2015 Monsoon 409 Thermostat problems?

[endostrat]

22 VLX which has a 409 Monsoon with 400 hours.  The last couple of times out, the temperature initially spikes around 200 degrees and then it goes down to its normal operating temperature of around 160 for the rest of the day.  I am assuming this is a thermostat issue?  If yes, where is it located and is it a straightforward repair?  

Thanks in advance,

Ryan 

[justgary]

8 hours ago, endostrat said:

22 VLX which has a 409 Monsoon with 400 hours.  The last couple of times out, the temperature initially spikes around 200 degrees and then it goes down to its normal operating temperature of around 160 for the rest of the day.  I am assuming this is a thermostat issue?  If yes, where is it located and is it a straightforward repair?  

Thanks in advance,

Ryan 

I would assume an impeller problem, a blockage, or an intake hose sucking air before I changed the thermostat.  Does it do it if you rev the engine right after you crank it (to help prime the pump)?

To answer your question, the thermostat should be at the top center aft of your engine under a small cast iron cover.  It should be where the cooling hoses split out to go to the manifolds.

[hunter77ah]

9 hours ago, endostrat said:

22 VLX which has a 409 Monsoon with 400 hours.  The last couple of times out, the temperature initially spikes around 200 degrees and then it goes down to its normal operating temperature of around 160 for the rest of the day.  I am assuming this is a thermostat issue?  If yes, where is it located and is it a straightforward repair?  

Thanks in advance,

Ryan 

Prime it like @justgary suggested.  A few blips to 1500-2000 RPM will get it primed.  If this doesn't work, then I would start pulling hoses, etc.  We do this with ours and haven't had any problems.

[teamerickson]

I think @Fman had this issue also?

[csleaver]

There is a small external cylinder head steam vent just above the port exhaust flapper on the transom that purges air from the cooling system on standard/sea water cooled L96/6.0L/409 Indmar engines.  If this is blocked, you can experience overheating at idle.

[Fman]

On 8/24/2020 at 9:19 PM, endostrat said:

22 VLX which has a 409 Monsoon with 400 hours.  The last couple of times out, the temperature initially spikes around 200 degrees and then it goes down to its normal operating temperature of around 160 for the rest of the day.  I am assuming this is a thermostat issue?  If yes, where is it located and is it a straightforward repair?  

Thanks in advance,

Ryan 

I also had this issue with my 2015 22VLX/Monsoon 409.  It would only happen when idling out of 5 mph for a prolonged period of time upon initial launch.  There are a few items I would check.  As others mentioned make sure you have water peeing out that little small port on the transom when engine is running.  If you have a heater make sure the circ pump is functioning properly, that needs to be working to circulate water.  Check your thermostat to make sure it is opening and closing properly.  It is easy to pull out and replace/check.

There were two items on mine that took care of the problem.  The first was when I launched the boat I would rev up engine to 2500-3000 RPMs for a short period of time to burp the system and get any air out of it.  I also drilled a few extra small holes in the thermostat housing to help circulate water before the thermostat opened.  The 409 uses a reverse cooling system, this problem you are experiencing is not uncommon with this engine.  Once the system is purged/burped it will be fine until you take it out of the water again.  It is a great engine but for some reason the reverse cooling system requires some extra attention at launch.

Hope this helps....