Generator starts then cuts off

[bill209]

1998 Onan 5kw generator

The generator will cut off soon after starting (‘soon’ will be described shortly)
However, if I push the bypass/glow plug button before it shuts down completely the motor keeps running and will run it as long as I keep the button pushed.

it is my understanding that this switch bypasses several engine checks, such as oil pressure, so that the engine can start. I have very rudimentary knowledge of engines and am unsure how best to troubleshoot this issue.

One possible clue: the first time I start the engine it runs for a full minute before shutting down. Any subsequent starts the engine shut down within a few seconds. If I wait 15 minutes or so before trying to restart the engine it will run the full minute again.

Any thoughts on how to proceed?
Thank you!

[note: I am attempting to get the boat home, which is about a two week journey. I contacted two local boat service shops and they both refused to take a look at the generator; one because they were too busy marinizing boats, which is understandable, the other because the mechanic said he didn’t want to work on the generator because it was too old. An attitude I’m glad my doctor does not hold. ]

 

[lwarden]

You might want to take a look at the wiring, specifically the wires to the temperature and oil pressure senders. It could be one of those is malfunctioning or the wires/connections leading to them has increased resistance due to a bad connection.

It might help us to help you if you post the maker and model of the generator.

 

[tiltrider1]

Sounds like either the over temp sensor or the oil pressure sensor has failed. Both should be fairly easy to acquire and replace.

 

[High Wire]

Wow. 1998 is not old! You are correct that the preheat switch will bypass the trips when held but it also turns on the glow plugs which is not good for them long term.
I’m going to assume you don’t have a schematic nor DVM. Keep trying to find a generator mechanic to come out. This is not hard to diagnose for someone with some electrical skill.

 

[Comodave]

Can you bypass eash sensor one ar a time to determine which one is causing the saule.

 

[ofer]

Onan MDKAL with Kubota Engine trouble shooting

I have a couple of issues not sure they are related. able to start the generator after a few tries. seems to run ok although lots of black smoke and what looks like diesel residue coming out of the exhaust. gen will run for about 5 minutes and then will trip the check engine breaker. if i...

www.trawlerforum.com

lots of info on my issue above. did everything and couldn't figure it out. generator removed from the boat and a new one is not going in.

 

[NWboater2]

I had a similar problem on an NL673, twice. First time I replaced the control panel cuz my model had a known problem breaker. That worked for a while but then it happened again. S3 replaced the water temperature switch. It runs like a top now. In hindsight that may have been the problem the whole time. Good luck!

 

[long-cours.62]

Did you check the sensor for raw water ?
I had this problem , it was this sensor who don't work.

 

[O C Diver]

1998 Onan 5kw generator

The generator will cut off soon after starting (‘soon’ will be described shortly)
However, if I push the bypass/glow plug button before it shuts down completely the motor keeps running and will run it as long as I keep the button pushed.

it is my understanding that this switch bypasses several engine checks, such as oil pressure, so that the engine can start. I have very rudimentary knowledge of engines and am unsure how best to troubleshoot this issue.

One possible clue: the first time I start the engine it runs for a full minute before shutting down. Any subsequent starts the engine shut down within a few seconds. If I wait 15 minutes or so before trying to restart the engine it will run the full minute again.

Any thoughts on how to proceed?
Thank you!

[note: I am attempting to get the boat home, which is about a two week journey. I contacted two local boat service shops and they both refused to take a look at the generator; one because they were too busy marinizing boats, which is understandable, the other because the mechanic said he didn’t want to work on the generator because it was too old. An attitude I’m glad my doctor does not hold. ]

Most generators with a bypass circuit, don't usually allow 1 minute for bypass. I would say it's more like 15 seconds. So, I would be looking for something that is failing after the bypass circuit times out. Put another way, initially it takes a minute to fail, then after restart, it fails as soon as the bypass circuit drops out.

Is there an exhaust noise change? If the generator is equipped with a raw water flow sensor, and the flow stops, the sound of the generator without water flowing to the exhaust, should be louder.

Have you checked the oil level? Oil drains back into the pan after the engine is stopped. After the engine starts, it might take a minute before the oil pump sucks air and the oil pressure drops below the shutdown level.

Ted

 

[Duvie]

I had a launch with a Westerbeke 20b two. As I recall when the switch was put in preheat, it also powered the fuel pump. After the engine started oil pressure would start the fuel pump. This sounds like the type of circuit you have. They delay is the engine using up any fuel it can before it dies. The oil pressure or other safety may be giving you issues.

 

[Iggy]

Is raw water flowing? Have you checked the impeller?

 

[Cigatoo]

Like Iggy said. The sensor (s) may be doing their job. Ck the basics. Raw water flow, correct amount of engine oil, oil pressure, etc.

 

[Greg QS]

I had a problem like this. It would run for a few days and quit. Would up being a lead to one of the relays in the box on top. It heated up and melted. I replaced the connection and relay and all good last season. Some times it is jut better when things break. Intermittent problems are so hard to find sometimes.

 

[Mac G]

I agree with Iggy.
Check your raw water flow.
Had similar situation last year wherein unit shut itself down quickly after startup because impeller broke.

 

[Greg QS]

I also had water flow issues after purchasing the boat. Genset would run for a day or two and then shutdown . Pulled off the end cap to the heat exchanger, and to my supersize a handful of impeller blades . Good thing I paid a shop to change the impeller. They told me the blades were missing. Apparently they did not go looking for the missing blades. Humm. Not using them again.

 

[jgwinks]

They would have to charge extra for that, likely wouldn't do it unless you asked them to. And often when you find pieces in the system, they're not all from that last impeller. Could be the last two or three as well.

 

[Greg QS]

The point was they did not even recommend it. The new impeller was suppose to fix the shutdown issue. It did not of course. They were also hired for engine impellers and oil changes on 2 genset and engines and fuel filters all. The port engine fuel filters on the engine were all hand tight and the oil filter was loose. They were lucky I found the leaks before I seized and engine.

 

[bill209]

Omg you guys kill me.

I do believe there are two problems as there was a BOGO sale going on when I bought them; I believe the oil pressure switch is bad as the wire terminal seemed loose, and well, the pic of the impeller speaks for itself.

I have parts coming in over the next few days and will hopefully be up and running soon!

I really appreciate the great advice. This is the best I have felt about fixing this problem in several weeks. Thank you!

 

[Greg QS]

Go looking for the missing piece. It is most likely in the heat exchanger.

 

[OldDan1943]

There are 2 sensors, oil a water temp. Carry spares. Impeller, carry 2 spares. The glass fuse, 2 spares. Put them in a box, label the box and remember where you put box.