Fuel line return

[jimhuggins0350]

I have 1986, PS 34. My question is there are two air vents near where fill hole for diesel tank. First one I am guessing is overflow vent when filling the fuel tank. My question relates to the second vent and its function. My second vent is flowing out clear liquid when the engine is running. Need some advise before I try to fix the problem. It doesn't smell like diesel but it does leave a stain in water. Maybe its unburned diesel but before I route it back to diesel tank need a little input.

[RainDog]

A picture might help. You are talking about air vents in the cockpit near where the fill hole on the bridge deck is? or on the tank?

What is the temperature of the liquid flowing out? If you put some in a cup and then add water, do the two mix, or stay separate?

[jimhuggins0350]

air vent in cockpit, the liquid is not hot or warm, I will do the "add water test" and let you know the findings, thanks for advise.

[RainDog]

Strange. I have seen a boat that plumbed the engine freshwater intake to a cockpit vent so you could see if the cooling system stops pushing water. If it is water, it is possible that is what it is, but I doubt the factory ever did that.

Have you traced the hose of the back of the vent to see where it leads?

[jimhuggins0350]

Good advise I will trace the hose, Thanks

[niftynickers]

The vent that you are referring to is for the vented loop in your raw water line to the injection elbow in your exhaust system.If it is spitting liquid that's an indication that you should service (clean) the vented loop.To find the vented loop follow the hose back from the injection elbow,on the 37 its under the coaming on the starboard side just above the expansion tank.

good luck,
Dianne and Chuck Burke S/V NiftyNickers C37 #139

[DaveMancini]

I have also seen boats where the one way valve at the top of the vented loop was removed to eliminate the possibility of the valve getting stuck closed and creating a syphon. But, this also meant that a little water would continuously flow from the loop into the cockpit when the engine was running (a good sign). One proponent of this lash-up was Hal Roth.

Dave Mancini
s/v Swan, PSC 34 #305