The relationship of temp and flow is very simple. If the fresh water does not have the required flow (Basic assumption) then it means it goes SLOWER thru the heat exchanger and therefore spends MORE time in contact with the raw water. It then loose more calories if heat in the slow transition and exits the heat exchanger at a lower temp (i.e. 70 degrees)

The flow problem however is also working in the other side of the fresh water loop. The 70 degree water enters the engine (at the assumed SLOW rate) and there it absorbs much more heat calories and gets to the high temp of 200 degrees. And the loop repeats. (If it flows faster it would not reach 200 and will remove more heat... No alarm ;-)

So the assumption is that if you will provide more flow rate the fresh water will be able to absorb all the needed calories from the engine and the temp will only reach 195 degrees (for example) which in turn is less then the 200 (No high temp alarm) and also able to get down to the same 70 degree output from the heat exchanger. (As there is LESS temp difference between the input temp at 195 and the output temp at 70 the heat exchanger will have less calories to get read off and transfer to the raw water.) Now the system is working as intended to provide proper cooling as result of higher flow. Slow flow is probably pointing at fresh water pump or residue in the fresh water passages of the engine.

Of course the assumption could be incorrect too. Which mean that the flow is right and the problem is then that the fresh water should be at a lower then 70 degrees to provide enough heat removal from engine. Therefore the input temp should be 195 degree and the raw water will cool the fresh water to a lower then 70 degree temp.

In the 2nd case the problem is shifted to the RAW WATER loop and could point to slow flow of the raw water probably pointing at raw water pump or residue in the raw water passages of the engine heat exchanger or residue/block at the water injection point to the exhaust system.

Looks like there are problem in one of the two loops and you need some info from the engine manufacturer (temp, and flow rate at engine RPM) and local troubleshooting.