If your car with high mileage gradually loss power while driving on any road conditions, but the car top speed remains the same as it was.
Car Problem Diagnosis
A high mileage car with gradual lack of power on all road conditions, flat road or uphill, is and indication that the car has weak compression. Compression is when the air/fuel mixture is squeeze inside the car combustion chambers. A car of a higher compression is an indication of a more powerful engine, however as the engine continuously operates its components worn out. If these components become worn it can cause a weak compression on the engine. Parts that can cause a weak compression if worn out are valves, rings, and timing belt. A worn timing belt can slip just enough to cause the engine timing to be off, thus can cause a weal compression.
Possible Cause of Loss of Power
All about car Recommendation
Bring your car to a reputable auto repair shop to check for the weak engine compression. If the mechanic confirms that the engine has a weak compression, the first thing to look up to is the timing belt. Ask the mechanic to check the timing belt for wear and replace it if necessary. If the timing belt is found to be in good condition, the next part to check is the valve of the rings, either of the two is the cause of the weak compression. In any case please be preferred to shoulder all the cost because this kind of repair can cost you a lot.