Overheating Issue

How is your coolant level? Coolant still clean?
How do you know it's over heating?

Do you have a coolant recovery bottle?
This is a 6-71TIB, rite?

Next time you run, see if bubbles are coming up thru your coolant recovery bottle.

Is it still your e gauge that states your getting hot?
With I R gun, what is real temp middle of expansion tank?

Where is home? Close?

I'm concerned it may be a leaking injector tube. Combustion gases leaking into the cooling system.

Do you have the correct coolant mix ? Is the coolant greater than 50/50 ? If so you will more than likely run warm .

Check the smaller coolers. I had an issue like this and it ended up being zincs in the fuel cooler, which was directly after the raw water pump. Those are easy to pull hoses off of and shine a flash light through.

No, raw water sides. Clutch and fuel coolers. Maybe even the dump can mixer. Any where old zincs and debris can collect and restrict water flow.
I now remember a problem I had 15 years ago and will return to again soon. The dump can mixers on out Berts 12V71 were full of old zincs and debris.

Still watch that coolant getting darker. Learned a good lesson last year on one customers boat and an other customer going thru it again now, leaking injector tubes.
Some old school shops may still have test strips that detect expanded gases in the coolant. Get some of these.

Dump can mixer;
Where the raw water after the engine HE, fuel cooler, clutch cooler connects with the exhaust system to cool the hot expanding exhaust gases.
Usually a series of holes in the dump can (riser) pouring the used raw water into the exhaust.
That first rubber exhaust hose connects to this dump can.

Injector tube.
Not complicated, just hard for me to explain but I'll try.
Think of it as a copper sock that is installed in the cylinder head, thru the closed water system.
It is flared and crimped to make it's ends seal in the head. The fuel injector is installed snugly in this sock (injector tube).
The engine coolant helps keep the injector temp constant helping it match the performance of all the other injectors and keep the injector cool also.

The tip and crimp of this sock on the cylinder end does take some abuse.
After some injector changes and / or improper or inconsistent torquing of the injector retainer may cause it to leak.
It usually shows it's symptom at speed when cylinder pressures start really getting up there.
This problem luvs to show up in TAs and TIBs because of the added cylinder pressures at speed.

Now you have a small amount of air in the system. All cooling designs do not allow air in the system. Some items may get hot.
First easy detect is a small stream of bubbles in the recovery bottle. Next symptom is dirty coolant.

I hope I explained that well, Anybody else is welcome to give it a try.

I'm in for kidney surgery tomorrow noon. Their going fishing for some stones,, again..
I'm pretty hosed up on Vicodin now. Only took me 30 minutes to type that. Glad it helped.