Onan Generator

[capttonyf]

We have an Onan 8.0KW with approx. 4500 hrs. Before I call someone to look at it I thought I'd ask to see if anyone has any insight to what my problem might be.

Gen starts and runs fine with NO Issues at all until just recently. Still starts and runs great but occasionally after it's been running for a while, could be an hour or could be 4 hours it will start surging, you'll hear the engine rpm jump up and down, more so than it should when something heavy like an A/C unit would kick on so I don't feel it's a load issue.

I changed the fuel filters and ran it at the dock for like two hours and it was fine and figured that maybe it was the fuel that was the issue, and thought I solved it. But the the last time we were out, maybe about 4 hours into the trip it started surging agian, then shut down. I checked all the fluids, made sure it was pumping water and restarted, and it ran fine for the rest of the day. Then another day while running the systems At the dock it was fine again for an hour or so then it started surging and shut down. Checked it and again it was fine.

Like I said, anyone else ever had this happen?

Thanks

Tony

 

[GJH]

Have you looked at the ampere meter while it is doing this? I had an issue once when one of the AC control boxes randomly would start sending on/off signals to the AC pump, with the AC "off". Caused something like what you described, but nothing close to shut down.

 

[captddis]

I would look at the electric fuel pump. There is a filter inside the pump. If the pump is original, I would replace it.

 

[capttonyf]

I would look at the electric fuel pump. There is a filter inside the pump. If the pump is original, I would replace it.

Thanks I'll check it. I'm assuming it's like a screen type filter if it's inside the pump? Not sure if pumps original or not, it's never been changed since we've owned the boat.

Tony

 

[dottieshusband]

Had the same symptoms on my 20kw mdl4. Got good advice (from Captdis) that pointed to an air leak in the fuel system. In my case, the lift/transfer pump had a small leak that allowed some air in. The pump case cover had 6 screws, some of which had vibrated loose. There is a rebuild kit for the manual pump on the mdl4. I bought one for 160 bucks last week.

 

[Plan B2]

Where did you find the rebuild kit?

 

[dottieshusband]

Ebay

http://www.ebay.com/itm/200891310681

 

[GJH]

I don't dispute the fuel system suggestions, but still, the first step is to check the actual load reading while the problem is taking place.

 

[Plan B2]

thanks for the link

 

[capttonyf]

I don't dispute the fuel system suggestions, but still, the first step is to check the actual load reading while the problem is taking place.

I will do both. Obviously starting with the easiest thing first. "Looking at the Meter"

Thanks again

Tony

 

[fissioneng]

How much surging? A few amps or 10 amps?

I have an 8 kw MDKD that will surge slightly (a couple of amps) when a resistive load is on by itself, usually the water heater. It stops when the AC or other motor turns on.

As far as shutdowns, I chased intermittent shutdowns for a whole summer. It turned out to be a bad fuel pump. Quick, easy, cheap replacement ($100 Facet at Pep Boys).

 

[capttonyf]

How much surging? A few amps or 10 amps?

I have an 8 kw MDKD that will surge slightly (a couple of amps) when a resistive load is on by itself, usually the water heater. It stops when the AC or other motor turns on.

As far as shutdowns, I chased intermittent shutdowns for a whole summer. It turned out to be a bad fuel pump. Quick, easy, cheap replacement ($100 Facet at Pep Boys).

It surges the engine RPM a good bit, more than if just some additionl ac power was needed. That's why I initially thought it was a fuel/air issue. That's why the first thing I did was change the filters hoping that would resolve it, and I thought it did, but unfortunately it didn't. I didn't have time to check much more before heading out of town so I had the guy that takes care of it for us checking somethings and now I'll have him check the things everyone has mentioned. If that doesn't work then I guess I'll be calling the mechanic.

Tony

 

[GJH]

Ebay

http://www.ebay.com/itm/200891310681

Great find, I guess that guy saw the void in the market. Those things were like the Holy Grail around here for a long while. I never needed one, nor had issues getting other parts for my MDL4, but plenty of members here did, often ending up rigging an electric pump instead. If we still had the boat I would buy one of those as a spare.

