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Onan shuts down under load without shutdown codes


Mark Pitt
 

On my first sail trip of the season, my Onan MDKAV shuts down under load after 15 to 20 minutes.  No blinking codes.  Does not matter is the load is from the watermaker or AC.  It does not shut down from a charger load, or any load under about 15 amps.  I changed all the fuel filters but that did not help. Plenty of water coming out the exhaust.  Overheating should generate a shutdown code in any case.

Any ideas?


Mark Pitt
Sabbatical III, SM419, Rhode Island, USA


 

Mark,

I know that you probably know this, but "plenty of water coming out the exhaust" is not a measure of sufficient water, or of the colling system. The only measure of the cooling system is the temperature difference between the exhaust elbow and the engine block or oil temperature. The normal operating temperature of the block is around 80C and if the cooling system is working the exhaust elbow should be around 50C. To eliminate the cooling system as a problem, measure these temps. BTW, I cannot count how many times I have been told "plenty of water" when it was not enough water coming out.

Once the above is eliminated and the fuel system is eliminated (is the fuel pump within 8 years of age and the filters new), it is likely a sensor issue. Some model Onans have Normally Open (NO) sensors and some Onans have Normally Closed (NC) sensors. Once you determine (see below) which you have it is simple to bypass one sensor at a time by either disconnection one wire from the sensor for NO sensors, or jumping or connecting the two wires for NC sensors. Don't do this without monitoring the exhaust temperature and ensuring it does not rise above 60C.
image.png

Here is a common sensor issue (if you have the flow sensor installed). This sensor was partially clogged. Sometimes it worked and other times it shutdown the Onan. Also this sensor was found to be oriented where the debris would fall into the sensor. When it was reinstalled, it was oriented correctly (last photo):
image.png

Sensor oriented incorrectly. Sensor pipe should be turned 180 degrees:
image.png


CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
View My Training Calendar


On Wed, Aug 12, 2020 at 8:22 AM Mark Pitt <mark_pitt@...> wrote:

On my first sail trip of the season, my Onan MDKAV shuts down under load after 15 to 20 minutes.  No blinking codes.  Does not matter is the load is from the watermaker or AC.  It does not shut down from a charger load, or any load under about 15 amps.  I changed all the fuel filters but that did not help. Plenty of water coming out the exhaust.  Overheating should generate a shutdown code in any case.

Any ideas?


Mark Pitt
Sabbatical III, SM419, Rhode Island, USA


 

And, I should have said, once you eliminate the cooling system, the fuel system, and each of the sensors, I suggest that it's time to get an Onan tech.

Good luck!

Best,

CW Bill Rouse 
Amel Owners Yacht School
+1 832-380-4970 | brouse@...
720 Winnie, Galveston Island, Texas 77550 
www.AmelOwnersYachtSchool.com 
Yacht School Calendar: www.preparetocastoff.blogspot.com/p/calendar.html


   


On Wed, Aug 12, 2020, 9:28 AM CW Bill Rouse via groups.io <brouse=gmail.com@groups.io> wrote:
Mark,

I know that you probably know this, but "plenty of water coming out the exhaust" is not a measure of sufficient water, or of the colling system. The only measure of the cooling system is the temperature difference between the exhaust elbow and the engine block or oil temperature. The normal operating temperature of the block is around 80C and if the cooling system is working the exhaust elbow should be around 50C. To eliminate the cooling system as a problem, measure these temps. BTW, I cannot count how many times I have been told "plenty of water" when it was not enough water coming out.

Once the above is eliminated and the fuel system is eliminated (is the fuel pump within 8 years of age and the filters new), it is likely a sensor issue. Some model Onans have Normally Open (NO) sensors and some Onans have Normally Closed (NC) sensors. Once you determine (see below) which you have it is simple to bypass one sensor at a time by either disconnection one wire from the sensor for NO sensors, or jumping or connecting the two wires for NC sensors. Don't do this without monitoring the exhaust temperature and ensuring it does not rise above 60C.
image.png

Here is a common sensor issue (if you have the flow sensor installed). This sensor was partially clogged. Sometimes it worked and other times it shutdown the Onan. Also this sensor was found to be oriented where the debris would fall into the sensor. When it was reinstalled, it was oriented correctly (last photo):
image.png

Sensor oriented incorrectly. Sensor pipe should be turned 180 degrees:
image.png


CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
View My Training Calendar


On Wed, Aug 12, 2020 at 8:22 AM Mark Pitt <mark_pitt@...> wrote:

On my first sail trip of the season, my Onan MDKAV shuts down under load after 15 to 20 minutes.  No blinking codes.  Does not matter is the load is from the watermaker or AC.  It does not shut down from a charger load, or any load under about 15 amps.  I changed all the fuel filters but that did not help. Plenty of water coming out the exhaust.  Overheating should generate a shutdown code in any case.

