I was having an engine overheating problem and I called Brian Smith from American Diesel. After explaining my problem, he immediately said something like, “Sounds like you broke a fin off your impeller that moved to your oil heat exchanger restricting the water.”
When I examined the oil heat exchanger, there it was, part of a fin from the impeller, blocking about a third of the water flow. I was blown away that this little piece of rubber could cause an overheating problem. My immediate thought was, “This is a really poor design. There has to be a way to prevent this in the future.”
As I started to review the raw water system, the obvious problem was the water flowed from the impeller to the oil heat exchanger, then to the coolant heat exchanger. So it was designed so the first exchanger in line was the smaller heat exchanger, where a small piece of the impeller can block a significant percentage of the flow, followed by the larger exchanger, where the same piece would have little effect. My first thought was to just re-plumb the system so the coolant exchanger was first, followed by the oil exchanger. I did some temperature monitoring and the temps from one exchanger to the next were within a couple of degrees, so re-plumbing would not have been a problem temperature-wise. But the plumbing was not that simple since the coolant exchanger is not a simple flow-through, but a split system.
My next thought was to put something in the line between the impeller and the oil heat exchanger to “catch” any debris headed for the exchanger. After playing with some designs of my own (none of which worked nor were cost-effective), I came across an inline filter sold by Groco that was made for the job at hand (model WSB 1000-P; best price I found was $45 at Discount Marine). It, along with 2 fittings to adapt the one-inch hose to the filter and a hose to replace for the current copper pipe in the system, snugged right in the area between the impeller and the oil exchanger and left room to access the impeller cover.
In my case, the installation was easy. I removed the old pipe and hoses and turned the fitting on top of the impeller housing 90 degrees so it pointed away from the engine. I used the existing short hose to connect the filter to the exchanger, and added a pre-formed NAPA 7545 hose ($13 on eBay) to connect the impeller housing to the filter. (Note: the filter has a flow direction, so don’t do what I did the first time and install it backwards.)
We likely have all heard stories of impellers coming apart shortly after installation due to a defect or poor storage. For less than $150, I greatly reduced the possibility of a reoccurrence of the same problem, and I can now quickly see if the impeller is coming apart. This gives me one less thing to be concerned about and more peace while cruising. But just for added comfort, I also added temperature sensors with an alarm on both engines to give an early alert of an engine overheat.