* Coolant Leak: The most likely culprit is a coolant leak. Low coolant levels cause overheating, and the engine may rev high as a safety mechanism (to prevent seizing) or because the computer is compensating for a lack of power due to overheating. Check your coolant reservoir – is it empty or very low? Look for visible leaks under the car (look for greenish or rusty puddles). A leak in the radiator, hoses, water pump, or head gasket are all possibilities.
* Thermostat Stuck Closed: A stuck-closed thermostat prevents coolant from circulating properly, leading to overheating. The high revs could again be a safety or compensatory response.
* Faulty Water Pump: A malfunctioning water pump fails to circulate coolant efficiently, resulting in overheating. This would often present alongside a coolant leak.
* Faulty Radiator Fan: The radiator fan might not be turning on when the engine gets hot, leading to overheating. You might hear a clicking sound from the fan relay when the engine is hot.
* Head Gasket Failure: A blown head gasket is a serious issue. It can cause coolant to leak into the cylinders or oil, leading to overheating and potentially white smoke from the exhaust. It can also cause the engine to run rough and rev unusually high. This is a very costly repair.
* Transmission Problem (Less Likely): While less likely to cause the overheating directly, a transmission problem *could* cause high revs. However, this would likely be accompanied by other transmission symptoms (slipping, hard shifting, etc.).
What to do IMMEDIATELY:
1. Pull over to a safe location immediately. Driving with an overheating engine can cause catastrophic damage.
2. Turn off the engine. Do not continue driving.
3. Let the engine cool down completely. This could take a significant amount of time (hours). Do NOT open the radiator cap until the engine is completely cool, to avoid serious burns.
4. Check the coolant level in the reservoir. If it's low, DO NOT add coolant until you've identified and addressed the leak. Adding coolant to a leaking system will just cause more coolant loss.
After the engine cools:
1. Visually inspect the engine compartment for obvious leaks.
2. Carefully check the radiator hoses for cracks or bulges.
3. Have the vehicle towed to a mechanic. Diagnosing the exact cause requires professional tools and expertise. Ignoring the problem will only lead to more expensive repairs in the future.
This situation is a serious one requiring immediate professional attention. Don't attempt to diagnose or fix this yourself without proper knowledge and equipment.
