During my first training day on the boat I noticed an issue with the generator. Blue Sky has a fairly capable Cummins/Onan 5kw generator located under the starboard hatch in the cockpit. There is a remote switch located on the wall near the electrical panel that allows the generator to be started and stopped when needed.

The problem was that the generator would not run for more than about 5 seconds. It started easily, and purred nicely…for 5 seconds. After sounding perfectly normal for 5 seconds the generator would shut itself down. Weird.

On the remote switch is a status light that also serves as an error indicator. The light flashes out an error code that can be compared to the troubleshooting chart in the manual. Looking at the indicator I counted two flashes. So I dug out the manual and determined that this code represented a rather generic “Low Oil Pressure” condition. A check of the dipstick showed that the oil was within the acceptable range, and I didn’t see any oil leakage, so I hit the start button again. This time she continued to run.

A few weeks later I was taking the boat out and decided to run the generator as a part of normal maintenance. Again the failure after about 5 seconds, followed by the two flashes. This time, however, no matter how many times I tried. it would not continue to run longer than 5 seconds. I didn’t have time to investigate further, but it went on my to-do list.

I was in the middle of a work project and felt like I needed someone to take a look. So I arranged to have a local company come take a look. I received an email saying that there was extensive work that needed to be done and that the generator would need to be removed from the boat to complete the repairs. So I decided that I needed to investigate the problem more deeply by myself before committing to what sounded like a significantly costly repair.

With multimeter in hand I headed for the marina. When I reached the boat I became somewhat skeptical that they had even looked at the generator. I proceeded to disassemble the generator enclosure to access the innards of the little diesel. What I was looking for was the oil pressure sender. This is a small canister that is mounted to the engine block that senses the oil pressure and sends it to the electronic controller as a resistance.

In the old days an oil pressure sender would have been wired directly to an oil pressure gauge. It would be up to the operator to watch the gauge for unusually low or high oil pressure, and manually shut down the engine if necessary. Modern engines have electronics that monitor these situations and take preventative action to save the engine from damage. My theory was that the electronic monitor was receiving bad information and shutting down the engine as a protective measure. I decided to check this theory by bypassing the sender.

I disconnected the sender from the wire that provides the impedance to the controller and I measured the resistance with my multimeter. It should have been at least 100 ohms but it was showing something completely out of whack. So I figured this must be the problem. To test the theory I tried to start the generator with the sender disconnected, and it behaved exactly as before…shutting off after 5 seconds. Then I shorted the wire directly to the engine block and started it up. In this configuration it continued to run nicely.

So I removed the sender from the engine and immediately saw that it was significantly rusted. So I was pretty confident that this was the problem, but I couldn’t be sure without replacing it. Unfortunately I couldn’t find one locally so I had to order one online and wait until the following week to do the repair. I reinstalled the old sender in the mean time just to keep the salt air from getting at the engine.

I ended up ordering two of these senders. One of them had the exact item number listed in the parts manual, and the other was a generic replacement part that probably would work on a lot of engines. The generic one was about half the cost, but I wanted to know what the difference was. The main difference I noticed was the cheaper one was stamped metal with a thin layer of anti-corrosive coating. This is the same material that the old one was made. The official one  appeared to be made of stainless steel. I began to think that maybe this had happened before, and the only replacement available was the generic type instead of the “marine grade” version.

Back at the boat I installed the new sender in about five minutes and was relieved to be rewarded with a generator that once again started and ran without trouble.

By the way, I noticed some other corrosion inside of the generator enclosure, and I am sure it could stand to be cleaned and serviced at some point. The oil pressure sender was easily accessible from the exposed end of the engine. Pulling the generator for this task would have been completely unnecessary. Although the part was a bit pricey at 50 bucks, I was able to solve the problem. I can’t imagine how much I would have spent if they had removed the generator. Lesson learned. From now on I will always attempt to solve the problem myself.