Water come from header tank pipe

[Dave Bebb]

I all a few week ago i saw a comment on here about header tank on his Isuzu 35 hp engine losing water i had the same problem ,so i thought i would start from the easiest first so bought a new filler cap for the header tank just in case the spring was getting weak,well it came today gave the spring a press and its was a lot stronger looked at the old on and the new one was twice as much pressure rated than the old stamped on the top PS its a genuine Isuzu one i just bought for a 25/35/42/55/70 HP engine think that was the problem so if anybody has the same problem just check you have the right header cap fitted first before pulling things apart . hope this might help some one else .  

[Tony Brooks]

The pressure rating of the cap should have no effect on the water coming out of the overflow UNLESS the pressure is so low and you are driving the boat so hard the engine is suffering localised boiling. This will not show on the temperature gauge. It may also have an effect if the skin tank is undersized (as many are) and it has raised the boiling point of the coolant sufficiently but then the gauge should show overheating.

The usual cause is people overfilling the header tank (ignore any level marks on it - they will NOT be for tank cooled boats) so it overspills when the coolant expands.

I feel you haver hidden a problem rather than cured it.

 

Edited July 5, 2017 by Tony Brooks

[Dave Bebb]

Only got a light for over heating and a buzzer and its never go off i think it had the wrong header filler cap fitter  had the boat for 4 years a done about 300 hours in her .i will put the new header cap on and see if it fixes the problem might get one of the heat detector things just see if there is any hot spots  

[Tony Brooks]

Look at it this way. The cooling system has a finite capacity. The coolant temperature rises through a finite number of degrees. That means the expansion of the coolant will also be a finite amount. If you know the capacity of the system and the temperature you can work out the  amount of expansion. Once that expansion has taken place it is impossible for the coolant to expand any more unless the temperature rises. The job of the header/expansion tank is to accommodate this expansion but because they are often made for trucks etc with a far smaller coolant capacity any level markings are likely to be too high.

Refill when the engine is off but at at running temperature to the base of the filler neck. When the engine is cold mark the coolant level on the tank. This is the correct topping up level for your boat.

There is a problem when you do not bleed all the air out of the system an din that case air expands far more than water when heated so even if you do not overfill the   system it still overflows when heated.

The pressurisation has NOTHING to do with keeping the coolant in the engine. It is to raise the boiling point of the coolant so it can not boil on internal hotspots when under high loads.

[fv1801]

I too have an excess of coolant coming from the header tank on my 2002 35hp Isuzu engine since purchasing the narrowboat nearly 3 years ago, mainly when working harder on rivers and have also traced it to the coolant cap. I have found that when the cap is turned into place the seal and spring assemby is not long enough to form a seal on the neck shoulder hence the coolant has free unhindered access to the overflow tube. Its my understansing that If the seal contacted the sealing lip of the filler neck it would pressurise the system keeping the boiling point higher and preventing free unhindered expansion of coolant. I am going to order the proper filler cap from quayworks. Its notable that the existing filler cap currently on the header tank looks like its been in the boat since new so maybe a more common issue than realised.

[Dave Bebb]

16 minutes ago, fv1801 said:

I too have an excess of coolant coming from the header tank on my 2002 35hp Isuzu engine since purchasing the narrowboat nearly 3 years ago, mainly when working harder on rivers and have also traced it to the coolant cap. I have found that when the cap is turned into place the seal and spring assemby is not long enough to form a seal on the neck shoulder hence the coolant has free unhindered access to the overflow tube. Its my understansing that If the seal contacted the sealing lip of the filler neck it would pressurise the system keeping the boiling point higher and preventing free unhindered expansion of coolant. I am going to order the proper filler cap from quayworks. Its notable that the existing filler cap currently on the header tank looks like its been in the boat since new so maybe a more common issue than realised.

My new header cap came and its a proper Isuzu one but when i looked at the pressure it was twice the pressure than the old one i took off thats fixed it ,now i have just fitted a water temp gauge to day and that works fine to only left engine running for about 10 mins and it got to  60 when out on the cut it should get to 75 to 80