* Radiator: A common point of failure. Look closely at the radiator for any cracks, especially at the seams or where the plastic tanks meet the core. Also check the radiator hoses where they connect to the radiator for leaks or looseness.
* Water Pump: A failing water pump seal can leak coolant, especially when the pump is under pressure from the running engine. You might see a leak around the pump itself.
* Hoses: Check all coolant hoses for cracks, bulges, or leaks. Pay particular attention to the upper and lower radiator hoses, heater hoses, and any bypass hoses. Look for wet spots or discoloration.
* Thermostat Housing: The gasket on the thermostat housing can fail, allowing coolant to leak.
* Head Gasket: This is a more serious problem. A leaking head gasket can allow coolant to mix with the engine oil (creating a milky substance in the oil) or to leak externally, often appearing as a leak near the engine block. This is less likely if the leak is small and only noticeable after driving.
* Coolant Reservoir: Cracks or a faulty cap can cause leaks from the overflow reservoir.
* Pressure Cap: A faulty radiator pressure cap won't maintain proper system pressure, potentially leading to leaks from other, weaker points in the system.
How to Diagnose:
1. Visual Inspection: Start with a thorough visual inspection of the entire cooling system when the engine is cool. Look for obvious signs of leaks, wet spots, or white residue (dried coolant).
2. Pressure Test: A pressure test of the cooling system is crucial. A mechanic can perform this test, pressurizing the system to reveal even small leaks.
3. Inspect Coolant: Check the coolant level in the reservoir. Also, check your engine oil for milky discoloration (indicating head gasket failure).
Important Note: A small leak can quickly become a major problem. Ignoring a coolant leak can lead to overheating, engine damage, and potentially a costly repair. It's best to get your 1998 DeVille checked by a mechanic as soon as possible to pinpoint the leak and prevent further damage.
