Re: Onan MDKAV vented loop

Danny and Yvonne SIMMS

Hi Paul, I had the same issue with valves needing replacement. The cause was in the exhaust elbow where the salt water cooling line entered the elbow. I dont know if the elbow on my Kubota was original Amel install. A previous owner replaced the Onan with another genset which uses the same Kubota power unit. The elbow  is of stainless steel and the water enters through a tube on top of the elbow. The elbow looked fine but I didn't realise that the tube was supposed to continue internally an inch or two to carry the discharge away. This internal part had corroded off. In my innocence I replaced the valves and happily carried on. In an incredibly short time the valves had rotted again. I then looked further and took advice. When a diesel engine stops it give a little cough sucking exhaust gasses back. Because that tube had corroded off that cough carried salt water back into the cylinder head. I replaced the elbow and some years later all is still well. My venting loop is as yours is. I would suggest you check your exhaust elbow.
Kind Regards
SM 299
Ocean Pearl

On 27/10/2022 04:09 Paul via <paulguenette@...> wrote:

Thanks Bill,

I have been told by three mechanics and two surveyors that:

1. The vented loop should be vertical not horizontal.

2. The way the vented loop is plumbed into the exhaust hose is not a good idea.

All five said the way it is set up can potentially lead to problems with water working its way back to the engine causing mechanical problems or worse.

We just spent a few days cleaning out the exhaust elbow, exhaust manifold and replacing a two valves, (that prevented the Kubota from working). It looked like there was slight water or moisture causing corrosion in the area of the valves. The mechanic who was helping me said he believed the current vented loop set up is most likely what caused the issue. We now have the generator working again, but I have been strongly advised to modify the current vented loop system.

1. Change the vented loop so it is vertical, (not horizontal).

2. Remove the drain of vented loop from where it is now, (plumbed into the Onan wet exhaust hose), and move it to a place like or even beside the one for the main engine.

With the upmost respect to the designers of my Amel,  I am wondering if there have been any problems on other Amels with the way the original vented loop system has been set up on their Onan-Kubota gen-sets ?

Has anyone changed or modified the vented loop coming of the the Onan-Kubota gen-set ?

Thank you for your time.

SM - 444
Comox, BC, Canada

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