Onan Generator

[Hurricane]

I've done it - mended something that wasn't broken.
I know I shouldn't have but it seemed a good idea at the time.

My Onan generator is due a service so I thought I would change the impeller and do a full service later in the summer when I have more time.

After changing the impeller water doesn't seem to be flowing.
So, is it my work changing the impeller or is it something else.
The heat exchanger is the same one from new (10 years) but I have a spare that I should have changed before now.

It is too hot at the moment to strip down.
I thought I would start at the impeller and see if I've done something wrong there.

But what do people think - is it likely to be something else - the heat exchanger for example?

 

[Portofino]

FInd a way of priming the water - i.e. Refilling it before start
Or your face plate is allowing air in
Assuming it's your 1st go @ this ?

 

[JerryC]

My golden rule before stripping anything down is to run it first and make sure it performs properly.

 

[Hurricane]

FInd a way of priming the water - i.e. Refilling it before start
Or your face plate is allowing air in
Assuming it's your 1st go @ this ?

This is not my first go at this.
I have just had a good look at the heat exchanger and it looks OK so I'm going to strip the impeller down again tonight.

 

[Hurricane]

My golden rule before stripping anything down is to run it first and make sure it performs properly.

Yea yea - thats what I usually do - just didn't this time!!
I've changed the impeller before without any problems so it should have been ok.

 

[Hurricane]

So
I've stripped and reassembled the pump - even put the old (reasonably good) impeller back in.
Still no water movement.

I checked that the raw water isn't blocked - at the strainer - all OK.

So, I had a look in my shed and found a short length of rubber tube that a good friend gave me at the end of last year - he knows who he is.
And I attached it to the outlet of the pump and ran the generator.
The water from the pump flows beautifully - filling a bucket in seconds.

So, it looks like tomorrow we will be replacing the heat exchanger.

Unless someone can come up with any other ideas?????????

Exhaust system????

Any ideas welcome.

 

[MapisM]

Any ideas welcome.

I'm not hoping to win any Nobel prize for this idea, but how can you be sure that the raw water isn't flowing regularly? Did you have any genset alarm going off?
I'm asking because it wouldn't be the first boat (among those with submerged genset raw water outlet, as I suppose JW also is) where no water movement was perceivable through the transparent lid of the water strainer, but actually everything was working just fine....
Well, I wish you that this is the case, anyway! :encouragement:

 

[jfm]

There's a pressure transducer that shuts the engine down if no raw water pressure, so if engine runs the raw water is flowing.

 

[Hurricane]

I'm not hoping to win any Nobel prize for this idea, but how can you be sure that the raw water isn't flowing regularly? Did you have any genset alarm going off?
I'm asking because it wouldn't be the first boat (among those with submerged genset raw water outlet, as I suppose JW also is) where no water movement was perceivable through the transparent lid of the water strainer, but actually everything was working just fine....
Well, I wish you that this is the case, anyway! :encouragement:

I couldn't see any flow in the raw water strainer and it didn't feel right.
After running for a few minutes, the pump was getting very hot.

There's a pressure transducer that shuts the engine down if no raw water pressure, so if engine runs the raw water is flowing.

Yes - I can see that switch.
When it was running, I tapped it and the genset shut down as though the pressure switch was sticking.
I have a new pressure switch that came with the new heat exchanger.

My thoughts are that the flow is being significantly reduced.
Do you think that replacing the heat exchanger will fix my problems?

 

[vas]

Isn't it easier to check the elbow first Mike?

V

 

[jfm]

Yep I think change the heat ex hurricane. They are typically 7-8 years life anyway.

I realise it is hard to get to on the 17.5 kva model. A lot easier on the 22.5.

 

[Hurricane]

Yep I think change the heat ex hurricane. They are typically 7-8 years life anyway.

I realise it is hard to get to on the 17.5 kva model. A lot easier on the 22.5.