Any ideas?


Mark Pitt
Sabbatical III, SM419, Rhode Island, USA


Thomas Kleman
 

Hey Mark- your post caught my eye because we are hull #422....,Bill's approach (eliminate sensors one by one) is what we do on L'ORIENT. I'm troubled by the lack of a diagnostic code, though. We've probably had 15-20 genset shutdowns in the 10 years we've owned the boat; never was there no code. Since it's really easy, at some point I'd swap out the central board (if you have one). I think this is a vital spare part to have on a SM because of how much you depend on 220 v (unless you've done a major lithium conversion).

Tom and Kirstin
SM 2K 422
Hanalei Bay, Kauia


Mark Pitt
 

Hi Tom and Kirstin,

I also have had at least a dozen shutdowns in the 17 years that I have owned Sabbatical III and in every case there was a shutdown code, including shutdowns due to a faulty sensor.  So this is a new one for me.

Having a spare central board is a good idea, although now that our circumnavigation is done, not as crucial.  I heard that they are quite expensive.  My wife and I are only summer livesboards now.

Mark Pitt
SV Sabbatical III, SM419, Rhode Island


On Aug 13, 2020, at 1:09 PM, Thomas Kleman <lorient422@...> wrote:

Hey Mark- your post caught my eye because we are hull #422....,Bill's approach (eliminate sensors one by one) is what we do on L'ORIENT. I'm troubled by the lack of a diagnostic code, though. We've probably had 15-20 genset shutdowns in the 10 years we've owned the boat; never was there no code. Since it's really easy, at some point I'd swap out the central board (if you have one). I think this is a vital spare part to have on a SM because of how much you depend on 220 v (unless you've done a major lithium conversion).

Tom and Kirstin
SM 2K 422
Hanalei Bay, Kauia


Thomas Kleman
 

Impeccable timing on your circumnav- we are stuck in Hawaii now waiting......had a new shutdown just last night. The AC water pump capacitor caused a genset shutdown at what should have been about 3 KW.....and gave me the wrong code as well. Please post when you discover the solution. I'm sure this will happen to us.

Tom and Kirstin
SM 2K 422
L'ORIENT
Hanalei Bay, Kauia


Mark Pitt
 

I installed a new flow sensor that I had in my spares.  I also replaced the impeller.  The existing impeller did not look too bad but it appeared that one vane had adhered to the impeller hub, perhaps from overheating.  I opened the cooler and found no obstructions. I also examined the hose segments from the raw water pump to the cooler and found no obstructions.

I then ran the generator under a load of 13.5 amp.  When the engine block temperature reached 103C degrees, I shut the generator off.  The exhaust elbow never topped 52C degrees.  So this appears to be a problem on the cooling side.  The cooler itself is a less than two year old "Mr. Cool" that has been in service for at least 600 hours without problem. When I put the boat away for the winter last October, there was no hint of problem.  I fully winterized it at the time.

Suggestions?

Mark Pitt
Sabbatical III, SM #419, Rhode Island, USA


Elja Röllinghoff Balu SM 222
 

He Mark



i've seen it once the Impeller didn't hold on the wave.

The level on the wave of the water pump that fixes the impeller and turns it was weared , so the impeller was in good condition but not worked because it slipped through the wave .
Good luck
Elja
SM Balu 222

Von meinem iPhone gesendet


 

Mark,

Guessing from thousands of miles away.

The shutdown is because the block is too hot. 

Normally it should be about 80C under load and warmed up. However, the exhaust elbow is at the correct temperature. My guess is that the coolant is not circulating as it should, and therefore not cooling the block. The seawater side seems to be functioning correctly, but not the coolant side. That could be a number of things including the coolant (captive) pump, a loose fan belt on the captive pump, a stuck thermostat, an obstruction somewhere in the coolant path.

I would start with the thermostat. If you do not have a spare, you can temporarily remove it until you have one. You will likely need some PermaTex-type gasket material because those gaskets usually tear.

