This thread so future people how to service the Vetus Vented Loop in the engine bay.
This non return or anti siphon valve is used so when you stop your enginewater doesn’t flow into your donks gizzards. (Someone gimme a hand at a proper description, puleeze)
Symptom: Mysterious water leak into the engine room floor of a few liters of water.
Other things probably checked before this: Hose clamps on the raw water system, Stern Gland shaft seal leak; sea cock leak. etc
Problem: The small Valve inside the Vetus Vented Loop has slimy deposit that makes the valve stick in the wrong position when the engine is shut off. The water then siphons and fills the engine room through the escape hose.
Remove the whole thing off the 2 tubes by undoing the hose clamps - no water gushes out.
Remove 2 small screws at the top of the grey Vetus Loop and remove the top thing with the small hose still attached. ENSUE small spring thing stays in place!
Jiggle small spring and its 3 small legs and see if it moves freely.
Pop the black O ring off by jiggeling the 3 black legs
Toothbrush and detergent to clean crap from inside the 3 black legs.
Whack back together and shove on donk, start 'er up and watch for a gusher
Perhaps someone could help with my explanation - I'm not good at this stuff. And correct any errors and add anything I have missed?
Vetus is a much higher quality than the over versions of vented loops that use tiny rubber "joker valves" (like in your MSD). These versions dry out and stick open after awhile. And of course they do not sell the replacement part, so you have to buy a whole new unit.
I serviced mine recently, took it apart just like Mark above, sprayed some "ArmorAll Original Protectant" inside and outside.
Saw the price at my local chandlery, these little plastic gizmos are bloody expensive!