6v-92 thermostats

Should be 170s. What temps are you reading with IR at the thermostat housing tops?
Assuming TA's.
As we have repeated, slow down to save fuel, open them up from time to time to clean the slobber out.
Fuel coolers usually cool the fuel before tank return.

I'm thinking the cooler your referring to is the air charge after cooler heat exchanger. It probably does cool fuel.
Some engine coolant is diverted to it and cools it again with the first flow of cool raw water. This now, real cool coolant is then pushed thru a air cooler (after cooler) under the blower, cooling the air charge rite before it's blown into the lungs. Cool air is more dense, more O2. The flash may be hotter and more complete.
After cooling down the air charge after the turbo and blower, the return coolant can be pretty warm. The engine coolant then rejoins the motors circulation before the main heat exchanger.
The engine thermostats does not control the temperature of the after cooler.
If your motors are not coming up to thermostat opening temperature (your notes 160) during operation, you may be replacing them anyway.
Those IR guns sure are handy vs trusting old remote gauges.
You probably will never see your thermostats open up at dock side.

I got a lil long winded here not to preach to you, but to ensure were on the same page and help others under stand.
I also would like to hear from anybody that has experimented with different thermostat specs.

BTW; The 12V71TAs and TIs we work on (including our TIs) use 170 degree thermostats. Their making HP for a while before all four of the thermostats are wide open.
It is interesting our loaded temperature is 180 on all, at speed.

Same topic,
On my 6-71s the t-stats open at 170 , what is the temperature we should expect them to close again?
When I run at speed they open as requested however when I drop down to 900rpm the temp drops to 120° and stays there causing them to run cold.
To me they should close again allowing my engine to stay closer to 160°.
Also if I just stay at 900rpm from initial start the engines run at a nice 160 which I think is pretty good.
This comes into play because I speed up to "clean out the slobber"

Thanks, this is why I think my stats are buggered. One is worse than the other.

Raw-sea water temps and cooling design have a lot to do with block temps.
My 12s cool off to around 150-160* when not running hard.

I would agree with you however no matter what the seawater Temp is the stat should not allow the engine to drop down to 120° within 5 minutes of coming off plane.

The stats very well may be closed at 120*. There are by-passes that keep coolant ALWAYS moving.
These by-passes and a H/D heat exchanger probably can cool the motor off to 120*.

Again would agree but the starboard engine cools to 25° cooler than the port. So I keep coming back to the stat.

Are there different temp ranges for these stats?

I have 4 stats per engine. When we rebuilt the stb main 15+ years ago, new stats went into both engines.
All fresh 170s.
The further up the St Johns river, we find more cool spring water.
Just at a fast idle, say 1000 to 1100 RPM, south of Astor, I don't think our 12s read over 120*.
I had to clear some grass from our thru hulls once, super quick time under the water, darn cold and gators about.