminants as possible and offer your car the correct fluid.

Brown coolant in reservoir can be the result of contamination, corrosion, or the air getting into the radiator.

Sludge in radiator overflow tank