Boat- 2003 40' Ocean Yacht Super Sport
Caterpillar 3126b
Port motor replaced in 2005 - hours 500 (no ideawhy, first owner)
Starboard motor 2003 - hours 700
Engines are electronically monitored.

Ran the boat about 140 miles from Fort Lauderdale to CapeCanaveral at 2140rpms. Speed was 23kn and fuel burn was 33/gphtotal. Upon reducing engine rpm I notice the manifold temp on starboardengine climb to 140* Port motor was at 88*. Next day warmedup the motors for 15-20 minutes and set off at idle speed. Within about10 minutes the screen gave a warning, High manifold temps, reduce powerimmediately. I didnít see the temp because warning message was coveringit.

Back at the dock I removed the sensor on the starboardmotor. The element was full of carbon/soot. I cleaned it with atowel and tried again. Same high temps to 140* but no alarm. Ithen switched the senders and got the same values. Determined sensorswere working. When the temps climbed to 140* I would give a little rpmwithout load and watch the temps come down 10-12* but would rise back to140* at idle.

It was suggested to run the motor with the sensor plugged inbut out of the engine. While doing so I could feel rhythmic puffs of aircoming out of the hole where sensor would go. When engine was turned off,air rushed out. Did the same on port motor but instead of puffing air, Icould feel a slight vacuum pressure and when motor was cut, no air rushedout.

6 months prior, both motors had the after coolers, heatexchangers and turbos serviced and cleaned. Elbows were sent out, boiledand reinstalled. The boat was run for about a total of 20 hours fromSeptember to March. In March a full engine inspection and sea trial weredone. All values checked out including runs at idle, half load, 3/4 and100% and well as monitoring on cool down. Engine and gear oil sampleswere taken and sent out. Both came back all normal. Max RPMachieved under load was 2740, just shy of the 2800 that manufacturesuggests. Bottom was clean as well as shafts and props. Prior ownershowed valid receipts for the service conducted. Other than that I doníthave any other service records.

The fact that air is "puffing out" coupled with acarbon covered sensor probe vs a vacuum and a clean sensor on the port motor maysuggest to me that there is an intake valve seating issue. I am not amechanic or very familiar with diesel engines.Iíve heard everything from a lifter, valves out of adjustment, toneeding a whole new head or new after coolers.The fact that air is pushing out of the sensor port vs sucking in leadsme towards intake valve issues.Anysuggestions Ö. Much appreciated.