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Monsoon 409 Thermostat Location


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KnoxTNBoats

I have a 2015 Malibu Wakesetter 23 LSV with the Monsoon 409 engine. I have around 800 hours and I’m looking to replace the thermostat. Can anyone show me a picture of where the thermostat is located? I pulled the plastic cover expecting it to be visible from the top, but I’m not seeing where the thermostat would be. Thanks!

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KnoxTNBoats

Yes, issue with high temp when idling after I take off trailer - temp rises at idle until I give it 2k plus rpm’s, then it’s fine for the day. I always trailer, so not sure what would happen if I left it in water until cool down completely. New impeller this season - old impeller looked fine.

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KnoxTNBoats

I have had it for a year. Had no issues for 3 months, then toward the end of the season started to see this issue.

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Have you changed your impeller recently?  If no, you should.  Also check for debris/blockage in the water strainer.  Verify there is no water leaking from the raw water pump and all hose clamp are snug tight on all water cooling hoses.

Sorry, just saw you noted that you changed impellers.  Did you also replace the gasket/o-ring?  Sounds like you have an issue with poor suction or air getting into the raw water circulation lines.

Edited by BuFootin
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If the engine is only overheating at idle, then you should check the air purge fitting and hose first.  There is a small through hull fitting just above the port exhaust flapper on the exterior transom of the boat.  There should be a stream of water coming out of it when the engine is running.  The through hull fitting, bleed hose, or the metal bleed line on the top of the engine may be clogged.  Reverse cooling systems on the GM Gen IV engines require that air bleed hose to cool properly and the small lines and fitting are easily clogged when they use raw sea water for cooling.

Edited by csleaver
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  • 11 months later...

Hey @KnoxTNBoats follow Csleaver recommendation, I have the exact same motor and year and had the exact same problem, Csleaver nailed it. I had a small amount of rust buildup inside the small metal crossover tube (it's what the air breather tube goes into and crosses over to the other side of the engine). It's very easy to remove it and inspect. once I cleaned out the rust out everything operated as normal.  I wouldn't have figured it out without Csleaver. 

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Posted (edited)

Yep same issue I had.  This will sometime cause O2/emissions codes because leaks in the systems bleeds fresh air into the post cat sensor causing the ecu  to think there’s unburnt O2 in the system where it shouldn’t be. 

Edited by PNWoke
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  • 1 month later...

Hello,  I have a 2019 MLX with the 409 Monsoon.   The boat is throwing a SPN:441 FMI:15 code.  I swapped the Manifold temp sensors with no Luck.  Checked strainer and all hoses.  Any ideas if it could be the small breather tube or?  Appreciate the help.  Thanks 

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A worn or faulty impeller is the most common cause of exhaust overheat codes.  Worn sensor connection plug sockets can cause faults.  On the PCM Challenger 409 Monsoon, I have seen excessive buildup of corrosion or sediment clogging up the manifold cooling passages cause them to overheat..

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Thanks Csleaver.  Which side is the SPN:441?  I was told port.  Replaced the impeller and still throws the same SPN:441 code.  Also, how do you clean and flush the Manifolds and what can you do about worn sensor connection plug sockets?  Plan to replace the temperature sensors this week.  

Really appreciate the help.  Trying to do what I can before a 6 hour round trip to the dealer.  Thanks 

Edited by MalibuHawk
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SPN 441 refers to the bank1, which is the starboard side in a v-drive boat with a GM engine.  Take off the exhaust manifold water hoses and remove the threaded casting plug on the lower cooling passage to inspect for blockages.  I've used CLR to clean them out, but sometimes replacement is required depending on the condition. 

Damaged sensor connector contacts can be bent back into shape or replaced as needed.

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Thanks for the Information.  The dealer told me port, not surprising.  I took out the impeller, strainer, and all drain plugs and ran water through both manifolds today.  I’ll take out the casting plug and use CLR and see what I find tomorrow. Do you run the boat on a fake lake after you pour in the CLR or just flush with CLR with the casting plug out?  Really anppreciate all the help.  

Edited by MalibuHawk
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Hey Csleaver, I have a question for you if you are still checking in.  I can only get the boat to throw a code when we are driving.  Not at the dock or on a fake lake at the same RPM.  Does that add anything to the diagnosis?  I’m concerned the dealer won’t be able to replicate.  

Thanks for the help. 

Edited by MalibuHawk
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Without further inspection it is all still speculation.  Note the speed, RPM, weight, conditions, and amount of time operating the boat when the alarm occurs.  With accurate notes, I expect the dealer could replicate the problem on the water.

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Thanks Csleaver,  Really appreciate the help.  I pulled out the casting plug and both holes were plugged with some sort of flakey clay like debris.  Flushed engine and will test on Thursday.  I currently working to find the Catanium Exhaust Manifold part numbers, as a back up.  Thanks again.  

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Quick Update.  Pulled both casting plugs, flushed the manifolds 3 times, checked strainer, changed both Temp Sensors, O2 Sensors, Impeller and ran on fake lake for 30 minutes.  Drop in water last night for an hour at the same speed and setup as when the boat previously threw a 441 code.  Boat ran great and never threw a code.  We are going to run all weekend and see what happens.  It looks like the exhaust manifold flush will be part of our annual routine, I’m guessing that was the problem.  

Csleaver- Really appreciate all the help.  

One last question?  Would it damage anything if I mix CLR & water and leave in the Exhaust Manifold only for 24 hours and then flush?  

Thanks Again.  

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Appreciate the response. After driving the boat for 2 hours today, the 441 code came back.  I am guessing we are at replacing the manifold.  

A bummer for sure.  I found one on Palmerpower.com.  Anybody have experience with them?  

Thanks again. 

Edited by MalibuHawk
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