* Distributor Cap and Rotor: Heat can cause cracking or arcing in the distributor cap and rotor, leading to a loss of spark. This is a very common issue in older cars. Inspect for cracks, burns, or excessive wear.
* Ignition Coil: The ignition coil can weaken with age and heat. It might produce enough spark when cold, but not enough when hot. A failing coil will often struggle to create the necessary high voltage for ignition under heat.
* Fuel Pump Relay: The fuel pump relay could be failing due to heat. The relay might work intermittently, or only when the engine is cool.
* Fuel Pump: While less likely to be solely heat-related, a failing fuel pump might struggle to deliver sufficient fuel pressure when hot due to decreased efficiency from heat.
* Mass Airflow Sensor (MAF Sensor): While less common in a '85 Mustang (which likely has a carburetor, not fuel injection), a malfunctioning MAF sensor (if equipped) could provide inaccurate readings when hot affecting the air/fuel mixture.
* Engine Coolant Temperature (ECT) Sensor: This sensor influences the fuel mixture. If faulty and sending incorrect readings when hot, it can affect starting. This is more applicable if you have fuel injection (unlikely for 1985, but possible depending on modifications).
* Worn Starter Motor: Although less likely to be *specifically* a hot-start problem, an overheated starter motor might struggle to engage. This is more likely to manifest as slow cranking or no cranking, rather than a complete no-start.
* Wiring Issues: Heat can cause wires to short or their insulation to degrade, leading to poor electrical connections. Inspect all wiring, particularly around the distributor and ignition coil.
Troubleshooting Steps:
1. Check for Spark: With the engine hot, have someone crank the engine while you check for spark at the distributor cap. If there's no spark, the problem lies in the ignition system.
2. Check Fuel Pressure: If you have a fuel pressure gauge, check the fuel pressure when the engine is hot. Low pressure indicates a problem with the fuel pump or its related components.
3. Inspect the Distributor Cap and Rotor: Visually inspect these for cracks, burns, or excessive wear. Replacement is relatively inexpensive.
4. Listen for the Fuel Pump: When you turn the key to the "on" position (but don't crank), you should hear the fuel pump briefly run. If you don't hear it, check the fuel pump relay.
If you are not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic. Improperly diagnosing and repairing electrical issues can lead to further damage. Always disconnect the negative battery terminal before working on any car's electrical system.
