Coolant loss - running out of ideas...

[Still Grinning]

Another technical one for the East Coast collective....

My Nanni 3.75HE (a 21HP Kubota based engine) is losing coolant, but I know not where.

A little history:

• The engine has done about 2,300 hours and runs beautifully - starts first time, no smoke, smooth, plenty of power, etc etc.;
• We had an overheat last season due to a hose blowing off (not secured properly after replacement... no names, no pack drill...), but engine ran fine again after that and was good all year, with no coolant loss thereafter;
• I replaced the Heat Exchanger O-rings over last winter, and all seemed fine, at first. But after the first longer run (just 2 hours), I missed my usual daily fluid check (I know, I know...), and on the return we overheated again. After adding coolant all seemed well once more, except now I was tracking coolant levels religiously, and could see we were continuing to lose excess amounts (perhaps 0.5L every 1 - 2 hrs):
• No visible leaks anywhere - over the course of several weeks I added over 2L of coolant, which didn't show up anywhere in the boat.

So, given the above, we considered several options - Heat exchanger, calorifier, head gasket.
The Heat Exchanger itself was brand new 2 years ago, and the new O-rings are only to seal the end caps, so should not be cause for concern, but I'll come back to this presently.
Calorifier - if that amount of water is going into the Calroifier, where is it going? i.e. You can't put 0.5L into the calorifier without it coming out, and we are not seeing that quantity coming out of the PRV.. We generally don't run the tap whilst we are motoring, so I can't see this being a possible route.

Consequently, we decided that we should check the head gasket, especially given we had now had 2 overheats. Head was pulled and we found no evidence of cross leakage. The head gasket was showing some evidence of blowing between cylinders (possibly only causing an issue when the engine got over warm, when it did start to run a little lumpily). Head was pressure tested, all ok and given a very light skim. We took the heat exchanger for pressure testing too, and that also passed with flying colours.

Engine re-assembled with new head gasket and all running beautifuly again..... except.... still losing coolant. Grrr......

Where does that leave us? Given all of the above I can only see two possibilities:
(i) Heat exchanger - but it did pass the pressure test
or
(ii) Calorifier - but my comment above still stands?

I guess I should bypass the calorifier, and do some more running, though of course now my boat is due out of the water on Friday. If this goes into next year I run the risk of ruining another season, having not dared a long trip this year (wind always seems to be wrong direction, or non-exiatant, so I want the ability to motor if needed).

Unless anyone has any other suggestions?

I really am at my wit's end and this is certainly making the stress / reward equation for my boating out of balance the 'wrong' way.

All help gratefully received!

 

[Plum]

Another technical one for the East Coast collective....

My Nanni 3.75HE (a 21HP Kubota based engine) is losing coolant, but I know not where.

A little history:

• The engine has done about 2,300 hours and runs beautifully - starts first time, no smoke, smooth, plenty of power, etc etc.;
• We had an overheat last season due to a hose blowing off (not secured properly after replacement... no names, no pack drill...), but engine ran fine again after that and was good all year, with no coolant loss thereafter;
• I replaced the Heat Exchanger O-rings over last winter, and all seemed fine, at first. But after the first longer run (just 2 hours), I missed my usual daily fluid check (I know, I know...), and on the return we overheated again. After adding coolant all seemed well once more, except now I was tracking coolant levels religiously, and could see we were continuing to lose excess amounts (perhaps 0.5L every 1 - 2 hrs):
• No visible leaks anywhere - over the course of several weeks I added over 2L of coolant, which didn't show up anywhere in the boat.

So, given the above, we considered several options - Heat exchanger, calorifier, head gasket.
The Heat Exchanger itself was brand new 2 years ago, and the new O-rings are only to seal the end caps, so should not be cause for concern, but I'll come back to this presently.
Calorifier - if that amount of water is going into the Calroifier, where is it going? i.e. You can't put 0.5L into the calorifier without it coming out, and we are not seeing that quantity coming out of the PRV.. We generally don't run the tap whilst we are motoring, so I can't see this being a possible route.

Consequently, we decided that we should check the head gasket, especially given we had now had 2 overheats. Head was pulled and we found no evidence of cross leakage. The head gasket was showing some evidence of blowing between cylinders (possibly only causing an issue when the engine got over warm, when it did start to run a little lumpily). Head was pressure tested, all ok and given a very light skim. We took the heat exchanger for pressure testing too, and that also passed with flying colours.

Engine re-assembled with new head gasket and all running beautifuly again..... except.... still losing coolant. Grrr......

Where does that leave us? Given all of the above I can only see two possibilities:
(i) Heat exchanger - but it did pass the pressure test
or
(ii) Calorifier - but my comment above still stands?

I guess I should bypass the calorifier, and do some more running, though of course now my boat is due out of the water on Friday. If this goes into next year I run the risk of ruining another season, having not dared a long trip this year (wind always seems to be wrong direction, or non-exiatant, so I want the ability to motor if needed).

Unless anyone has any other suggestions?

I really am at my wit's end and this is certainly making the stress / reward equation for my boating out of balance the 'wrong' way.

All help gratefully received!

The most likely culprits are those heat exchanger end cap O rings not sealing correctly allowing coolant under pressure to leak into the seawater system and then out of your exhaust, which is why you cannot find any evidence of coolant that has escaped. I expect, based on experience of other engiines, those O rings perform two functions. They stop any leakage into the engine compartment and also seal the coolant from the seawater. It is the later function that I expect is at fault. How exactly did you do the pressure test? Even a pressure test on a cold engine may not reveal a leak when everything is hot.

