Cross Systems 2016
Hot item  Hot exhaust risers can indicate a serious problem.   While the engine exhaust riser temperature can vary between  manufacturers and old versus new  risers,  the temperature should not exceed a temperature that is warm to the touch. If you can not hold your hand on the riser, it is too hot. In the absence of a portable thermometer, the surveyor should be able to touch the riser without pain or injury. Even if the the engine temperature gauge indicates a normal temperature  the riser may be poor condition.   If the risers cooling water passages are constricted, note photo below, sufficient water  will not pass through to properly cool the remainder of the exhaust system.  In many  systems the next link is rubber which will burn when sufficient cooling water is restricted.  Once the rubber portion burns two things are  likely to occur;   1. Sea water will enter the hull. 2. An engine compartment fire will ensue.   The riser pictured below has been in use in salt  water, summers only,  for four seasons.   Viewing the riser from the top (Figure 1),  which is often the only view available, indicates a riser  that is in good condition and free from rust.   Notice the view from the bottom photo,  which indicates the cooling water passages are almost completely blocked.