Expert: Everett Peacock - 9/21/2011

Question
1989 Bayliner I/O.  Originally had a 5.0, but sometime in the past somebody put a 7.5(460) in this boat.  Problem is that i can't figure out why the exhaust hoses keep melting.  Upon first inspection I noticed that hoses off the riser were only rated at 180 deg F.  I thought that was the problem as the exhaust gets hotter then that, so I changed them.  Put marine exhaust hose on, rated at 350 deg F.  Took it to the lake the following weekend and it melted.  Checked for restrictions in the outdrive.  Nothing restricting the flow of exhaust and water.  Checked the impellar.  Looked perfect.  Put a new exhaust riser on and new hose. Thought the exhaust riser had become so old and corroded(rusted) that it was restrictiong the flow of water into the exhaust.  afer about 30 mminutes on the lake(again) the hose melted.  Water is flowing through the exhaust riser on the lake as it steams from the water hitting the hot exhaust.  I also checked it prior to putting it in the water, and water is flowing freely.  Temp on the gauge is reading a bit over 170 deg.  I didnt trust it so i put a laser temp on the engine.  It is correct.  What to do now.???????? It is always the Left side hose(if driving the boat) that is melting.  No problems from the right side.  Themastat seems to be working.  Engine does have another water pump on the block, but water is flowing.?? Any suggestions would be appreciated.!!

Answer
Did you just buy the boat ???     If you did and it was like this from the beginning, then my suggestion is to install a thru hull fitting with a sea water pump to eliminate the pump in the gearcase....Sounds like there is a lack of cooling water....and I have found in the past that on older models the water passage in the drive and transom assy get retricted for corroision .. from age...