1. Air in the Cooling System: Even though you refilled the coolant, air pockets can remain trapped, especially after working on the system. These air pockets can interfere with the cooling system's ability to circulate coolant properly, potentially leading to overheating and causing the engine to shut down as a safety precaution (or preventing it from starting at all). This is a likely culprit. Solution: Properly bleed the cooling system. Your Cadillac's repair manual will describe the procedure, but it generally involves running the engine, allowing it to reach operating temperature, and opening bleed valves (if present) to release trapped air.
2. Low Coolant Level (Despite Refilling): You might have a leak somewhere else in the system, even after fixing the hose. Check for leaks around the thermostat housing, water pump, radiator, heater core, and all hose connections. A small leak can still cause problems.
3. Damaged Thermostat: It's possible the new thermostat is faulty. A stuck-closed thermostat prevents coolant flow, leading to overheating. A stuck-open thermostat can cause the engine to run cold and struggle to start, although this is less likely to completely prevent starting.
4. Sensor Issues (Less Likely): The cooling system interacts with various sensors (e.g., coolant temperature sensor). A malfunctioning sensor could send incorrect information to the computer, preventing the engine from starting. This is less likely to be a direct cause of a no-start after hose/thermostat replacement, but it's possible.
5. Coincidental Problem: The work you did might have simply uncovered a pre-existing issue that was unrelated to the cooling system. Consider these possibilities:
* Ignition System: Check the spark plugs, ignition coil, distributor cap, rotor, and ignition wires. A failing component could prevent the engine from firing.
* Fuel System: Ensure you have sufficient fuel, and check the fuel pump, fuel filter, and fuel injectors.
* Crankshaft Position Sensor (CKP): A faulty CKP sensor can prevent starting.
Troubleshooting Steps:
1. Bleed the Cooling System: This is the most likely solution. Do this *before* moving on to anything else.
2. Check Coolant Level: Look for any leaks. Top off the coolant if necessary.
3. Inspect the New Thermostat: Make sure it's installed correctly and functioning as it should. If you have a spare, try swapping it in.
4. Check for Spark: Use an inline spark tester to confirm if you have spark at the spark plugs.
5. Check for Fuel: Check fuel pressure and whether fuel is reaching the injectors.
If you've tried these steps and the car still won't start, consult a mechanic. They have the tools and expertise to diagnose more complex issues. Providing more details about the symptoms (e.g., any unusual sounds, smells, or codes) will help in diagnosing the problem.
