Onan Generator Heat Exchanger Cleaning

jrudge

jrudge

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The gen exhaust is steaming a bit and the flow seems slow.

I have checked the impeller and the raw water filter - all fine.

As such I assume that the exchanger is blocked either with weed, old impeller or limescale.

I assume that i remove (one?) end cap and rod it through with a piece of coat hanger?

I have tried a bit of acid but I have no way of recirculating it and the exchanger looks accessible. The hoses to remove and circulate are tricky to get to and if it is old impeller it wont work anyway .

Questions

1. do i need new seals or are they just rubber and re-usable ?
2. do i need to remove both ends ? I would assume any grid just gets washed out
3. if limescale is this usually sludgy solid or solid solid? I only ask as if solid in the tube ( I dont want to remove the whole thing) i assume getting a rod through it is tricky .


Many thanks

Jeremy
 
What’s the exact recent history of events ps .
And by who ?

If you can remove the HE , take off both caps to check for debris and soak the stack in acid ( small kitchen bowl ? )
Then that’s belt n braces
You can buy a set of wire pipe cleaners 2-6 mm dia
 
Last edited:
jrudge said:
The gen exhaust is steaming a bit and the flow seems slow.

I have checked the impeller and the raw water filter - all fine.

As such I assume that the exchanger is blocked either with weed, old impeller or limescale.

I assume that i remove (one?) end cap and rod it through with a piece of coat hanger?

I have tried a bit of acid but I have no way of recirculating it and the exchanger looks accessible. The hoses to remove and circulate are tricky to get to and if it is old impeller it wont work anyway .

Questions

1. do i need new seals or are they just rubber and re-usable ?
2. do i need to remove both ends ? I would assume any grid just gets washed out
3. if limescale is this usually sludgy solid or solid solid? I only ask as if solid in the tube ( I dont want to remove the whole thing) i assume getting a rod through it is tricky .


Many thanks

Jeremy
Click to expand...
jeremy some onan have the heat ex vertical at the front (mine do!)'but some have it tucked at the back horizontally and much less accessible. I've fiddled with these zillions of times and invariably the old impeller places are at the top/inlet of the heat ex and have not gone inside the tubes. Often they are in the end of the rubber feed hose that feeds into the heat ex seawater inlet. You therefore just remove the one top bolt in the inlet end cap of the heat ex, and the inlet hose, and you'll get to all the impeller bits. Rubber gasket for cap of heat ex is reusable several times if you don't have a new one to hand. .
If access is tricky just fit a whole new heat ex while you're doing the job. They last 7 years if you don't flush with freshwater i.e. If seawater sits in there all winter. So you might be due. They're small by heat ex standards and not massively expensive though obviously there is some "boat premium" in the price.
I've never rodded one through; never needed to.
 
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jfm said:
jeremy some onan have the heat ex vertical at the front (mine do!)'but some have it tucked at the back horizontally and much less accessible. I've fiddled with these zillions of times and invariably the old impeller places are at the top/inlet of the heat ex and have not gone inside the tubes. Often they are in the end of the rubber feed hose that feeds into the heat ex seawater inlet. You therefore just remove the one top bolt in the inlet end cap of the heat ex, and the inlet hose, and you'll get to all the impeller bits. Rubber gasket for cap of heat ex is reusable several times if you don't have a new one to hand. .
If access is tricky just fit a whole new heat ex while you're doing the job. They last 7 years if you don't flush with freshwater i.e. If seawater sits in there all winter. So you might be due. They're small by heat ex standards and not massively expensive though obviously there is some "boat premium" in the price.
I've never rodded one through; never needed to.
Click to expand...

Thank John

I have a horizontal one at the bottom right of the unit as you look at it. Accessibility is - for a boat - I would say average. Ie a pig but not impossible.

Last time the impeller went i had someone open the exchanger and remove the bits. I did not look what they did and for all I know they may just have accessed the top of the tube as you say.

I will take the end off and see what lies beneath!
 
jrudge said:
Thank John

I have a horizontal one at the bottom right of the unit as you look at it. Accessibility is - for a boat - I would say average. Ie a pig but not impossible.

Last time the impeller went i had someone open the exchanger and remove the bits. I did not look what they did and for all I know they may just have accessed the top of the tube as you say.

I will take the end off and see what lies beneath!
Click to expand...

Get yourself a spare & swap it over & service it at your leisure. I do this, i have the 11Kw MDKAZ which has the horizontal one low down. Clamp the colant hoses & you wont lose much.

I only clean mine using Rydlme, rodding not easy as several tubes are hard to get at due to the design. Not worth risking the damage.

I find it blocks more the less hours I do each year & worse at the anode end. Probably swap mine over every 3 years & take it home to clean & paint.
 
Thanks

Mine seems to be 130−5006−02 which is not listed.

Sent them a mail. They are $350 in the USA.

I would rather check it out before buying one as if nothing else it will be a pig to remove!
 
jrudge said:
Thanks

Mine seems to be 130−5006−02 which is not listed.

Sent them a mail. They are $350 in the USA.

I would rather check it out before buying one as if nothing else it will be a pig to remove!
Click to expand...

You could buy a small submersible bilge pump some hose & circulate Rydlme. I do this for my stabiliser oil heat exchanger. Cheaper for sure.

Worth removing the end caps to have a look i agree. Put them back as you take them off as the gasket does hold the indentations of the metalwork. I agree with John you can get a couple or so removals. Again worth holding spare end cap kits.
 
jrudge said:
The gen exhaust is steaming a bit and the flow seems slow.

I have checked the impeller and the raw water filter - all fine.

As such I assume that the exchanger is blocked either with weed, old impeller or limescale.

I assume that i remove (one?) end cap and rod it through with a piece of coat hanger?

I have tried a bit of acid but I have no way of recirculating it and the exchanger looks accessible. The hoses to remove and circulate are tricky to get to and if it is old impeller it wont work anyway .

Questions

1. do i need new seals or are they just rubber and re-usable ?
2. do i need to remove both ends ? I would assume any grid just gets washed out
3. if limescale is this usually sludgy solid or solid solid? I only ask as if solid in the tube ( I dont want to remove the whole thing) i assume getting a rod through it is tricky .


Many thanks

Jeremy
Click to expand...

Hi Jeremy,

The heat exchanger is not to bad to rod out, if i remember correctly the heat exchanger is twin pass ie there is a dividing baffle in the rear of the exchanger, so you need to take both covers off.

As John said the end cap rubber seals are reusable a couple of times.

I would also check the injection elbow as these can block up with corrosion or an old piece of anode.

Let me know if you need an exchanger or injection elbow.

Regards Anthony
 
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