Internal leaks are when the fluids enter another circuit and may result in changes to the coolant or oil. The former may be the presence of foam (caused by hydrocarbons) in the coolant expansion tank. Coolant leaking into the oil system may result in a mayonnaise, or milkshake-like, substance in the oil, often to be seen on the dipstick, or oil filler cap.
Internal leaks occur when fluids seep into another circuit, potentially altering the coolant or oil. This may manifest as foam (caused by hydrocarbons) in the coolant expansion tank or coolant leaking into the oil system, resulting in a substance resembling mayonnaise or milkshake on the dipstick or oil filler cap.