Onan 8K Gen losing coolant

[HandsOnTech]

I am cruising (i.e. fixing the boat in exotic locations). Today’s most pressing issue is the generator. It has been getting much less use since installing the solar panels, but has always run reliably. Yesterday it ran for about five minutes and stopped. I could crank it, but the fuel shut-off solenoid would drop out as soon as I released the Start switch. I finally noticed the Fault breaker button on the control panel. I pushed it back in and the generator started just fine. Until three minutes later when the Fault button popped out and it stopped.

The tray under the engine portion of the generator contained a few ounces of coolant. I don’t remember the last time I looked that closely, so I don’t know how long it was there. I topped up the reservoir with 16 ounces of water, cleaned up the spill, and lined the tray with paper towels to narrow down the location of the leak.

1. Started the generator. It ran normally for three minutes when the Fault button popped and it stopped. The towels were dry.
2. Started again. Ran for three minutes, button popped. Towels were drenched with several ounces of coolant. Replaced with dry towels.
3. Started again. Ran normally for 30 minutes until I turned it off. Towels were dry.

I hate a problem that fixes itself. I have learned nothing and have no idea where to start when it happens again. I tried wiping everywhere I could reach with a paper towel hoping to find a wet spot, but no luck.

Any suggestions for where to look would be appreciated.

I have included photos of a rusted area of concern, but that would appear to have more to do with salt water than coolant. Again, any suggestions.
Thanks

 

[Terry Cox]

Welcome. We too, have the Onan 8KW Genset. Marvelous little machine that has been a gem over the cruising years. That is until she refuses to run. She is equipped with three sensors that were designed for unattended/remote operation; high exhaust temp, low oil pressure, high engine temp. When any one or more of these come into play she will shut down.

We've had a few instances where our machine refuses to operate:

1. One time while running in a very dirty harbor she sucked in a bunch of marine debris and plug the sea water strainer, which stopped water flow causing a high exhaust temp alarm. Took awhile to trouble shoot the problem, but after cleaning the sea water strainer, replacing the sea water pump impeller (due) and resetting the sensor breaker she started right up and ran just fine.

2. The original standard engine fuel filter is a cartridge two micron fuel filter. Too fine IMHO, but when it stops full flow, the engine sputters and stops running. Replaced the original two micron with a spin on six micron filter from NAPA. Saved a bunch of money on the NAPA brand and she seems to like it. Six micron gives ample fuel protection.

3. This past summer after starting her, I always check for water flow out the exhaust, but no water, so shut her down. Pulled the impeller and found a missing vane. Ah ha! Had a spare, so replaced and still no water flow. Long story short, the dealer sold me an after market brand that was slightly different than Onan original. Replaced with new and she pumped water just fine, but...

4. In the process of replacing these impellers I must have damaged the plastic am phenol connector that supplies power to the lift pump, because she would not run for more than a few minutes. She would start and run just fine, then slowly start to run out of fuel and sputter to a stop. That single wire is right next to the sea water pump and the pump cover is a bear to remove and install. It cost me more than a half of a boat buck to find and replace that broken connector that cost under two dollars.

So, time to isolate the problem. No idea how long it has been or how many hours on the engine, but I doubt it is low oil pressure. If it is a hard shut down as opposed to a sputtering shut down, likely something to do with temperature. The first its to make sure your sea water strainer is clear, the sea water strainer cover is on tight and that your impeller has all its vanes. If so, when it does start does it discharged water out the exhaust. If not you may need to prime it. We can discuss that later; a simple and easy process.

Usually it takes a few minutes of running before it gets hot enough to set off the high exhaust temp alarm. Unlikely, but it could be a clogged mixing elbow, depending upon how many hours on the engine. Several years ago we had a small amount of coolant that collected beneath the engine for some unknown reason, then it stopped and has never recurred.

Check the various items that I listed above and please let me know what you find. Yours, like ours, is run by a three cylinder Kubota diesel tractor engine. Very reliable beast when she has what she needs to run. We have almost 500 hours on our 1991 engine; hardly broken in.

The thread that I started awhile ago where we had a similar problem is here: Onan Cummins 8KW Genset Issue

 

[jibes138]

Your coolant leak problem sounds like you are overfilling your coolant tank. Coolant expands when it gets hot which is why they make overflow bottles. The cap is made to release coolant into the tank as it expands and then suck it back in as it cools. If you don't have a "coolant recovery tank" then you can add one pretty easily if you have room to mount it. If you top off the coolant without this tank the coolant expands the cap releases it and it gets all over. Next time the remaining coolant in the tank is less it expands and doesn;t overflow since there is room for expansion and voila no leak. I can't speak to your engine shut down problem and breaker tripping. Sounds like Terry covered it.

