[Toughship]

Wondering what troubleshooting steps to take regarding high temp alarm for starboard engine .  New transmission oil cooler was installed , transmission fluid good color and at full level.   Can operate under 10 miles per hour all day without the temp alarm going off, only when increasing speed does the alarm go off , slow down and it stops 
    Starboard engine runs at 180 degrees vs port at 160.  Don’t like the color of the closed cooling system.
Considering flushing the engine closed cooling system and changing the transmission fluid.
   Boat was recently purchased and marine engine survey was done but this problem did not occur during sea trial.
Might even be something simple like a temp alarm sending unit.

[Sans Peur]

You dont say what engines you have but, get an IR gun and see what the temps are comparatively on each engine. It should be easy to find any hot spots. Especially look around the heat exchangers. They may have not been maintained and need cleaning.
Another easy check is water flow. Could need an impeller on one side (but do both, they most likely have the same amount of hours). Start them.up.and see if the hot engine flows about the same as the other side.

[Toughship]

Engines are Crusaders 7.4 , both raw water impellers just changed , pretty good flow out of the exhausts 
    Closed cooling system
I will take IR comparisons to establish a base line of differences between the two engines 
    Something new yesterday , Signs of Muskrat starting to move into the exhaust port opening.
Pulled out grass and dirt , ran engine and back to normal flow .   Now how to prevent another visit ?

[Medicone]

Some people have put a mesh insert/grate into the opening if i recall.  Large enough to allow flow, but small enough to prevent unwanted visitors.

If still running hot, I would also check sea-strainers, hoses from seacocks to sea strainers and heat exchangers for debris - fairly easy to do.

[reeltimebrad]

Since you say the coolant looks suspect you should probably do a pressure check on the closed cooling system, if it checks out good it may be time for a flush and fill.

[Toughship]

Good news, turns out to be a faulty sensor
Great flow entire thru entire cooling system.

Regarding muskrat intrusion, while at the dock I insert 2 mesh screens that are normally used in gutter downspouts . When boat is pulled for the season I may install permanent screens or stainless plates of some type . First time in 35 years at this marina that we had this problem.

[Toughship]

Well back to the service Dept tomorrow, had the high temp transmission warning again so it wasn’t a faulty temp sensor .

[Toughship]

Status :    My technician had a conversation with Velvet Drive and the consensus is that the new aftermarket oil cooler is the culprit.    A factory Crusader oil cooleR has internal baffles to make sure the transmission oil has time going thru the cooler to actually cool down .    Reportedly the after market does not have the internal baffling and therefore the oil flows to fast to actually cool down. 
               Could this be true ?     I plan on tracking down the part number of newly installed cooler and try to learn if it does or does not have internal baffles.