Coolant Pump Temp

Need to ask a few questions;

The 180 & 181 temps are from gauges or IR gun?
6-71 naturals? No Turbo?
Original DDC or Covington or SS or ST or other marinizer?
4 or 6 port water manifold from the head to the thermostat?
Both engines have the same 4 or 6 port water manifold?
Both engines have the same heat exchanger?
Both engines have the same engine oil cooler?

New issue or never measured these temps before?

With a Turbo, more questions; Wet or dry turbo (water cooled or warped in foil)?
Inter cooler (air cooler between the turbo and blower)?
Thermostat on the back of the water manifold facing back or comes up behind and into the H/E?
Horse power tune if known.
Original marinizer or original paint color (green, white, beige)?
Oceans used DDC, Covington and S&S mostly. Others were used on occasion.

Sorry for the 20 question drill. Lots of many marine packages on the 6-71 block.
We need to ensure were talking about the same package to be of any help.

Then 475hp is what the engine is tuned for. This tells us you also have a high out put engine with by-pass blower.

The 6-71 starts life as a plain industrial long block. Ready for the final bolt on options for use in trucks, pumps, tractors, generators, PTO and boats.
Including DDC (Detroit Diesel Corp), there were many other different companies that purchased these engines and bolted on their own marine options. They all had their own heat exchangers, oil coolers and lots of different water tubes, hoses, pumps and thermostat housings.

Sometimes these companies had their own engine paint color, Covington used beige.

Is that the pan-cake engine? Laid over like an ole slant-6 and not straight up.
Uses different plumbing, heat exchangers and maybe different thermostat housings, also.

Have have a fair idea of what you have now. I'll start looking thru my notes. Get back to you with some ideas later.

Starting here first;
Same coolant and mixture (50/50 or 60/40) in use for both engines?

Is this at idle dockside or underway in gear, making horse power?
In just a few moments from running to idling down, crawling down into the engine room and shooting the fresh water pump with an IR gun, H E (heat exchanger) water temps can change drastically.
That pump (fresh/circulating) is drawing water from 2 different paths. The H E and the thermostat bypass.
On the outside, the pump is near the same from 50 years ago.
Do you have any notes on your engines past history? Thru the years, there was 4 (or more) ridged impellers in that DDC water pump. Currently 2 different impellers in my notes.
Any fresh water pump service history? Different impellers here may cause different readings here, between engines.
Any IR readings from the H E?

This may, but usually not a good indicator dock side.
At idle, the beam level of so little can make the out water look greatly different.
At speed, may be a better indicator.
If at speed. please tell us more about this.

Thru the years, we have found many external issues that would contribute to warm engines or real raw water restrictions.
The butt bitters were;
Barnacles in the thru hull, before, in & after the sea-cock.
Also the inlet to the strainer basket.

Collapsing raw water supply hose. internal Delamination in the raw water supply hose.
The suction of the raw water pump draws (sucks) the hose in like a paper straw.

Raw water pump zincs falling into the system restricting raw water flow at or past the pump.

And my favorite (again last spring on another boat), old zinc chunks restricting the raw dump water after the H E and in the exhaust dump cans (shower heads, exhaust-water mixer, exhaust riser).

Like checking fuel system issues, a lil vacuum/pressure gauge can be a great tool.
With adapters, screw one in at the many zinc locations. Make a log of pressure readings at various RPM on both engines.
Could be interesting results. This can be done dockside.

Keep us up on your adventures.

Coolant venting.
I am sure any trapped air has long ago worked out.

I assume your coolant recovery system is working fine including fresh 7lb pressure caps (part number 6410879).

Just in case ya wanna know;
There are a couple of air trap locations on this monster.
Those lil hoses in the picture should vent the turbo and back of the exhaust manifold and fixes the big air trap issues.
The last air trap may be at the thermostat housing.

Crack this plug to vent the housing.

The picture in post #6 made it look like a Pan-Cake install.
DDC did this to lower the install height for some customers.

You have the Real Macoy, DDC 485 HP, 6-71 TIB.
Sweet.

Should also be 2 plugs on your raw water pump that may use zincs.

You pulled this screw??

485 HP tune was DDC.