 

[Terry Cox]

Hi Dave, our setup has an expansion tank for the Genset and likely his does, too. Good point.

 

[jibes138]

Hey Terry, OK. So given the three minutes dry, three minutes wet, 30 minutes dry scenario I'd still focus on expansion of the coolant as the leak source. In three minutes it is not very hot, next three minutes more so, final thirty minutes coolant already overflowed and now room for expansion. So if the cap isn't an issue where else in the system can it only leak if the coolant expands? Maybe place those towels in assorted places to pinpoint the leak point. Many possibilities exist for leaks, head gasket, manifold gasket, exhaust gasket, heat exchanger, hot water tank connections, thermostat housing gasket, coolant pump gasket, any hose or hose connection.

 

[Terry Cox]

Little comment from the OP. Perhaps he is busy tracking down the fault. Hopefully, we will soon receive an update.

 

[HandsOnTech]

I am back. We just spent three days on the Bahama bank with no land in sight to any horizon and therefore no cell tower.
And anchored in 12 feet of water. One afternoon the wind dropped to zero, creating the ultimate infinity pool.

Thank you for your thought out responses.

I have tried starting the generator several times, but since that 30 minute run I have not been able to get it to run more than five minutes when the fault button pops and the fuel cut-off solenoid drops out. When I pushed the Fault button back in and immediately restarted, it only ran for ten seconds. This makes me think the Fault is caused by high temperature.

The sea strainer is clean, a normal water flow appears to be spitting out of the exhaust, the fuel tank is full. There is no sputter of any kind. The solenoid simply shuts it down.

How is the coolant pumped? There is a cover on the engine at the end opposite the electrical generator. Is a fan belt involved?

What mystifies me is the fact that despite this almost consistent string of faults, it managed to run perfectly one time.

 

[Terry Cox]

How is the coolant pumped? There is a cover on the engine at the end opposite the electrical generator. Is a fan belt involved?

Yes, the belt drives the alternator and engine coolant circulation pump. Worth a check. Thank you for the update.

 

[twalker H260]

I think you may be chasing two unrelated issues. I don’t know exactly which model generator you have but I did come across this manual that has a schematic that looks like it may be close to yours.

https://onan.xmsi.net/981-0600%20Onan%20MDKC%20MDKD%20series%20Marine%20Diesel%20Genset%20Installation%20manual%20(05-1990).pdf

Schematic for engine control is on page 8-7. You mentioned early on that the fuel solinoid is/was dropping out when releasing the start/stop switch until you reset the fault circuit breaker? It appears that circuit breaker is to control the fuel solenoid, fuel solenoid relay, fuel pump and a few other “electrical” related items. Doing a bit of an Internet search seems to indicate that wiring issues in these components can cause the fault breaker to trip.

i would look at the electrical connections - particularly those that are in the areas you Indicate are rusted, for loose or corroded connections.

If you have the model number available it may be possible to find its service manual with the schematic for your system.

Most over temp switches I am familiar with are auto resetting bi-metallic switches that would not cause a breaker to trip. A loose or corroded connection however can cause randomly timed events based on how things are leaning, shaking, rattling, rolling, getting bumped, humidity and ambient air temps - among other influencing factors!

 

[Terry Cox]

The model number of our 1991 Genset is 8MDKDR31457C, which is likely the same/similar as the poster's. The three sensors on our engine will trip the breaker when specified conditions are met; high exhaust temp, low oil pressure, high coolant temp. I have never had them self reset. Once any one or more of these sensors trip the breaker, the engine fuel supply shuts off. Best to trouble shoot why. Your suggestions do help in looking for other causes such as corrosion, loose connections, etc.

We have had a few instances where our engine stopped running, which I listed in my reply above. Unlikely it is low oil pressure. It appears to be high temp related. Each system needs to be checked to rule out the cause. The poster said he observed sea water discharging from the exhaust port, so unlikely the sea water coolant system. The other possibility is the captive coolant pump; is it circulating coolant through the engine; perhaps a clogged heat exchanger.

