Modern engines rely on cooling liquid, or coolant, to keep them running at the correct temperature. While operating at normal cruising speed, the average engine produces 4,000 controlled explosions a minute, ignited by the spark plugs. These explosions produce heat, and the coolant takes the heat away from the engine. Coolant circulates through passages inside of the engine, near the combustion chamber where these explosions take place, as well as in other areas where extreme friction creates heat. The coolant then passes through a radiator, where it exchanges that built-up heat with air. The water pump is critical to the process, as it forces the coolant through the engine.
One of the most common failures of a Civic water pump is that it begins leaking coolant. These leaks start as a slight seepage but can soon grow to the point of a major leak, requiring you to add coolant often. Water pumps leak around the sealsand the impeller shaft, as those parts wear out. Unless it is just the gasket leaking, you must replace the water pump to repair the leak.
Water pump noises are difficult to diagnose, because it is difficult to isolate the noise to the water pump. Use an automotive stethoscope to listen, placing the probe on the water pump if it is accessible. If not, placing the stethoscope on the timing belt cover may allow you to hear the noise, but it can also show other noises not related to the water pump.
When you can't see any other cause for overheating, you must consider the water pump as the possible culprit. When the water pump becomes weak, it cannot circulate the engine coolant with enough efficiency to dissipate engine heat. The coolant does not flow through the passageways quickly enough, so it gathers too much heat, leading to overheating. This is difficult to diagnose, so you must evaluate it considering the mileage of the vehicle. Evaluate any other possible causes of overheating first.
On many vehicles, particularly the '95 Honda Civic, the water pump is run by the timing belt. Timing belts must be replaced at certain mileage intervals. Many times, because the labor has already been paid for the timing belt and the water pump would add little in labor dollars to that job, it makes sense to replace the water pump as a preventive measure. You will never be any closer.
