ONAN 20 kw Over rev shutdown

[doc g]

If you watch the Hertz meter and it changes the rpm has changed . It could sound as if it’s revving if it’s not getting enough water too . Also the low oil pressure, over heat, exhaust temp shutdown will take one of the breakers and over rev will take out the other ....Pat

[bigbill]

does it have a mechanical fuel lift pomp? i had an older onan 15 kw that the fuel pump leaked fuel into the crankcase and made it over rev because the oil was full of fuel

[Passages]

Good info guys. I agree, try the simple stuff first.

I noticed the RACOR sight bowl seemed dark so I went and replaced the element. Plan to replace the impeller today. It's only 1 and half year old with 150 hours, seems to spit out a good amount of water, but hey, lets give that a try as well.

I was going thru the PO's spare parts box an saw a fuel filter marked 20kw. It's not a RACOR so it must be a secondary. A little aluminium retangular boxy thing. I didn't even know it had a secondary fuel filter. Hmmm.....

Can fuel starvation cause an engine to race?

[doc g]

rectangle box thingy is secondary fuel filter and fuel starvation will cause the engine to bog down and lose rpm not over rev. If you look at the service/operators manual it will tell what faults cause what breakers to open........Pat

[Passages]

Replaced secondary. Now I can't get fuel to prime. Said heck with that and began to replace impeller. Now the new impeller is in the pump but the pump is not marked input/output and of course I did not make a note of proper orientation while pulling it out.

So, is there an easy way to tell which raw water pump port is input? Right now I have it input rw, short span with the bronze compression piece, then ouput. My gut tells me it should be the other way but I'm not sure.

I needed to keep repeating "Boating is FUN"

[Passages]

Looks likes I had the pump right to begin with.

Sometimes, when you're sweaty, greasy and frustrated, you just need to take a step back, pour yourself a cold one and do something else for a while, lest you over think things and screw it up even more.

[doc g]

on mine the upper hose connection is in and the lower is out to the heat exchanger. It really does not matter which way you put the impeller in anyway .....Pat

[Passages]

Had the PO over to the boat yesterday. Told him about my over rev, shut down issue. He immediately knew the problem and the solution.

The primary RACOR is shared by 2 generators. If the inactive generator is not valved off, the other genny will, after time, begin to suck air, over rev and auto shut down.
Said it happened to him several times before he figured it out.

Lesson: Always try to stay on good terms with the PO.

[Pascal]

Not sure how air being sucked in could cause an over rev... I also fail to see how air could get sucked in from the other gen fuel return, injectors, injector pump secondary and the lift pump. I guess I ve seen weirdest glitches but it seem a bit far fetched

[doc g]

that means you are sharing a fuel source for both generators, not a good idea IMO, if you have a fuel issue with one you have it on both.If you had a air leak in the return line of the non operating generator I suppose it could suck air into the operating one. Also the return line usually dumps into the top of the tank if the level in the tank is low enough yeah you can suck air . I would assume Viking did not set it up that way. Are you finding air in the system and having to reprime the gen before it will restart?? Again , fuel starvation can't cause over rev ....Pat