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Old 04-01-2020, 18:56   #1
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Join Date: Nov 2019
Location: Australia
Boat: mainship 34 trawler 2005 Twin
Posts: 4
Yanmar 4LHA-STP Sea water passage service question

Hi, Happy New Year to every one!

Last year I bought a Mainship 2005 trawler with twin Yanmar 4LHA_STP engines which only recorded 300 hours. I have been driving it for 150 hours since May 2019. The engines run perfectly and temperature range at 75 degrees below 3000 RPM and at 84 degree at 3400 PRM, and also I checked the impellers in good condition and the water flow very normal. One of my experienced marine mechanic reminds me that the engines need to do sea water service since the record shows the impeller pump hasn’t been serviced since Feb-2011. But according to the manual, it only needs to check or replace the impeller at 1000 hours or 4 years and clear and check the sea water passage at every 2000 hours. So my question is –do I need to check and clean raw water pump, inter cooler, oil cooler , after cooler and all the sea water passage now? I used to have Yanmar 6LAPA, its manual says the sea water passage needs to be checked 1250 hours or every 5 years. Thus my other question is why 4LHA-STP only need to clear the sea water passage at 2000 hours but the 5 years? Does this mean 4LHA is a better built machine?The last question is what exactly mean in the manual “to clear and check sea water passage?” Does it mean I have to dissemble all the coolers and heat exchanges to check and clean them ? Thank you very much!
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Old 05-01-2020, 04:30   #2
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Join Date: Feb 2010
Posts: 618
Re: Yanmar 4LHA-STP Sea water passage service question

Hi mainship 34
I disagree with Yanmar regarding the raw water pump impeller, the rubber blades would be permanently set where the cam contacts them if the engine was rarely or never used (one of the problems with keeping a spare pump on board with the impeller in place) and its simply not worth taking a chance that the impeller might be ok for 4 years with a high output engine like yours.
The raw water system on your engine does need to be cleaned and maintained , maybe more than most small marine engines due to the complicated route the seawater takes through the heat exchanger and coolers. I suspect that 4LHA series engines have a higher raw water system pressure or rather that most small yacht engines have almost no system pressure so never blow raw water cooling hoses ...... which seems to happen sometimes to 4LHAs. A mechanic here is doing a system flush thing with “Barnacle Buster” or similar de scaling product with some success and it sure beats the hell out of removing the exchanger and cooler end caps to get to the cores.
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