Guardian Alarm at 3K RPM, Exhaust Steam, Possible Overheat

We are looking for opinions and feedback fromknowledgeable marine gas engine mechanics, etc.

We have a 2002 Bayliner with two Mercruiser 350 MAG MPI Horizons gas inboards. We have only owned the boat for 8 months, and have very little knowledge of the engine maintenance, other than the port side block has been replaced 09/2018 and the starboard side block replaced 07/2017. (Blocks replaced due to water backwash.) We understand that there are less than 30 hours on both blocks. This is what we know:

PORT SIDE

• Block replaced 09/2018 (25 HOURS)
• Exhaust manifold. riser, elbows replaced 09/2018
• All other components such as heat exchanger is original 2002 equipment (we have not proof or verification of any replacement or servicing)
• Steam from exhaust
• Engine running temp 175-178 degrees
• IR Temp at exhaust elbows: 95-98 degrees

STARBOARD SIDE

• Block replaced 07/2017 (35 HOURS)
• Unknown condition of exhaust manifold, or if/when replaced at time of last block replacement
• All other components such as heat exchanger is original 2002 equipment (we have not proof or verification of any replacement or servicing)
• Mass steam from exhaust
• POSSIBLE side causing Guardian Alarm at 3K RPM
• Engine running temp at 178 degrees
• IR Temp at exhaust elbow: 98 and 101 degrees

We have replaced the impellers, the metal housings looked okay with no grooves.

We get a guardian alarm at 3,000 RPM, with temps approaching 180 degrees.

There is an abundance (vast amounts) of steam from both exhausts, more on the starboard side.

OUR PLAN

• Remove and service, or replace heat exchangers.We believe the zincs in the heat exchangers may not have been replaced inseveral years.
  
• Service or replace Oil Coolers and TransmissionCoolers
  
• Disassemble and examine Starboard exhaustmanifold
  
• Install 6" risers on both engines forbetter exhaust hose slope
  
• Install inline exhaust flappers (Corsa flappers)

ANY THOUGHTS OR INPUT???

Your feedback is welcomed, as we are novices atthis.

Why not get both engine ECUs scanned before through a small fortune of new parts into it?

For less than one heat exchanger costs new, you could get a pretty capable system from RINDA....

Thanks for the feedback. We had a Mercruiser mechanic scan ECMs, and he made a suggestion that included items/plan above. However, he wasn’t definitive in his assessment of the problem; thus the inquiry of a second opinion here.

Why not share what the ECM scans revealed?