Lot 2624: 1966 Pontiac GTO

Based on my research, here are the most common engine problems with the 1966 Pontiac GTO’s 389 V8:

1. Nylon Timing Gear Failure - This is the big one! The factory used nylon-coated timing gears that would flake off around 30,000-40,000 miles. When this happens, the nylon pieces clog the oil pump pickup, causing sudden oil starvation that can seize the engine or destroy bearings. It’s catastrophic when it fails.

2. Overheating Issues - The 389 runs hot by nature, especially with the Tri-Power setup. Common causes include inadequate cooling systems, blocked radiator passages, or timing that’s too advanced. Many owners upgrade to aluminum radiators (like the one in this listing) to help.

3. Oil Pressure Problems - The 389 can have poor upper-end oiling, with rockers not getting enough oil. This is often due to restricted oil passages or worn oil pumps. The engine in this listing has been rebuilt, which should address this.

4. Detonation/Pinging - With the high compression (10.75:1 on Tri-Power models), these engines are prone to detonation under load, especially with today’s lower-octane fuel.

5. Tri-Power Specific Issues - The three two-barrel carb setup can have fuel percolation problems after shutdown, causing hard starting when hot.

The good news is that this particular GTO has a rebuilt engine with an upgraded aluminum radiator, so the previous owner likely addressed the timing gear and cooling issues. When considering any ‘66 GTO, always ask if the timing gear has been replaced with a steel one - it’s essential preventive maintenance.

Would you like me to help you find similar GTOs or answer any other questions about this classic muscle car?