Actually, thinking about it (my last regarding the pressure switch).
I think the genset turning off as I hit the pressure switch is just a coincidence.
The error message reported at that time was "high exhaust temp" - i.e. not enough raw water flow.
And a pressure switch doesn't measure flow - just pressure.

Covers are off now - the next big job is draining the coolant inside the heat exchanger - there isn't room to remove the drain plug.
So, I'm planning on part removing the heat exchanger whilst still leaving the hoses attached.
Other than that, we will just have to prepare for a rush of coolant.
I have some notes that ARE sent me when I bought the new heat exchanger - his notes make it sound easy!!!

 

[Hurricane]

Problem solved!!

The heat exchanger was "kind of" ok but the raw water pipe connections to and from it were blocked with calcium deposit.
In fact we had to remove the tubes as well and flush out.
The new heat exchanger is installed and all is working.
I will take time later and see if the old one can be cleaned up as a spare - a good acid wash might clean the tubes inside the heat exchanger.
A decision to keep it will be make later.
I have taken some pics of the blocked pipes - I will post them later - this thread might be useful if anyone else has this problem in the future.

Thanks to everyone.
Even if your comments weren't the solution, the moral support is invaluable.

Plan is now for a short early season cruise to Mallorca.
Just waiting to a weather window and our first stop will probably be Santa Ponsa - Tuesday, Wednesday or Thursday - depending on conditions.
The plan is on anchor as usual so we needed that generator working.

 

[Pinnacle]

Mike

Delighted you have solved the problem. Enjoy your trip to Mallorca!��

 

[Zing]

Here's a coincidence. I am sorting out a similar problem on my 17.5Kw Onan. First I couldn't start it. It turned out to be a failed control voltage from the AVR. Then seemingly coincidentally after I got it going by by-passing the AVR I had a boil over. In my case the impeller shredded itself. Bits everywhere, also blocking the heat exchanger. A solid day of grief.

By the way, I looked for the pressure sensor mentioned above on the raw circuit and my set doesn't have one. At least, I can't find it anywhere. A 2002 model. Maybe they were introduced later.

By the way, does anyone know who rebuilds/repairs Onan AVR boards? They cost a rather heady £800 new.

 

[Hurricane]

For the record, our genset is an MDKBR - Spec B - 17.5KVA.

After removing the casing, the hardest part of changing the heat exchanger was removing the old coolant.
There are drain points on the underside of the heat exchanger but they are impossible to get to.
We first drained the coolant from the main engine drain point and then cracked the large hose on the side of the heat exchanger.
Careful placement of rags stopped the coolant from flowing under the engine.
I have been dreading this job - I thought that the hoses would be stuck fast but, in fact, the hoses came apart easily.
The rest of the job was fairly straight forward.
Having just replaced the coolant on the main engines, I had plenty of new coolant left over for this job.

These are the pics of the old heat exchanger - you can see that it was completely blocked.

 

[mcanderson]

If it helps at all, I think your teak looks brilliant. What do you use to keep it in that shape?

 

[Zing]

That’s quite a blockage.

 

[Zing]

Does anyone have a good source for Onan parts? It seems I need a new stop solenoid also. It was failing and shuddering in and out before the AVR failed.

 

[jrudge]

Problem solved!!

The heat exchanger was "kind of" ok but the raw water pipe connections to and from it were blocked with calcium deposit.
In fact we had to remove the tubes as well and flush out.
The new heat exchanger is installed and all is working.
I will take time later and see if the old one can be cleaned up as a spare - a good acid wash might clean the tubes inside the heat exchanger.
A decision to keep it will be make later.
I have taken some pics of the blocked pipes - I will post them later - this thread might be useful if anyone else has this problem in the future.

Thanks to everyone.
Even if your comments weren't the solution, the moral support is invaluable.

Plan is now for a short early season cruise to Mallorca.
Just waiting to a weather window and our first stop will probably be Santa Ponsa - Tuesday, Wednesday or Thursday - depending on conditions.
The plan is on anchor as usual so we needed that generator working.

In andraxt so do shout if you are here. I need my exchanger stripping as well !!