 

[HandsOnTech]

I think you may be chasing two unrelated issues. I don’t know exactly which model generator you have but I did come across this manual that has a schematic that looks like it may be close to yours.

https://onan.xmsi.net/981-0600%20Onan%20MDKC%20MDKD%20series%20Marine%20Diesel%20Genset%20Installation%20manual%20(05-1990).pdf

Schematic for engine control is on page 8-7. You mentioned early on that the fuel solinoid is/was dropping out when releasing the start/stop switch until you reset the fault circuit breaker? It appears that circuit breaker is to control the fuel solenoid, fuel solenoid relay, fuel pump and a few other “electrical” related items. Doing a bit of an Internet search seems to indicate that wiring issues in these components can cause the fault breaker to trip.

i would look at the electrical connections - particularly those that are in the areas you Indicate are rusted, for loose or corroded connections.

If you have the model number available it may be possible to find its service manual with the schematic for your system.

Most over temp switches I am familiar with are auto resetting bi-metallic switches that would not cause a breaker to trip. A loose or corroded connection however can cause randomly timed events based on how things are leaning, shaking, rattling, rolling, getting bumped, humidity and ambient air temps - among other influencing factors!

Thank you for the installation manual. Here is a service manual I found.

https://onan.xmsi.net/981-0502%20Onan%20DKC%20DKD%20MDKC%20MDKD%20Genset%20Engine%20Service%20manual%20(03-1994).pdf

I will read the manuals in detail shortly. Today’s top priority is replacing the Yanmar impeller, as the engine sounded the Over Temp alarm yesterday and I had to sail into this tiny harbor. Fortunately, it was early and I was the first one here.

 

[HandsOnTech]

I feel foolish for having to ask, but how do you remove the cover from the end of the engine? It is firmly attached and so snugly tucked away in there that I cannot see or feel any fasteners.

 

[HandsOnTech]

Ok, after several iterations of video recording with my cell phone I have determined that there are three attach points for the cover. I have used a 10mm socket and the Braille method to remove the nut high on the port (solenoid & control) side and the bolt on the bottom that only needs to be loosened, not removed.

The third attach point appears to be on the top to starboard near the belt tensioning bolt. Still looking.

 

[Terry Cox]

Ok, after several iterations of video recording with my cell phone I have determined that there are three attach points for the cover. I have used a 10mm socket and the Braille method to remove the nut high on the port (solenoid & control) side and the bolt on the bottom that only needs to be loosened, not removed.

The third attach point appears to be on the top to starboard near the belt tensioning bolt. Still looking.

It has been several years since I've had the cover off, but I think you have it at three. A bit difficult to remove, but doable.

 

[HandsOnTech]

Ok, after several iterations of video recording with my cell phone I have determined that there are three attach points for the cover. I have used a 10mm socket and the Braille method to remove the nut high on the port (solenoid & control) side and the bolt on the bottom that only needs to be loosened, not removed.

The third attach point appears to be on the top to starboard near the belt tensioning bolt. Still looking.

It has been several years since I've had the cover off, but I think you have it at three. A bit difficult to remove, but doable.

Is the third a nut or bolt, or is it a Chinese puzzle move? The plumbing for the manual bilge pump seems to be pressed up against the shield, and I cannot tell if that is the problem with removing it.

 

[Terry Cox]

Sorry, do not recall.

 

[HandsOnTech]

Sorry, do not recall.

When you removed the cover, did you do it in place or did you slide the generator forward?

 

[Terry Cox]

Did it in place, I think. I know I never moved the Genset. The reason I took it off was to inspect the small alternator that seemed to be acting up. But as it turned out there was a ground wire that had become loose. If I remember right it is an AC alternator, not DC, which I found odd at the time.

 

[HandsOnTech]

Problem confirmed, but yet to be solved. The remnant of the fan belt is hanging down below the cover, so that is the cause of the problem.

I have contacted Cummins for help. The first customer support rep I spoke to repeated three times during the conversation that I should bring my RV to their service facility and they would take care of it. Obviously he was reading a script on his screen.

The second attempt got me some PDF manuals, but none show the guard in detail.

I am sure that this is obvious if the unit is sitting on the workbench in a well lit shop. Below is a photo I found on the internet. The cover I am trying to remove is on the left. I have removed the nut on the left side and the bolt on the bottom, but something is still holding it.

 

[Terry Cox]

Glad you found the culprit; no coolant circulation. I'm wondering here whether the leak source is from a failed or leaking circulation pump bearing. I've had coolant pump bearings freeze up that caused the belt to either burn up, break or spin off. How many hours do you have on the engine?

I wished I could be of more help on what is holding the cover on. I do remember that it was a difficult task due to the limited space. While you're in there I would replace the pencil zinc in the heat exchanger.