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.