Boat Generator

Generator dies after running for 20 minutes.

What the heck is wrong with it?

The symptom: It dies after about 20 minutes and usually wont restart. So here's a basic test list anyone can do with the right tools.

Tools needed: A good 12vdc Test light, a digital volt ohm meter and an Infrared Thermometer. ( ever been to one of my seminars? LOL)

Theory of how it works.

Most GAS genny's work on this principle. There are 3 "shutdown" safeties. 1) Low Oil 2) Overheat and 3) Low oil pressure. Add number 4 as a bonus.... Ran out of fuel. The pickup is shorter than the engine pickup and the genny will run out at 1/4 tank of fuel.

Testing flow chart. ( make one)

For this job here's how I did it.

1) Ran the genny and used my Infrared, to determine engine temp. Checked Heat exchanger, Exhaust water, and Engine block where the safety switch is located. ( Looks like a Clothes dryer safety) I got 115-126 at all points which is perfectly fine. The overheat safety generally the overheat safety will shut the engine down at 200.

2) When the engine died, I put an ohm meter across the overheat safety to make sure it wasn't weak. The circuit was completed so it wasn't that. If the Ohm meter showed an open circuit, we would have our smoking gun.

3) I put my test light on the single wire to the electric fuel pump and spun the engine. I had power.

4) So when I finally got it restarted, I had left the test light in place to test the fuel pump relay to see if it was intermittantly sticking. ( See video attached) No problem there, but when the engine started dying, the test light was strong..... and so was the exhaust... BLACK SOOT!!!! Ok now we have our diagnosis. Either trash in the fuel or a sticking needle and seat overfilling the carb. A removing of the flame arrestor ( Not reccomended for DIY) confirned, a ton of wet fuel floating out of the carb. So a simple rebuild, with a good filter system will fix this and have her purring. By the way. Most people don't know this but there is a fuel filter inside of the electric pump. If you have the cylindrical vertically mounted pump the bottom cap will twist off slightly allowing replacement of the filter.

Video of troubleshooting a generator: https://youtu.be/WlTTAGW1n3E

How-To: Tips & Tricks For Generator Troubleshooting Submitted By My Friend: Lee Dahlen

Lee is one of the top boat technicians in the country and he has never failed on a fix.

This has to be one of the most irritating symp- toms in the Commander Club these days. You have the standard Onan MCCK 6.5 Gas Gen- set, and it runs great! Then shuts down... In my line of work, I deal with them A LOT!! Most of the time, any other service company will look at it and if it spits out water, they tell you “It’s just old, and either “We won’t work on it” or “It’s time for a new one”. I actually had a surveyor, on a 42 tell me in the survey put down “at the end of it’s service life and needs to be re- placed”. After I gave it some “love”, that genset ran for many years aboard Rob and Jamie’s then “Command Performance” and is probably still running today. I also had another in Texas that went through 3 different techs and literally thousands of dollars, before I got my hands on it. It is also still humming along with a very hap- py client. Let me start by saying, if it runs but doesn’t produce power? Then it IS probably time to replace. The powerplant itself is very complex and parts are hard to find and price prohibitive. We will deal with the engine portion itself.

What’s the love? It starts with an understand- ing of how these old girls work. First, they are a simple 2 cylinder, gas-powered, carbureted en- gine. Think of it this way and the diagnosis and repairs become fairly straightforward. So back to the subject. You have one that runs, then shuts down.

You need the following tools:

 Screw driver ( I like a 6-1 since it gives me 4 bits a 2 nut drivers all in one)

 Adjustable wrench

 1’ of 14 gauge wire with two alligator clips.

 An infrared temp gun. THIS IS A MUST!

Don’t even go forward until you have one. The MCCK has 2 systems that shut down the engine for protection. One is an oil pressure lockout and the other is an overheat. The over- heat is generally the cause of a shutdown. It is a temperature sensor that bolts directly on the right side cylinder head (Looking from the front) It looks exactly like a dryer temp switch if you’ve ever worked on an older clothes dryer. It’s round, the size of a quarter or larger, and has two wires, one on each side. This sensor uses a temperature sensing metal that when reaches a specific temp will open the circuit and shut the unit down. The oil pressure cutoff is a standard oil pressure sender (for a light) screwed into the front area and also has 2 wires on it.

Testing and diagnosis:

Assuming you have checked fluid levels and water output while running:

Overheat: Run the unit until it shuts down. When it does, aim your temp gun at the over- heat sensor where it meets the head. (Metal to metal) Take a reading. The switch shuts off the unit at about 215 degrees. Also you can tempo- rarily, take a jumper wire with two alligator clips and bridge jump the wires and see if it starts. I’ll say strongly, this is temporary to verify. Do NOT leave this circuit jumped and run the set. It will destroy it.

You have to run both tests. Why? I have found sensors that shut down at 160-185 area in which case you have to replace the switch. Your set (Closed Cooled) will run 170 area nor- mally. Also the jumper confirms the switch shut it down.

On the oil pressure: Use the jumper and see if it starts. If it does, remove the oil pressure switch and install a manual gauge. Jump the wires and start the unit. Anything below about 12psi will destroy the engine and it’s time to re- build. Oil pressure has nothing to do with oil level, unless it’s reading 0.

One final tip. On the genset in Texas: This was an interesting situation. After replacing a bad temperture sensor, I found the coolant to be really thick. After talking to the client, it was pure antifreeze. Once we removed half, and added half water, it ran fine. The coolant was so thick that the heat exchanger could not dissi- pate the heat and keep up. Remember, full strength coolant, will freeze, but will also over- heat! Hopefully these tips will help you bring the old girl back to life. They are really hard to kill. And I’m always available if you need help! Cheers!

The last ditch effort on checking everything that can go wrong with a generator