Monsoon 409 Thermostat Location

[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!

[granddaddy55]

are you having cooling problems?  if not leave alone

[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.

[hunter77ah]

Is it new to you? With the 409 you have to purge the air. 

[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.

[BuFootin]

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 May 12, 2023 by BuFootin

[csleaver]

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 May 12, 2023 by csleaver

[Rednucleus]

Does not sound like a thermostat problem - follow suggestions listed above!

[2011vlx]

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. 

[PNWoke]

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 May 8 by PNWoke