Bill
CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
View My Training Calendar


On Fri, Aug 14, 2020 at 1:28 PM Mark Pitt <mark_pitt@...> wrote:
I installed a new flow sensor that I had in my spares.  I also replaced the impeller.  The existing impeller did not look too bad but it appeared that one vane had adhered to the impeller hub, perhaps from overheating.  I opened the cooler and found no obstructions. I also examined the hose segments from the raw water pump to the cooler and found no obstructions.

I then ran the generator under a load of 13.5 amp.  When the engine block temperature reached 103C degrees, I shut the generator off.  The exhaust elbow never topped 52C degrees.  So this appears to be a problem on the cooling side.  The cooler itself is a less than two year old "Mr. Cool" that has been in service for at least 600 hours without problem. When I put the boat away for the winter last October, there was no hint of problem.  I fully winterized it at the time.

Suggestions?

Mark Pitt
Sabbatical III, SM #419, Rhode Island, USA


Mark Pitt
 

 After replacing the thermostat, water sensor, fan belt, coolant, and raw water pump, it turns out the problem was carbon buildup in the exhaust manifold.  That’s been cleaned out and a new exhaust elbow added and all seems good now.  Thanks to all for their suggestions.

Mark Pitt
Sabbatical III,SM#419
Nantucket


Thomas Peacock
 

Hi Mark,

I was actually going to suggest that you look at the exhaust manifold, but didn’t want to look dumb. However, our problem wasn’t that it would shut down, but that it would not start. Many $$$ later, a good mechanic looked there and found the culprit.

In addition, I would have thought that the exhaust temperature would have risen and tripped the generator; but not all Onans are the same, I don’t think we have an exhaust temperature monitor, just a water temp.

I should add that the exhaust manifold carbon buildup is a common problem; it results from the generator being run at relatively low power demand levels, never at high enough fuel consumption (the RPM are constant) to burn out the carbon.

Everyone who has an Onan should be aware of this, and keep an eye on the build-up.  Ours was so far gone that we had to replace the manifold, cleaning was not an option.

Tom Peacock
SM 240 Aletes
Chesapeake Bay

On Aug 21, 2020, at 5:48 PM, Mark Pitt <mark_pitt@...> wrote:

 After replacing the thermostat, water sensor, fan belt, coolant, and raw water pump, it turns out the problem was carbon buildup in the exhaust manifold.  That’s been cleaned out and a new exhaust elbow added and all seems good now.  Thanks to all for their suggestions.

Mark Pitt
Sabbatical III,SM#419
Nantucket


--
Tom Peacock
SM 240 Aletes
Chesapeake Bay


 

Mark,

I think I should have suggested that because the exhaust elbow was at the correct temperature, but the engine overheating. 

I think if I added the following  to the top of the check list you would have found it earlier:

"Remove the exhaust elbow and inspect the junction of the elbow with the manifold. If you see carbon buildup, remove the manifold and clean or replace both the manifold and the elbow."

Agree?

Best,

CW Bill Rouse 
Amel Owners Yacht School
+1 832-380-4970 | brouse@...
720 Winnie, Galveston Island, Texas 77550 
www.AmelOwnersYachtSchool.com 
Yacht School Calendar: www.preparetocastoff.blogspot.com/p/calendar.html


   


On Fri, Aug 21, 2020, 5:19 PM Thomas Peacock <peacock8491@...> wrote:
Hi Mark,

I was actually going to suggest that you look at the exhaust manifold, but didn’t want to look dumb. However, our problem wasn’t that it would shut down, but that it would not start. Many $$$ later, a good mechanic looked there and found the culprit.

In addition, I would have thought that the exhaust temperature would have risen and tripped the generator; but not all Onans are the same, I don’t think we have an exhaust temperature monitor, just a water temp.

I should add that the exhaust manifold carbon buildup is a common problem; it results from the generator being run at relatively low power demand levels, never at high enough fuel consumption (the RPM are constant) to burn out the carbon.

Everyone who has an Onan should be aware of this, and keep an eye on the build-up.  Ours was so far gone that we had to replace the manifold, cleaning was not an option.

Tom Peacock
SM 240 Aletes
Chesapeake Bay

On Aug 21, 2020, at 5:48 PM, Mark Pitt <mark_pitt@...> wrote:

 After replacing the thermostat, water sensor, fan belt, coolant, and raw water pump, it turns out the problem was carbon buildup in the exhaust manifold.  That’s been cleaned out and a new exhaust elbow added and all seems good now.  Thanks to all for their suggestions.

Mark Pitt
Sabbatical III,SM#419
Nantucket


--
Tom Peacock
SM 240 Aletes
Chesapeake Bay