gas pressure in cooling system

[DBA Forum (B) - Andrew Alexander]

I have a bit of a problem which has so far flummoxed two engineers and a very frustrated boat owner. Does anyone have any suggestions/diagnosis that might help?

I have a 55HP Isuzu motor which is cooled by a skin tank which is pushing a 60ft by 10ft wide beam. After a few hours use in seems to generate a significant amount of gas in the system which pressurises the skin tank. Before every trip I have to bleed off this gas to stop it building up. After 6 hours or so it blows all the water out of the radiator cap I assume to relieve this build up of pressure? Prior to all this it happily runs at 80 degrees with no overheating issues.
We obviously thought head gasket but no oil in water or water in oil. If I stop it from blowing its top then it uses no water it also does not use any oil .We have checked the gases coming out of the rad cap and it is not carbon dioxide.
I suspect that the skin tank is not man enough for the engine and this is to be rectified next month with extra cooling. Because I suspect this I only run at low revs and do nothing to create an overheating issue.
So far I have only used the boat on the K and A canal and for the last three months on the Thames. The original owners only used it on the K and A where it never gets above tick over. I had noticed this pressure issue before I moved onto the Thames so the change is not the issue.
Can anyone think where all this gas is coming from as it is not from the engine?

[DBA Forum (B) - Harold Flescher]

My guess is that somewhere there is air in the system that isn’t yet bleed out. Look for the highest point in the system, and that includes your calorifier. Air hides in the highest part of the system, and there needs to be a bleed at exactly that point. The coolant doesn’t flow fast enough through the system to push the air out, so it just lives there forever (in barge terms).

H
Harold L. Flescher



On Aug 18, 2014, at 11:33 AM, DBA Forum (B) - Andrew Alexander <dbabarges-pvYRptiajiAdnm+***@public.gmane.org> wrote:
I have a bit of a problem which has so far flummoxed two engineers and a very frustrated boat owner. Does anyone have any suggestions/diagnosis that might help?

I have a 55HP Isuzu motor which is cooled by a skin tank which is pushing a 60ft by 10ft wide beam. After a few hours use in seems to generate a significant amount of gas in the system which pressurises the skin tank. Before every trip I have to bleed off this gas to stop it building up. After 6 hours or so it blows all the water out of the radiator cap I assume to relieve this build up of pressure? Prior to all this it happily runs at 80 degrees with no overheating issues.
We obviously thought head gasket but no oil in water or water in oil. If I stop it from blowing its top then it uses no water it also does not use any oil .We have checked the gases coming out of the rad cap and it is not carbon dioxide.
I suspect that the skin tank is not man enough for the engine and this is to be rectified next month with extra cooling. Because I suspect this I only run at low revs and do nothing to create an overheating issue.
So far I have only used the boat on the K and A canal and for the last three months on the Thames. The original owners only used it on the K and A where it never gets above tick over. I had noticed this pressure issue before I moved onto the Thames so the change is not the issue.
Can anyone think where all this gas is coming from as it is not from the engine?

[DBA Forum (B) - Andrew Alexander]

Harold Thank you but I get masses of air 15 to 20 seconds worth after every few hours of running . The highest point in the system is my header tank . We have also checked the calorifier but all appears in order there.

[DBA Forum (B) - David Beaumont]

sounds like your first suspicion - leaking head gasket. Leaks can occur with no obvious water in oil/oil in water. That much gas under pressure is likely to be mechanical in source not chemical. Assuming it is a dry exhaust, is there any abnormal steam from the exhaust?

How are you checking the gas is not C0[sub]2[/sub]? Any lead up to the problem eg overheat or strenuous use?

If head gasket try tightening the head bolts to spec and beyond by as much as you dare. Otherwise head off and new gasket.

David

[DBA Forum (B) - John Booker]

Andrew,

We had a similar problem with our new Piper barge 4 years ago. It was
caused by air in the cooling system. Although the header tank appeared
to be the highest point it was attached to the engine. The problem was
solved by tapping a hole at an adjacent point which was also high in the
cooling circuit and putting in a remote header tank which was much
higher than the engine. That allowed the trapped air to find it's way
out of the engine and into the header tank.
Don't mess around with the head bolts etc, if the engine runs at
tickover OK for several hours it's not the head gasket.
Your problem is the inability of your cooling circuit to transfer the
heat required when running under greater load. The skin tank is probably
ok for size but the circulation through it may be wrong if baffles etc
are not installed correctly, so that there are big dead spots allowing
the hot water to bypass much of the tank. Look for air locks first
though, the second is the sort of error that a professional boat builder
would be unlikely to make. An amateur boat builder would be another
matter of course.......
Regards
John Booker

