Raw Water Pressure

[bud37]

Source of the post Typically, what pressure range do crank driven raw water pumps operate in, idle up to wide open throttle? I've been a little under the weather lately and have not worked on my project. So, it gives time to think about some improvements and search the web. I want to add a pressure gauge to my dash so I can keep tabs on what the pump is doing.

Have you considered monitoring the flow instead of pressure......I believe the flow would be a more accurate assessment of cooling performance than pressure. With an open system I just think pressure might not be an accurate representation.There are some out there, Livorsi marine is one....have a look, can't hurt........

[mjk1040]

I'm thinking the raw water pumps are more displacement pumps than pressure pumps? I agree you would like to know the flow not the pressure. Changing just the impellers may not be the only problem with the FW pump. The cams in these pumps wear too, so a new impeller along with new cams may be in order along with checking the wear of the pump housing too?

[Viper]

Pressure's important too. In fact most have moved away from higher volume to higher pressure while keeping sufficient volume in mind. It's natural for things to take the path of least resistance, the less pressure there is the higher the chances are that some critical areas will not see full flow. Pressure also keeps the boiling point up which could be beneficial in a failing cooling system. The drawback is that the higher pressure impeller designs make them less flexible and forgiving, and thus more susceptible to failures. Either form of monitoring will give some picture of what's going on. The more information you have the better as long as it's not distracting enough to interfere with safety.

[tomschauer]

If you start with a known "clean " open system, either pressure or flow monitoring would work. When your system starts to foul, your pressure would rise or your flow would drop. Either way you would be alerted to a potential problem.
On the other side of the coin, if you blew a hose on the outlet of the pump, your flow would greatly increase and your pressure decrease, again you know you have a problem.
I see no reason to go with a high volume or high pressure pump on an everyday application. Either of these would overcome the normal slow rise over time of a cooling system being degredated until it became an emergency and then you are dead in the water, no slow ride to home port. On a racing or high perf application, go for it!

[mjk1040]

As always great info from all!

[bud37]

So here is another for discussion....a regular occurrence is the failure of impeller blades..... a blade or two fail and get lodged in the heat exchanger inlet.....now in this case it is more than possible that the pressure will not be much different than previous between the pump and the restriction , but the one thing that will change will be the flow as it will drop. Now that said ,I believe all these systems are over designed so you would probably not see any change in cooling performance because there would be enough flow thru the exchanger to cool the engine.The reduction might only be evident by flow measurement or visual at exhaust outlets...what do you do with I/O or underwater exits.
So for me , I think in a perfect world you would monitor both flow and pressure,then you would have the best of both worlds to give the ability see performance degradation before it bites ya and a troubleshooting tool.......... ..

[Keith S]

You don't mention what engines you have. But for comparison, Mercruiser engines with Smartcraft can access water pressure readings. The readings I have seen range from 2-3psi at idle up to the mid 20s at WOT.

[dcrahn]

Thanks for all the input guys, loads of good information here. If I can fit it in to my budget, I'll install both. Pressure gauge will be the lowest cost of the two, so that will be added first.

[dcrahn]

Source of the post You don't mention what engines you have. But for comparison, Mercruiser engines with Smartcraft can access water pressure readings. The readings I have seen range from 2-3psi at idle up to the mid 20s at WOT.

Single Volvo Penta (GM 5.7)