How to Install a Raw Water Pump
Without a water pump, an engine will overheat. I ended up replacing my original pumps with a 12 volt inline water pump.
How Much Does a Water Pump Cost?
The original pump for the sea water (called a raw water pump) was driven by a belt coming off the flywheel of the engine. The pump was made by Jabsco, and was proprietary to OMC. That means that when OMC went out of business, the pump went out of existence. When I first purchased the Rock ‘n Row, one of the pumps were seized and needed to be replaced. I was able to find a brand-new pump on eBay for $600. It was the only one I could find despite several days looking on the internet and calling around to different part suppliers.
As painful as it was, I forked over the cash and got the replacement pump. When I went to install the new pump, I noticed that the mount for it on the motor had broken. I jimmied a fix, but the belt was just slightly off center. About two hours into the running of the engine, the pump starting whining terribly and it stopped pumping water. I quickly shut down the engine and brought the boat into the marina on one engine. After removing the pump, I found that the impeller had shredded itself; presumably because the pump had been mounted slightly off-center.
How to Change a Water PumpNever being a very mechanically minded person (I’m an electrical engineer), I decided these belt driven pumps were archaic and too frustrating and expensive to work with. Besides, I had no clue how I was going to go about fixing the mount on the engine. I started doing research and discovered Shurflo 12 volt pumps.
The origonal spec for the Jabsco pump was 900 gallons per hour (GPH) at 4000 RPM. The Shurflo Piranha livewell pump is rated for 1100 GPH, which exceeds those specs. So I knew it *should* work. Everyone I talked to advised me against it however. I couldn’t find anyone who had done an electric retrofit or knew how to install a water pump in this way.
There was one main difference that I discovered the hard way. The Shurflo pumps are designed for high volume, but very low pressure. The first year I ran the engine on the electric pump, it worked great, but the wet exhaust consistently had more steam than the other engine with the belt driven pump. The engine also consistently ran 10 degrees celcius warmer. I figure out later that I didn’t have enough pressure coming from the 12 volt inline water pump. Over the course of that first year, I had to replace the pump twice. I believe this was because I was simply running it too hard. However, at $50 a pop and only 15 minutes to replace in the field, I didn’t mind replacing it. I keep two spare pumps on board at all times now.
On a recent trip to Rosario Resort, I noticed that the Jabsco pump on the other engine was leaking profusely. With a year of successful trials and lessons learned, I decided to go all electric. I also learned my lesson about the pressure and put two 12 volt inline water pumps on each engine.By putting the pump in series, I was able to double the pressure and maintain the same water volume (1100 GPH). At first I tried putting them in parallel, which should have doubled my water flow but kept the pressure the same. That didn’t work very well and I didn’t notice that the engine ran any cooler. I mention it here in case anyone tries it. In-series is definitely the way to go.
At this time, Ken is also experiencing issues with the raw water pump on his boat. Being a mechanically minded person, he is hesitant to go with an electric solution. We looked at the specifications for his raw water pump, which is 900 GPH, so this solution should work just fine. In fact, this type of 12 volt inline water pump should work as a replacement for most boats, including the 454 water pump, a mercruiser sea water pump, and many others.