Not sure if that is the same pump the OP has though, as Dave mentioned an electric pump.

 

[bobk]

Do you have a vacuum gauge with tell tale needle on the Racor? You may have a transient plug of crud getting into the fuel pickup.
Bobk

 

[dottieshusband]

Tony, mine would run normally for a good while then would hunt with the rpm's going up and down about 400 rpms. I thought it was going to die also, but then it would smooth out and run normally until it would do it again. Fixing the air leak at the transfer pump took care of it.

 

[capttonyf]

Tony, mine would run normally for a good while then would hunt with the rpm's going up and down about 400 rpms. I thought it was going to die also, but then it would smooth out and run normally until it would do it again. Fixing the air leak at the transfer pump took care of it.

This seems to be exactly what it's doing, or was doing. Since I've started this thread it's manage to somehow fix itself, go figure. It's been logged now running for a total of 13 hours, 8 hours at once, then 2 hours and then 3 hours. It appears to have fixed itself since I've changed the filters and looked everything over etc. I'm still concerned it will fail again the moment I NEED it to work while on a trip. I'd like to fix it for real but I can't fix what's not broke. Doesn't that seem to be the trend of a boat sometimes, works perfect at the dock but the minute your out and about something fails. I'm still thinking about having a professional look at it but I'm still not sure. I going to have my friend that takes care of the boat for us, take it out and use it this weekend and see what happens, then make a decision after that. For everyone that replied, thanks for the help and ideas, I really appriciate it.

Thanks Again

Tony

 

[polarizer]

what year unit is it, and does it have one of those electric mechanical shut down solenoids? If so, you may want to observe what that is doing during the surge.

 

[capttonyf]

what year unit is it, and does it have one of those electric mechanical shut down solenoids? If so, you may want to observe what that is doing during the surge.

I believe it's original, so a 1990. It does and I will watch the electric shut down selenoid.

Tony

 

[REBrueckner]

Bill Allen and I experienced something similar aboard his 43 Hatt with a 7.5KW ONAN while underway from NJ to Fla. It would run for different periods of time, maybe 15 minutes to an hour or so, then shut down.....I spent several hours bypassing every safety device I could find thinking something was malfunctiong.

Eventually Bill got a long shot piece of advice from an Onan repair guy: Check the fuse holder in the shutdown circuit. Sometimes the spring holding the fuse fatigues from heat and opens the circuit....Silly right, what are the chances....

So Bill stretched the srping by hand, put it back in place....VOLIA we relaxed with drinks. Of course we had been doing that anyway, but now it was fun!!

 

[capttonyf]

Bill Allen and I experienced something similar aboard his 43 Hatt with a 7.5KW ONAN while underway from NJ to Fla. It would run for different periods of time, maybe 15 minutes to an hour or so, then shut down.....I spent several hours bypassing every safety device I could find thinking something was malfunctiong.

Eventually Bill got a long shot piece of advice from an Onan repair guy: Check the fuse holder in the shutdown circuit. Sometimes the spring holding the fuse fatigues from heat and opens the circuit....Silly right, what are the chances....

So Bill stretched the srping by hand, put it back in place....VOLIA we relaxed with drinks. Of course we had been doing that anyway, but now it was fun!!

Funny you mention this about the fuse because one of the last times the fuse popped "Before this surging shutting down problem". The safety shut down fuse popped and gen wouldn't run, would start for a second and shut down but the fuse didn't look like it had popped, it looked like it was pushed into the click position just like it should be. So I called my mechanic and said try to see if fuse popped but is stuck in place so I grabbed a pair of needle nose pliars, realized it was loose and pulled it out until it click/grabbed and then pushed it back in. Like magic if fired up and stayed running perfectly for a few months until this surging started. So I bet your right and it may have something to do with that wore out spring and it may be that button is fluttering, causing it to surge. One more thing to check. Thanks for all the insight everyone

Tony