It is essential to determine whether the engine coolant is mixing with engine oil or automatic transmission fluid, as both systems rely on coolant for temperature regulation. PHOTO | WWW.VWVORTEX.COM
Hello Paul, my Mercedes C200 engine coolant fluid in the plastic reservoir has developed a milky brown colour. During a service, my mechanic observed this and suggested it might indicate oil mixing with coolant. What could be the cause, how can it be fixed, and will it damage the engine? Bosco
Hello Bosco, when engine coolant mixes with oil, it often turns milky brown. It is essential to determine whether the engine coolant is mixing with engine oil or automatic transmission fluid (gearbox oil), as both systems rely on coolant for temperature regulation. Contamination in either can lead to severe damage if not addressed promptly.
To diagnose the issue, a sample of the engine oil or gearbox oil should be examined using a dipstick or by draining a small amount of fluid. If there are traces of coolant contamination, evident as a milky brown colour, this will confirm which system is affected. This diagnostic process requires an experienced and well-equipped mechanic.
If the contamination is found in the engine oil, the most likely cause is a failure in the engine oil cooler. This component contains chambers that allow coolant to flow and cool the engine oil by conduction. Over time, delaying coolant renewal can cause the coolant to become corrosive, which may perforate these chambers. This allows oil and coolant to mix.
A close examination of the oil cooler will reveal any leaks, and it should be replaced if necessary. After replacing the cooler, the engine oil, oil filter, and coolant fluid need to be serviced or replaced to restore proper functioning.
In rare cases, especially if the car has experienced overheating episodes, the cylinder head gasket may be damaged. This can also allow oil and coolant to mix. Your mechanic should inspect the cylinder head gasket for signs of failure and carry out repairs if needed.
If the contamination is in the automatic transmission fluid, the likely culprit is the gearbox oil cooler, which is integrated into the radiator.
Corrosion caused by delayed radiator coolant renewal can damage the plates that separate the coolant and transmission fluid. When this happens, coolant can mix with the transmission fluid, leading to contamination.
To resolve this, the radiator should be replaced, the cooling system flushed, and the coolant reservoir cleaned. Fresh coolant should then be replenished. Additionally, the gearbox will require servicing, including replacing the transmission oil filter and renewing the automatic transmission fluid (ATF).
It is crucial to address this issue immediately, as prolonged contamination of oil or coolant can cause significant damage to the engine or transmission. Ensure that regular maintenance, including timely coolant renewal, is performed to prevent similar issues in the future.
