* Fuel System Heat Soak: The fuel in the carburetor (if carbureted) or fuel lines can heat up significantly after prolonged running. This can lead to vapor lock, where the fuel vaporizes instead of staying liquid, causing fuel starvation and a power loss. This is more likely in hot weather.
* Ignition System Heat Soak: Similar to the fuel system, components like the coil, distributor, and wiring can overheat and malfunction. This can lead to weak or intermittent sparks, resulting in misfires and power loss.
* Cooling System Issues: While not directly causing a power loss at 30 minutes *precisely*, an inefficient cooling system might cause the engine to overheat gradually. Overheating can lead to numerous problems, including detonation (pre-ignition), loss of compression, and damage to vital engine components, all manifesting as power loss. This is a serious issue and should be addressed immediately. Check your coolant level, radiator, thermostat, water pump, and fan.
* Carburetion Issues (if applicable): If you have a carburetor, issues like a faulty accelerator pump, clogged jets, or a worn-out float can cause fuel delivery problems that worsen as the engine heats up.
* Exhaust System Restriction: A severely clogged exhaust system can restrict exhaust flow and cause excessive back pressure. This can lead to overheating and reduced power.
* Valve Train Issues: While less likely to be precisely time-related, worn valve lifters or rocker arms might be affected by heat, leading to inconsistent valve operation and power loss.
* Fuel Pump Issues: A failing fuel pump might be able to keep up at lower temperatures but struggle once the engine and fuel heat up.
Troubleshooting Steps:
1. Check your coolant temperature: Does the engine overheat after 30 minutes? This is a crucial first step.
2. Inspect the fuel system: Look for signs of leaks, check fuel pressure, and ensure the fuel lines are properly routed and not exposed to excessive heat.
3. Check the ignition system: Inspect the coil, wires, distributor cap and rotor for cracks, burns, or other damage. Consider testing the ignition components.
4. Examine the carburetor (if applicable): If your engine has a carburetor, it might need cleaning, rebuilding, or replacement.
5. Inspect the exhaust system: Check for any blockages or restrictions.
6. Listen for unusual noises: Any knocking, ticking, or other unusual sounds could point to a mechanical issue.
Safety First: Overheating can cause serious engine damage. If you suspect overheating, stop driving immediately and allow the engine to cool before attempting any further diagnosis.
It's difficult to diagnose this remotely. The best course of action is to have a qualified mechanic inspect your Chevy big-block to pinpoint the exact cause of the power loss. Providing more information, like the year and model of your Chevy, engine specifics (e.g., 454, 427), and any other symptoms you've noticed, could help narrow down the possibilities.
