Yes they will help.
One of your problems is the ECM thinks the engine is running cold. It is up to you to determine if it is.
This can be done a few different ways.
Could use a IR temp gun to check actual temp to what ECM thinks it is.
Ohm meter to compare resistance of sensor to the table that's in the service manual.
Unplugging sensor while diacom is running to see what temp ECM shows, Should read -22°F. Then jumper the 2 connectors and see that it reads 266°F.
The #7742218 manual walks you thru all the tests.
But my guess is still a bad thermostat or it's possible that the oring that holds it in place has come out of position.
Summer to winter temp shouldn't change that much. You need to track down why it does. Lake temp of 55° shouldn't have any effect.
A rule of thumb.
Running hot at idle that goes away with increased RPM usually points to a old impeller that has taken a "set".
A air leak on the suction side usually causes hot running that gets worse with increased RPM's.
Notice I said "usually" because there are other factors that can come into play.
When you pull the thermostat housing to check the thermostat. It is best practice to wire wheel the area that the thermostat sits in and where the oring fits. Also look in where the hose from the circulating pump connects. You should see a small passage about 1/2 way in. Run a coat hanger or some mechanics wire thru this passage to make sure it isn't blocked by impeller pieces. This is a very common problem with this design.
One thing that would have made this easier, would be to have done a compete scan of the engine. When you do the next scan, here is my recommendation on how to do the recording.
Start with a cold engine and the boat in the water.
1. connect Diacom
2. Turn on batt switch, turn on key switch -- but don't start engine
3. start Diacom recording -- let run for 30 seconds to one minute
4. start engine
5. check that Diacom is still recording, it's not uncommon for it to have lost communication during starting. If it did, save that recording and start another one.
6. run the boat gently at idle to 1500 RPM until up to operating temp
7. run the boat up to full speed --- take your time, looking to get data here so advance the throttle slowly (spend one to two minutes) now slow back down to minimum wake and idle in neutral for awhile. Use the trim as you normally would.
8. Do a "ski start" -- full throttle all the way to full speed and trimmed out, now back to idle fairly quickly.
9. drive boat back to the dock/ramp and shut off
10. stop recording and name the file
One other thing I noticed when reviewing your file. When graphing I see the battery voltage fluctuating a bit more than normal. This can point to a diode in the alternator going bad or a loose connection. Would be a good idea to do a "ripple test". To do this have the engine running about 1500 RPM and test the AC voltage at the battery, should see less then 0.25 volts AC.
Also, when it comes to testing vs replacement of parts like the thermostat and temp sensor. I highly recommend testing them. I have gotten too many bad parts brand new in the box that are bad to ever trust replacement as a troubleshooting tool.
AllDodge has the correct part number in post #20 for your ECM temp sender. Volvo parts descriptions can sometimes be unusual.
I see nothing unusual in your engine run times. They look very common.
....I know I know... brain fart