steam from exhaust relief

[GlasV162]

Hi all,
The las 2 times I've run our 99 150 efii there has been steam coming from the exhaust relief at idle. I checked all the plugs and they look good, no steam coming from cylinders. The last 2 times running it has been near 100% humidity, so I'm wondering if that's the cause of the steam. It starts and runs great, just getting steam at idle. Any advice? Thanks
John

 

[Charlie61]

Re: steam from exhaust relief

maybe the water pump not getting most water to motor have you rebuild it within the last year?

 

[GlasV162]

Re: steam from exhaust relief

New water pump last summer. Ran it again today and no steam. Good strong stream from telltale. Much lower humidity today.

 

[GlasV162]

Re: steam from exhaust relief

Hi,
Ran the boat again last night--again, the air was very sticky / humid, and we got steam from the exhaust relief. So on humid days we get steam, on dry days, no steam. Is this normal?

 

[Texasmark]

Re: steam from exhaust relief

Have no idea as to being normal. You pretty much nailed it that the engine seems to be running OK and the humidity had an impact on it. Course is it steam or just water vapor. Steam has one connotation, water vapor another. As a final check you might put your hand on your engine block near the top rear and see what it feels like after the engine has been running for half an hour or so. Stat opens at 143F on most Mercs and 140F is the temperature of a domestic water heater water with the thermostat set to normal (mid range).

Mark

 

[Charlie61]

Re: steam from exhaust relief

rebuild water Pump

 

[GlasV162]

Re: steam from exhaust relief

Course is it steam or just water vapor. Steam has one connotation, water vapor another.


Motor continues to run very well with very strong stream of water from telltale. On dry, warm days it shows no steam from the exhaust relief, but as the air gets more humid and / or the air temp drops, that's when we see steam / water vapor. What does water vapor mean as opposed to steam? I pulled all 6 plugs and they all look the same--gas / oil mix on each one, which I assume is good?? I've heard that a shiny clean spark plug is a sign of water intrusion / steam formation--is this correct?
Thanks,
John

 

[Texasmark]

Re: steam from exhaust relief

Course is it steam or just water vapor. Steam has one connotation, water vapor another.


Motor continues to run very well with very strong stream of water from telltale. On dry, warm days it shows no steam from the exhaust relief, but as the air gets more humid and / or the air temp drops, that's when we see steam / water vapor. What does water vapor mean as opposed to steam? I pulled all 6 plugs and they all look the same--gas / oil mix on each one, which I assume is good?? I've heard that a shiny clean spark plug is a sign of water intrusion / steam formation--is this correct?
Thanks,
John

Steam means you have exceeded 212F at one atmosphere (sea level). Your over temp switch is supposed to close at 195F giving you a fault horn warning. Water vapor is just part of the exhaust which contains cooling water from the exhaust manifold water jacket mixing with the exhaust. One is a problem the other is normal.

Yes on the water intrusion into a cylinder. It will be nice and clean. Oil/fuel residue on the plugs when you pull them is normal.

Man you are good to go as far as I can see.

Mark