Mercruiser 502's Water Pump by-pass
 

Is it possible to remove the water pumps without damaging the engines and relying on the sea pumps (impellors) only for water cooling? What is the estimated HP gain. I was told one could use a water pump by-pass kit and remove the water pump and gain ~ 30 hp. Please advise.

my engine guy said don't do it. can cause steam pocket's or hot spot's. my uncle is a prety top engineer and he say's the same. not worth it unless running blower's maybe.

Yes it is possible. You should not have a problem with steam pockets, as long as the water constantly moves. The biggest problem I have seen is water pressure. If you run a thermostat ( which you should), the by passes are not usually big enough to divert enough water. The water pressure builds because of this. You have to move the water at all times. It is constantly coming in and needs somewhere to go. The stock setup has (2) 1" hoses that bypass water to the exhaust when the thermostat is closed. The typical aftermarket crossover and thermostat housing only have (1) 1/2" bypass hose, and it does not divert enough water to stop high water pressures. I have tried drilling holes in the thermostat to relieve pressure. To get the pressure down enough, I had to drill so many holes that the engine would not build temperature. All Merc engines are built to run with about 180* temp. It is not that bad on the carb motors, but efi engines get stuck in cold start mode and run rich, sooting up the transom. However, you can gain almost 20 hp by ditching the circulation pump. Hope this helps, Eddie.

Is it worth all the trouble and money to set it up for possibly 1mph? I wouldn't do it, IMO.

IMO, not worth the trouble or expense for the gain.

So if you wait until your engine(s) are at running temp (thermostats open) to rev them up then there would not be a risk of creating hot spots due to high water pressure (the thermostat would dump to the exhaust system)?

I wouldn't do it, your stock sea pump will not really produce enough flow. I was told you would need to upgrade your sea pump to a two stage pump ($$$$) if you are going to put a crossover in.

Not true .....If the sea Pump moves enough water with the circ pump it will pump enough water without the circ pump ......the stock circ pump can move a TON of water ...Haveing said that .... unless you want to invest in the time and money to "fine tune" your thermostat and also install the capablility to monitor water pressure dont do it ...m

I just have to ask; is it really possible that the engine driven water pump uses 20 HP? I really find this impossible to believe. I have 3" gasoline powered pumps that we use to pump out foundations and manholes. They move infinitely more water (319 Gallons per minute) than a little belt driven water pump. And the Honda engines on these pumps are only 7HP.

Can somebody answer my question above? TIA