Here's why and what to check:
* Heater Core: The heater core is a small radiator located inside the car's dashboard. When the heater is on, coolant flows through it to warm the air. A leak in the heater core will only manifest when the heater is activated. This is the most likely culprit. Unfortunately, replacing a heater core is a significant job, often requiring partial dashboard disassembly.
* Heater Core Hoses: The hoses connecting the heater core to the engine's cooling system can crack, become brittle, or develop leaks, especially where they connect to the core or the engine. Inspect these hoses carefully for cracks, bulges, or loose clamps.
* Heater Core Connections: The connections where the hoses attach to the heater core are prone to leaks due to corrosion or damage to the seals.
* Water Valve (Heater Control Valve): This valve controls the flow of coolant to the heater core. A faulty valve might leak or allow excessive pressure to build up in the system when the heater is on.
Troubleshooting Steps:
1. Visual Inspection: Carefully examine all the hoses and connections associated with the heater core. Look for wet spots, stains, or evidence of coolant leakage. You may need a flashlight and possibly even a mirror to see everything. Pay particular attention to the area under the dashboard where the heater core is located.
2. Pressure Test: A pressure test of the cooling system can help pinpoint the leak. This involves pressurizing the system with a special tool and observing for pressure drops indicating a leak. A mechanic can usually perform this test.
3. Dye Test: Adding a dye to the coolant can help locate leaks that are difficult to see. The dye will glow under a special UV light, making it easier to identify the leak source.
4. Professional Help: If you're not comfortable working on the cooling system yourself, take your Buick to a mechanic. Replacing a heater core is a complex repair.
Important Note: Coolant is toxic, so wear appropriate safety gear (gloves and eye protection) when inspecting or working on your cooling system.
Because you've already replaced the water pump, the heater core and its associated components are the most logical remaining suspects for your leak. A professional inspection is highly recommended to avoid further damage.
