Low temp

[rakr]

I have a 2004 LSV Monsoon 340. Boat the last 100 hours or so has always stayed at 160 while warmed up. This morning took the kids skiing and it never went above 140. Battery is good, other gauges work fine. Manifolds do feel cooler. Ran at 160 yesterday. 
 

what are the odds the thermostat is stuck open? Currently pulling it out and sticking it in some hot water to test. Any other ideas? 

Is it bad to run it at a lower temp? 

of course I have a spare at home about 2 hours away… 

Thanks! 
 

Edit. (not pulling the thermostat, I don’t have any gasket sealant.) I’m assuming I can just pull the blue plug to see if water is flowing with lower temp to see if water is flowing before the engine is up to temp, correct? 
 

thanks!!!

 

 

 

Edited July 4, 2023 by rakr

[rakr]

I don’t think the blue plug is what I want…
 

To make sure my understanding is correct. Raw water intake to impeller, impeller to “bottom” side of the thermostat housing. Under 160 the water only goes out to the exhaust manifolds (and right past the blue plugs), but does not go through to the other side of the “bottom” housing. It only passes through to the other side at/above 160. 
 

correct? 
 

checking that now. 
 

edit. At 140 degrees, lots of water out of the other side of the thermostat housing. 

Edited July 4, 2023 by rakr

[justgary]

My impression of the shape of the two castings from my 1999 Monsoon is the following:

1.  Raw water enters the lower casting through the right port (looking at the front of the engine), where it splits into two streams.  First stream goes out the left port to the J-hose and circulation pump into the block.  Second stream diverts to the upper casting, where it mixes with water above the thermostat (which lives between the castings) and leaves out the left and right ports to the exhaust manifolds.

2.  Water in the block circulates through until it gets to the lower casting, where it splits into two streams.  First stream goes out the left port to the J-hose for another lap through the block.  Second stream goes through the thermostat only if it is open, where it mixes with raw water from second stream (above, in #1) and exits the left and right ports to the exhaust manifolds.

It looks like water that is in the block will stay in the block and circulate until the thermostat opens.  After that, it will exit to the exhaust manifolds and get replaced with new water from the raw water pump.  In other words, the only way the block can stay too cool is if the thermostat is stuck open or rusted through (if it is a steel version).

I don't see where you have much choice but to pull the thermostat for inspection and testing.  A tube of goop to reseal it is available and cheap at any auto parts store (or even Wally World).

[UWSkier]

21 hours ago, justgary said:

My impression of the shape of the two castings from my 1999 Monsoon is the following:

1.  Raw water enters the lower casting through the right port (looking at the front of the engine), where it splits into two streams.  First stream goes out the left port to the J-hose and circulation pump into the block.  Second stream diverts to the upper casting, where it mixes with water above the thermostat (which lives between the castings) and leaves out the left and right ports to the exhaust manifolds.

2.  Water in the block circulates through until it gets to the lower casting, where it splits into two streams.  First stream goes out the left port to the J-hose for another lap through the block.  Second stream goes through the thermostat only if it is open, where it mixes with raw water from second stream (above, in #1) and exits the left and right ports to the exhaust manifolds.

It looks like water that is in the block will stay in the block and circulate until the thermostat opens.  After that, it will exit to the exhaust manifolds and get replaced with new water from the raw water pump.  In other words, the only way the block can stay too cool is if the thermostat is stuck open or rusted through (if it is a steel version).

I don't see where you have much choice but to pull the thermostat for inspection and testing.  A tube of goop to reseal it is available and cheap at any auto parts store (or even Wally World).

Or better yet, get some gasket paper from Amazon or Wally for 4 bucks and make a new gasket. Saves you the time of waiting for the RTV to set up. 

[rakr]

Cork and rubber was the ticket. I’ll probably replace at some point? Thermostat was definitely bad. I didn’t really understand the principle behind the RTV. Backwoods auto parts guy said “just slop it on there and make sure to get around the screws.

I tried 2 different kinds of paper gaskets and they leaked, some more than others. 
 

I’ll probably replace with the gaskets from skidim next time I’m at the cottage.