 

[Plum]

The most likely culprits are those heat exchanger end cap O rings not sealing correctly allowing coolant under pressure to leak into the seawater system and then out of your exhaust, which is why you cannot find any evidence of coolant that has escaped. I expect, based on experience of other engiines, those O rings perform two functions. They stop any leakage into the engine compartment and also seal the coolant from the seawater. It is the later function that I expect is at fault. How exactly did you do the pressure test? Even a pressure test on a cold engine may not reveal a leak when everything is hot.

Also, if you go to this page and scroll down a long way you will see details of a poorly sealling heat exchanger O ring
December 2018

 

[mullet]

Have you pressure tested the engine side of the coolant system (as opposed to just the heat exchanger)? A basic kit (expanding bung to go in neck of the coolant filler) is pretty inexpensive. If you can’t find the missing coolant anywhere on the boat I’d suspect it might be finding its way into the raw water side, my first place to check would be the seals around the heat exchanger stack. A pressure test might also help you find a pinhole leak on a hose that would be harder to spot with a running engine.

 

[Boater Sam]

Leaking coils in calorifiers are extremely rare.
As the problem started after you changed the o rings on the end caps, I suspect that is where the problem is. They not only seal the caps but seal the stack from the raw sea water system.

 

[DanTribe]

My general rule when things go wrong is to check the last thing I "fixed".
If it was OK before, the chances are that something was disturbed during the repair. so O rings would be my first suspect.
If it ain't broke, fix it until it is.

 

[rogerthebodger]

When I had a loss of coolant that I could not find I did a pressure test on the cylinders and inspected the possible outlets from the cylinder.
Head Gasket
Ring seals
air leaking out of the heat exchanger and inlet and /or exhaust valves. This gave me idea of where any water or gasses were leaking from.

 

[38mess]

Heat exchanger o rings I would suggest as above

 

[Still Grinning]

I forgot to mention that I focused on the Head Gasket as I did a leak detection test (exhaust gasses in the coolant), which was positive. I feel the head gasket needed doing anyway (probably damaged by the 2 overheats).

From the above I think you have all confirmed my thoughts - i.e. I messed up the O-Ring change somewhow. It is a pig of a job (most of the skin has grown back on my knuckles since I did it in March....), which is probably why I hoped / was determined, to find another cause!

However, I agree with the logic - it was OK before I 'fixed' it, it isn't now, so check what I fixed..... Will try and get to that this week.

Thanks for everyone's input - Two more numpty points for me by the looks of things. I will update when I know more.

 

[Plum]

I forgot to mention that I focused on the Head Gasket as I did a leak detection test (exhaust gasses in the coolant), which was positive. I feel the head gasket needed doing anyway (probably damaged by the 2 overheats).

From the above I think you have all confirmed my thoughts - i.e. I messed up the O-Ring change somewhow. It is a pig of a job (most of the skin has grown back on my knuckles since I did it in March....), which is probably why I hoped / was determined, to find another cause!

However, I agree with the logic - it was OK before I 'fixed' it, it isn't now, so check what I fixed..... Will try and get to that this week.

Thanks for everyone's input - Two more numpty points for me by the looks of things. I will update when I know more.

I recommend:-
1) remove the whole heat exchanger from the engine and take it home to a workbench. It is then so much easier to achieve a good end cap O-ring fitting than while still on the engine.
2) while at home and once the end caps are in place, do a pressure test on the coolant side with the whole heat exchanger completely submerged in a tank of water so the can both monitor how long the pressure is held for and also watch for escaping bubbles. I did my pressure test to 15psi but check what it says for yours in the workshop manual (you could also repeat with the standard pressure cap to ensure that leaks at the specified pressure).
3) while you are at it, unless you have already done it recently, check and clean out your exhaust water injection bend.

 

[Still Grinning]

Thanks Plum.

But...... It is only possible to get the Heat Exchanger off the engine if I either (i) take the cylinder head off the engine as well, or (ii) take the engine out of the boat, both of which I have done in the last 2 years, neither of which I wish to do again if I can avoid it!!! (It's actually quicker to take the engine out than get the cylinder head off, as it happens, but they are the last and last but one, resorts )

The heat exchanger was new in March 2023, together with the water injection elbow, so I think we are good in that area, at least.

 

[rogerthebodger]

As Plum says do a pressure test and use a squeeze bottle with washing up liquid to look for leaks.

Once you gave found the leaks you can then decide how to proceed.

 

[Slipstream 34]

We had an issue with coolant loss this year on a Perkins 4108. Eventually tracked it down to the coolant circulation pump. There was a small amount of play in the bearings allowing the coolant to leak past the seals. The lost coolant evaporated in the warm engine bay so there was no evidence of where the coolant was leaking from. A new pump cured the problem.

 

[Beneteau381]

Thanks Plum.

But...... It is only possible to get the Heat Exchanger off the engine if I either (i) take the cylinder head off the engine as well, or (ii) take the engine out of the boat, both of which I have done in the last 2 years, neither of which I wish to do again if I can avoid it!!! (It's actually quicker to take the engine out than get the cylinder head off, as it happens, but they are the last and last but one, resorts )

The heat exchanger was new in March 2023, together with the water injection elbow, so I think we are good in that area, at least.

Double nut the studs and remove them?

 

[rogerthebodger]

how to remove the heat exchanger from a nanni 3.75he - Bing

 

[MontyMariner]

I replaced the Heat Exchanger O-rings over last winter,

First principals of fault finding - What has changed?

 

[Jim@sea]

Although this might not be the problem. I had a Zetor Tractor and one day while running the engine lost all its water and nearly seized up, what had happened was a small hole had appeared in the cylinder bore so every time the piston went down it would suck some water out of the cylinder jacket until there was no more water in the engine block.

 

[Still Grinning]

Double nut the studs and remove them?

I can undo the studs, but there is not enough clearance between the side of the engine and the wall to get them out - hence engine out or cylinder head off!