* Blown Head Gasket: This is the most common cause. A failing head gasket allows coolant to leak into the oil. You'll likely see milky, mayonnaise-like residue on the oil dipstick or filler cap. This is a significant repair requiring head gasket replacement.
* Cracked Cylinder Head: A crack in the cylinder head can also allow coolant to mix with the oil. This is often accompanied by other symptoms like overheating, loss of coolant, or white smoke from the exhaust. Repair usually involves head replacement or extensive repair.
* Cracked Engine Block: Less common than a cracked head, a crack in the engine block can also lead to coolant entering the oil. This is a very serious and expensive repair, potentially requiring engine replacement.
* Leaking Oil Cooler: The oil cooler, if equipped, can fail and allow coolant to leak into the oil system. This is less common but still a possibility.
* Improper Coolant/Oil Mixture: Though less likely, someone may have accidentally added coolant to the oil.
What to do immediately:
1. Stop driving the vehicle immediately. Continuing to drive with water in the oil can cause catastrophic engine damage.
2. Have the vehicle towed to a qualified mechanic. Diagnosis requires a professional inspection to pinpoint the source of the leak. Do not attempt to continue driving or repair it yourself.
3. Do not add any more oil. Adding oil might mask the problem and cause further damage.
Ignoring water in the oil will almost certainly lead to a costly engine rebuild or replacement. Prompt professional attention is crucial.
