If you open the radiator cap or lift up the cap on the coolant reservoir and find oil mixed in with the coolant system, it means your Ford Focus has a leaking head gasket, damaged cylinder block or a cracked cylinder head.
The damage to the engine could have resulted from a motor that overheated or if the vehicle was in a car accident. It is not uncommon for a car accident to crack the engine block.
Running the car without any coolant or water could have caused the engine to overheat. If you don’t add oil to the engine, and the oil level is too low, it will cause the engine to overheat.
If you don’t perform routine oil changes, the oil will break down and cause engine components to heat up, warp and wear out. The motor will run hot and damage a head gasket, crack a cylinder head or engine block.
The coolant flows through pathways in the engine block and cylinder head. If the engine block or cylinder head cracks, oil will work its way into the coolant passages. If the head gasket is damaged oil can leak into coolant passages.
Can you drive your Ford Focus with oil in the coolant?
Absolutely not. If oil is in the coolant it will lead to catastrophic engine damage. The engine will overheat and the block will seize, moving mechanical parts will heat up, bend and break. It could result in a fire or small explosion of parts being ejected from the engine.
If a lot of oil is in the coolant it will appear like brown sludge at the top of the radiator and in the coolant reservoir.
How expensive it it to replace a head gasket?
A local repair shop will charge you roughly $900 to $1,200 to fix a blown head gasket on your Ford Focus. Anything more than that and you are being overcharged.
A dealership might charge anywhere between $1,600 to $2,500, depending on which engine you have. The dealership might even charge you to rebuild the cylinder head, or at the very least, resurface it.
Other symptoms of oil in the coolant
If oil is in the coolant, the vehicle might also have white smoke coming from the tailpipe. You might notice bubbling in the radiator or coolant reservoir, milky white coloration in the engine oil and an overheating engine.
A cylinder head crack or leaking head gasket often have the same symptoms. You might notice a drop in engine performance or lowered cylinder compression pressure.
You can perform a cylinder compression test or leak-down test. These test will determine the overall condition of the engine and in most cases pinpoint the source of the problem.
Ford Focus Service Manual, (2015). ‘Diagnosis and Testing’, 6/26