Love this one ! Took me a while to get the idea, so I can pass this along. The cooling system is not just based on the elbows and impellers. As mentioned water flow volume makes a big difference. Imagine trying to cool an iron used to press clothing by spraying water on it from a spray bottle. All it is going to do is cool to "X" level and turn some of that water to steam. If you were to flood it constantly with larger volumes of water, the likelihood of you substantially cooling the iron becomes greater and the steam effect is minimal.
Add that thought to the 3 elements of a fresh water ( assumed) cooled engine. Pumping thru the transmissions, the u-coolers and the heat exchangers all add to the potential flow reduction for the water to remove heat.
I have changed parts and pieces all over the place when I first was dealing with this kind of issue years back but it wasn't until I had a better grasp on the mechanics of the system that I have run for years, never having a cooling problem. Once certain days we do get a bit of steam but I am willing to believe it is more atmospheric conditions than cooling that becomes the root cause. At one point the steam trails were over 20 foot long and temps around 180...too much