Coolant Pump Temp

Mine are only 410's but do have a zinc off of a plug on the inboard side of the raw water pump as well as the trans oil cooler, the fuel oil cooler and the HE.

My J & T engines are the 485 hp 6-71 TIB I have the original spec sheets and J & T manuals.

Don't forget to make up and bring some pressure gauges to plug into what zinc ports you do have.
I did find a collapsed in a supply hose years ago this way. Pump made little pressure, made a heck of a vacuum on the pump low side when it was revved up.

Coolant pump ? What do you mean?
Raw water pump or closed cooling pump ?

RichV
You got some things to check out . One at a time, Process of elimination.

1- make sure you have full water flow at your engine water intake , hull screen strainer, clamshell strainer, seacock and whatever up into the water pump including the hose.
2- Remove and check your heat exchanger, clean it and inspect and clean the HE tank.
3- pull all inlet hoses , water flowing into the various oil coolers, make sure they are clean and clear. Old zincs and junk will collect on the perforated screen strainers within the coolers cause blockages.
4- remove intercooler , get it cleaned.seams to me it clogged up.
5- check raw water impeller, check the pump it’s self for blockages , old impeller veins get jammed up in the pump causing restrictions.
6-remove the exhaust hose at the mixing elbow, remove the entire elbow if you can. Make sure all the little water holes in the elbow are open and clear.
7- inspect the exhaust muffler you mentioned, for blockages. Yup high heat can mess them up. Critters can to. Muskrats and what not can get up in there and cause damage and problems.
8- make sure the rubber hose and fitting / 90 that dumps sea water into the exhaust elbow is clear.

Yup it’s a bit of work , but one thing at a time. You will find your sea water blockages. Collectively they can all add up to one big problem. Lack of water at the exhaust outlet. And hot engine temps.

Just to make sure, your label of port / stb is bass ackwards ??

Ah, but there's da rub ,,
These are no hot engine temps. The systems are working.
Just interesting on point readings.

This could be interesting; Air not getting cooled as well as other engine. Reinforcing lack of green water flow thru it.

There is a by-pass line around the inter-cooler in the event it gets clogged.
How well this smaller by-pass line passes green water could be a mystery.
Yes, good maintenance is to check the inter-cooler inlet from time to time (air and water passages).

After the inter-cooler (we put the pressure gauge in the zinc hole on the trans cooler) did not test these options.
If there is no water pressure after the raw pump, before any options, Then all this may be moot.
Then time for a vacuum gauge on the raw pump inlet.

DDC fuel (& clutch) coolers were usually straight tube type coolers. No restriction there. Interesting this is after the inter-cooler.

As I typed in post #9, measuring water flow by eyeball, dockside at idle, is hard to do.
Any way to get a look at speed?

I was not going to go there yet, because your readings at the temp senders were darn good.
Save that for last, then replace both of them (each engine).

Question, same coolant in both engines?
Same exact ratio?
50/50 or 60/40?
I wonder if different rations could result in some different spot readings.

We run with more water than glycol down here.
It is the water that transfers the heat.
The glycol keeps things from freezing, rusting and lubricated.
In FL, we rather transfer heat than worry about freezing.

Get that water flowing out the rear orifice like the cool running engine. Then mess with the thermostat if need be.
More coolers , exhaust elbow , intercooler, and stuff to get to yet. More debris to find. You’ll get it ….
FYI, just saying my J and T 471s do not have a bypass line on the intercooler. Are you sure you have one ?

In my PDF and his picture, there is a intercooler bypass.

Are you sure you don't have one?

I am not 4-71 heavy but 6, v8 & V12s I work on have one.
My 12V71TIs use the IC bypass as a fuel cooler path.

Harris intercooler , water in one side , out the other. That’s all I’ve got. Remember mine sits right on the back just above the clutch. Low pro file. I don’t have room for any other hoses and lines ! Lol.

I think that was one of the trade offs in marinizers. Covington's and J-T's may not have used IC bypass lines.

I'm thinking back on that 6-71 TIB Covington I used to manage... Nope, no IC bypass there...
With all it's tubes, hoses and a wet turbo the size of a VW Bug;; Proof that the DDC 6-71 could make some dependable (500+) HP and just smile back.
A V-71 can not do that.