Automobile Repair/Honda/Civic/Radiator Flush and Fill
According to the service manual, the 1992-1995 Civic engine has a drain plug for the coolant system on the side of the block, in addition to the drain at the bottom of the radiator; it is approximately in the center of the front side of the engine, beneath the exhaust manifold. This plug is extremely tightly seated, has a very shallow head, and direct access is blocked; making it almost impossible to remove, even with an appropriately sized 6 point socket (if it is successfully removed, the head is usually severely rounded off in the process, thus it is advisable to have a new replacement on hand before the job is begun).
In practice, therefore, very few mechanics (even in dealer service areas) attempt to open this drain during a coolant replacement, relying instead on the radiator drain and flushing the old coolant out with water. In fact, many dealer service mechanics and part departments do not even know of the existence of this block drain until it is shown to them in the manual. However, since the block cannot be completely drained without removal of the plug, and since Honda coolant is sold pre-diluted and ready for use rather than in concentrated form, there remains the choice of diluting the new coolant with the water remaining in the block, or wasting some expensive coolant flushing the remnants of the water out of the block. Most mechanics who have attempted to remove the plug from the block, however, will choose one of these two alternatives in future.