air lock

[johnmoug]

how to bleed and airlock in a Perkins 4-154, thanks

[Ded reckoner]

Crack the sea chest lid (i.e. the raw water strainer for the engine) to allow it displace the air and fill up with water (there likely will be a small amount of air in the top which is okay). Then, unscrew (either most of the way or all of the way) the engine pencil zinc on the raw water heat exchanger. If the pencil zinc is unscrewed most of the way, you will see bubbles as the water fills the heat exchanger and, when it is finished, you will see liquid water coming out the threads.

[SailingHarmonie]

If it is necessary to go through all that to run the engine something is wrong with the arrangement of the plumbing, or with the raw water pump. An engine's raw water system should be 100% self priming.

[Ded reckoner]

If I understood johnmoug's concern correctly, he is referring to an air lock induced when sailing with the engine off. There are many threads in many forums on this subject. To re-establish raw water flow, the system must be re-primed. Please respond again if you have suggestions how to prevent the problem. My experience is an air lock can develop even if the raw water pump is replaced, impeller is replaced, all hoses and hose clamps replaced, lid gasket to sea chest (aka raw water strainer) replaced, raw water exchanger replaced, exhaust elbow replaced, pin holes repaired in sea chest, pin holes repaired in water muffler. My understanding is the air lock forms when the sea chest drains as a consequence of Bernoulli's principle. The question is how to work around this.