* Head Gasket Failure: This is a very common cause of overheating and water leaks (but not necessarily coolant leaks). A blown head gasket allows combustion gases to enter the cooling system, pressurizing it and forcing water out. This often leads to a milky or brownish residue in the engine oil (check the dipstick). Pressure testing the cooling system is essential to diagnose this.
* Cracked Cylinder Head or Engine Block: A crack in either component would allow coolant (or water, if it's low on coolant) to leak out. This is less likely if it's only leaking water, but still a possibility, especially if the engine has high mileage. Again, pressure testing is crucial.
* Radiator Leak (Not just the hoses): Inspect the radiator itself closely for any cracks, pinholes, or leaks, especially at the seams. A slow leak may only manifest under pressure.
* Water Pump Leak: While less common if it's only leaking water, a failing water pump seal could leak. However, usually this leads to coolant loss, not just water.
* Radiator Cap: A faulty radiator cap may not hold pressure correctly, causing the coolant to boil over and leak. This is a cheap and easy part to replace first.
* Cooling System Pressure Relief Valve (part of radiator cap): This can sometimes malfunction and not release pressure properly, leading to leaks. This is a part within the radiator cap.
Troubleshooting Steps:
1. Pressure Test the Cooling System: This is the most important step. A mechanic uses a pressure tester to pressurize the cooling system and look for leaks. This will pinpoint the source of the leak much more effectively than visual inspection.
2. Inspect the Radiator and Hoses Thoroughly: Look for any visible cracks, bulges, or soft spots. Check the hose clamps for tightness.
3. Check the Engine Oil: Look for milky or brownish discoloration, a sign of coolant mixing with the oil (head gasket failure).
4. Replace the Radiator Cap (Cheap and Easy First Step): It's inexpensive and might be the solution.
5. Consider the Water Pump: If all else fails, the water pump could be at fault, though it's less likely if it's purely a water leak.
Important Note: Driving a car with an overheating engine can cause serious and expensive damage. Do not continue to drive the Lumina until the problem is diagnosed and fixed. Have it towed to a mechanic if necessary. The longer you drive it while overheating, the more likely it is to cause irreparable damage to the engine.