Post by DBA Forum (B) - Andrew Alexander
I have a bit of a problem which has so far flummoxed two engineers and a very frustrated boat owner. Does anyone have any suggestions/diagnosis that might help?
I have a 55HP Isuzu motor which is cooled by a skin tank which is pushing a 60ft by 10ft wide beam. After a few hours use in seems to generate a significant amount of gas in the system which pressurises the skin tank. Before every trip I have to bleed off this gas to stop it building up. After 6 hours or so it blows all the water out of the radiator cap I assume to relieve this build up of pressure? Prior to all this it happily runs at 80 degrees with no overheating issues.
We obviously thought head gasket but no oil in water or water in oil. If I stop it from blowing its top then it uses no water it also does not use any oil .We have checked the gases coming out of the rad cap and it is not carbon dioxide.
I suspect that the skin tank is not man enough for the engine and this is to be rectified next month with extra cooling. Because I suspect this I only run at low revs and do nothing to create an overheating issue.
So far I have only used the boat on the K and A canal and for the last three months on the Thames. The original owners only used it on the K and A where it never gets above tick over. I had noticed this pressure issue before I moved onto the Thames so the change is not the issue.
Can anyone think where all this gas is coming from as it is not from the engine?

[DBA Forum (B) - Richard Cooper]

Well, First thoughts are cyl. head as exhaust gas blowing at high pressure into a waterway through a crack or head gasket seems likely but if the engine is recent that makes it less likely, does the engine have a water cooled exhaust manifold? if there is a pinhole within that then hot and high pressure exhaust gas may just be blowing through into the water. If the engine does not overheat then apparently the skin tank is doing its job, Does it get v. hot to the touch all over? Is there water in the exhaust?
How have you checked the gas for CO2? is it by using a CO2 alarm in the expelled gas ? I don`t know if a CO2 alarm would go off in exhaust gas. if you take the rad cap off and run the engine are there bubbles in it? Must be a reason but it may take some finding .

[DBA Forum (B) - Harold Flescher]

An interesting problem

H
Harold L. Flescher8124 159th Court NorthPalm Beach Gardens, FL 33418561-741-4804 Land/Fax [phone] Cellh.flescher-***@public.gmane.org___________Find out what technical opportunities IEEE offers - Try the IEEE Technology Navigator! http://technav.ieee.org


On Aug 18, 2014, at 12:02 PM, DBA Forum (B) - Andrew Alexander <dbabarges-pvYRptiajiAdnm+***@public.gmane.org> wrote:
Harold Thank you but I get masses of air 15 to 20 seconds worth after every few hours of running . The highest point in the system is my header tank . We have also checked the calorifier but all appears in order there.

[DBA Forum (B) - David Beaumont]

I don't get how air in the cooling system could produce the gas unless it is actually steam caused by water boiling at the hotspots. A boiling cooling system is quite recognisable though. Exhaust gas from a manifold pinhole is certainly a possibility if you have a water cooled manifold, as Richard suggests.

Diesel exhaust gas is about 75% nitrogen, 13% oxygen, 5% CO[sub]2[/sub] and 5% steam. Carbon Monoxide (CO) is a tiny amount, well under 0.5%. The big change over incoming fresh air is the CO[sub]2[/sub], fresh air being about 80% nitrogen 20% oxygen with CO[sub]2[/sub] at 0.04% (and rising, allegedly). A CO alarm will not detect CO[sub]2[/sub].

David

[DBA Forum (B) - Chris Green]

Post by DBA Forum (B) - Andrew Alexander
Harold Thank you but I get masses of air 15 to 20 seconds worth after every
few hours of running . The highest point in the system is my header tank
. We have also checked the calorifier but all appears in order there.

The 'air' must be getting in from somewhere, it can't magically be
created.

So you either have a leak in the system which sucks air in when it
cools down, or you have a gasket leak so that the engine is pushing
its exhaust into the coolant.

[DBA Forum (B) - Nigel Seaman]

Andrew,

Have you checked for air ingress on the suction side of the circulating pump? The suction side of the circulating system will be at a relatively negative pressure, becoming more negative the nearer you get to the pump. This is a common problem with domestic heating systems with people wondering why on earth they have to bleed their radiators so often.
Air will get through a 'gap' that water cannot.
The remedy can sometimes be a tightening tweak on any valve packings that may be present on the suction side of the system.

Regards,

Nige

[DBA Forum (B) - Andrew Alexander]

Thank you for all the advice and I will look at some of the suggestions, in particular the suction side of the pump idea. . The To answer some of the questions posed.
1) I have a dry exhaust.
2) The gas was checked with a chemical kit that attaches to the rad cap and reacts by changing colour.
3) As a result of the problem one of the first things done was to add a secondary expansion tank well above the engine . This had little effect if any
4) I have now checked the skin tank when hot and the gas pressure is already there before it cools down.
5) The system is hot all over when at running temp including the skin tank.

ANDY.A