Log in
Article search:

Q & A

Raw water cooling

I have a raw water cooled engine and while the water spits out of the exhaust I have another water outlet on the stern side which runs constant stream of cold water only when engine is running, following the pipe it goes to a type of plastic valve then pipes run to engine can you explain what is happening and how to stop it or is this natural, sorry to be a pain as we only picked up boat last weekend thanks jim

Asked by: Jim Bratt  | 7.02pm, Friday 16 August

WW says:

The extra pipe is a vent which allows water to flow out from the raw water cooking when it is running, and to allow air to vent back in when the engine is stopped. This prevents water being drawn back up the wet exhaust into the cylinders- which could be expensive. They are a normal fit- and a sign that the engine installer knows how to fit the system properly. The vent pipe would also prevent water being drawn back into the exhaust if the main exhaust outlet is submerged and, as the gases cool in the manifold, water could otherwise be pulled in.
The vent should leak water all the time. It is possible to bit a vacuum vent (for example, Vetus sell both types) which eliminates the dribbling, only allowing air into the system when the engine stops- but they require periodic maintenance and are not so foolproof.
If we can be of any more help, please let me know.

Mark Langley  | 10.53PM, Friday 16 August

You must log in to post an answer.