Loud air escape through water discharge hole

[gofishAU]

I recently lake tested a motor I purchased. After I shut the motor off there is a prolonged air escape coming from where the water stream exits the motor. The air escaping appears to be highly pressurized because I can hear it spitting and spraying for several seconds after I shut off the motor. Not sure if this is normal for this particular motor.

Additionally, I discovered that at after running the boat for a short while at mid-throttle a sensor alarm in the control box begins to sound, and when I look back at the motor it appears there is no water stream. After letting the motor sit for a few minutes, I can start the motor without the alarm sounding from the control box and the water is streaming normally. Not sure if that's the reason for the alarm, but it seems to be part of the cause.

I haven't replaced the water pump, so that is the first thing I intend do. Could it be that there is a bad seal and exhaust gasses are leaking into the water pump?

Motor:
1994 Merc 150 XRI (2.5 ltr)

-gofishAU

 

[jbh3]

The engine appears to be overheating. Start by replacing the water pump and all associated gaskets. There is a Mercury "kit" with all the components. Do not continue to try to run the engine until this issue is resolved. Good luck!

 

[gofishAU]

Thanks for the reply and info!

 

[wrechin2]

Hissing is probably a leak in the pressurized oil tank system on the engine. Is the alarm a solid tone or a beep.beep.beep? A mercury does not always pee because the thermostats control it. That is why a water pressure gauge is a very valuable thing. ALWAYS a goog ideal to replace the water pump on a new purchase.

 

[gofishAU]

James--the alarm was a solid tone. Sorry, I did not see your reply. Are there any typical trouble areas where the system will develop a pressure leak?

Update: There were 3 or 4 large chunks of rubber stuck inside the fuel pump housing. The old impeller was still intact, so I'm not sure where they came from. I ended up replacing the entire assembly just to be safe. I'll get to lake test near the end of the week.

However, I do have a new question. I figured I'd go ahead and rebuild the fuel pump. The kits come with what appears to be 4 check valves: 2 rubber, 2 clear plastic. One place online I read that the plastic ones are intended to replace the rubber ones for motors that run on blended ethanol fuel. Other areas I researched lead me to believe the plastic ones are intended to be used as the retainers for the rubber check valves. Any idea what they are actually for?

 

[jbh3]

If you found rubbery trash in your fuel pump you probably should look into changing your old fuel line and bulb to the newer ethanol resistant parts. I'd do that in conjunction with the fuel pump rebuild. James will have to help you with the valve question.

 

[wrechin2]

Solid alarm is overheat. Those pieces may be from a previous failure and had been trapped in the lower. I assume you meant to say the chunks were in the water pump housing. If not the fuel hose is coming apart. On the valve I use the plastic ones only and sometimes have to install check valves in the fuel line to prevent the fuel from draing back as the plastic does not seal as well as the rubber. Just under the starter is the pulse limiting valve that is a common place for a hissing type noise but it could be anywhere in the pressurized system. The oil system is not the best and any mercury I build thT is the first thing removed as they are too many issues that could cost you a engine. Hope this helps.