Circulating Water Pump?

[OkieDave]

Why do we need the circulating water pump on a mercruiser motor? my 502 EFI MPI in my 26' Firehawk Cat has a water pump bolted to the front of the motor that is fed in a roundabout way from the sea-water pump. why can't I just get rid of the circulating pump and let the sea-water pump put the water thru the motor?

[737jetmech]

The circulation pump on the Mercruiser engines keeps the water pressure in check as well as running temps.
I've tried cross-overs in place of my circulation pumps .
Pros. They look nice , may be a couple HP ???
Cons. High water pressure with Mercury 28 psi pop-off valves installed they were opened all the time at cruise speed and higher.Low running temps 100 -125 even with 142 drilled (for bypass)T-stats installed.Milk shaked the oil in both engines.
I messed with the set up for a couple seasons and finally reinstalled the original circulation pumps.
Bob

[Paul128a]

I have always ran a crossover kit on my small block mercruiser (chevy). My first belt driven Saltwater pump was the one from my heat exchanged 255 TRS, without the heatexchanger, sucking salt water direct, and gave me 70C (158 F) running temperature, using a Volvo 280 drive.
I live in the tropics and salt water temp is around 78F all year round.
I recently changed to an Alpha drive, which has the salt water pump built in the drive, and I now run 80C (176F) running temperature. All of this using a crossover and NO thermostat.
I have run this set-up since last year and never ever have I milkshaked oil. Milkshaked oil I think is a tell-tale sign of water going in the oil and mixing with it, unless the low oil temperatures cause a lot of moisture to form inside the engine and mix with the oil.
I also actually made the crossover myself, using an old chevy water pump, removing all the insides and covering the impeller shaft hole.

[cfm]

The circulation pump on the Mercruiser engines keeps the water pressure in check as well as running temps.
I've tried cross-overs in place of my circulation pumps .
Pros. They look nice , may be a couple HP ???
Cons. High water pressure with Mercury 28 psi pop-off valves installed they were opened all the time at cruise speed and higher.Low running temps 100 -125 even with 142 drilled (for bypass)T-stats installed.Milk shaked the oil in both engines.
I messed with the set up for a couple seasons and finally reinstalled the original circulation pumps.
Bob
100% correct.
Add to this with MPI, you need proper water temp for the computer settings. Run it too cold and the computer will be in " warm up/fuel enrichment" mode and you'll burn too much gas, get black transom, and dilute oil with fuel.
I've tested the recirculation pump vs crossover on a 502 on the dyno with wet exhaust, dry exhaust, with and without other accessories, etc, etc for hp and for water psi + flow. This testing was followed up on the water too.
After a ton of testing - my answer for your application is to keep the recirculation pump !!!!!!