Mercruiser 8.1 Guardian mode

Hello everyone,
New to the forum.
I have twin 8.1 Mercruiser V-drive, closed cooling inboards in a 2008 Searay 340 Sundancer. Boating is in saltwater.
The STBD engine after warm up goes into Guardian mode when throttled above idle speed. The readout on the Smartcraft is overheat condition, check water inlet, check sea water pump. Also the continuous alarm sounds sometimes an hour after the engine is shut down, very strange!
I changed the Seawater pump and impeller, the temp sensor, and thermostat.
All suggestions appreciated and thanks in advance.

Thanks so much for the response and I should have included additional troubleshooting information.
Yes, I checked temps all over the engine with a thermo gun and all is normal as compared to the Port engine.
I did recently check the heat exchanger and all is good. I did not backfluch the system being that all the temps are in order. The gauge also reads 170 for temp.

Yes I'm going to swap the water pressure sensors that I think are mounted on the seawater pump. The boat is a 2008 but I have owned it for only 3.5 years.
Thanks again for staying with me!
No, the risers are not original but were replaced 4 years ago. I flush the boat every time I run it.

Thankyou for the response!
I tested all thr hoses, bolts, clamps on the engines, basically went nuts with the temp gun!
We operate the boat in salt water, the lowest depth being 8' but water is pretty clean.
Great suggestion feeling the hoses as we ramp up speed. I will try that this Thursday.
Last night I took the end caps off of the heat exchanger and cleaned the tubes with pressurized water, compressed air and a coat hanger. From what I could see, they were not that clogged.
I also pulled off one exhaust elbow and it looked good.

No the risers are not new, they were replaced about 4 years ago by the previous owner.
The boat is a 2008 model.
Thanks for your response.

Great suggestion on. the heat exchanger, I did open it up last night, shot it with pressurized water and air. Ran a coat hanger through each tube and it seemed clean.

After trying many troubleshooting tips, I am Still at ground zero. One new discovery is the smartcraft system on the troubled engine shows 9.9 volts when shut down and every other gauge including the batteries shows 13.2 volts.
The troubled engine consistently goes into guardian mode indicating overheat as the problem but nothing is hot. The alarm will even go off two hours after the engine is shutdown?
Any help is really appreciated.

Tried your suggestions and temps are good on everything that should be warm.
After trying many troubleshooting tips, I am Still at ground zero. One new discovery is the smartcraft system on the troubled engine shows 9.9 volts when shut down and every other gauge including the batteries shows 13.2 volts.
The troubled engine consistently goes into guardian mode indicating overheat as the problem but nothing is hot. The alarm will even go off two hours after the engine is shutdown?
Any help is really appreciated.

Thankyou for the reply,
I actually just changed the alternator two days ago because it seized up. New alternator indicates on the smartcraft 14 volts of charging when running. The batteries are fully charged as well. Still checking electrical connections and reading wiring diagrams.
I do have a mechanic who will plug in the diagnostic terminal and praying this shows something.
Almost ready to swap the control module?

Yes I did swap the sensors with no change. Yes the low voltage is a big concern being that my batteries read 13.4 volts.

I changed the alternator again and that fixed the voltage problem. Back up to 12.5v on the helm gage.
Changed the seawater pump again and no change, the alarm Still sounds when warm and put in gear.
Any suggestions really appreciated.

I changed the alternator again and that fixed the voltage problem. Back up to 12.5v on the helm gage.
Changed the seawater pump again and no change, the alarm Still sounds when warm and put in gear.
Any suggestions really appreciated.