Hey guys there seems to be mixed ideas about steam coming from the exhaust of inboard engines cooled with raw water. What is causing this and is it a problem? Thanks G

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1985 Gibson 44
Twin 270 Crusaders
Defeated Creek Marina
Cumberland River TN

Are you referring to exhaust gas coming up from the exhaust manifold, through the risers and out the exhaust at the rear of the boat? I'm not trying to be a smart a$$ here but steam coming from the exhauxt usually means one thing and that would be water where it should not be. Do you know if it is actually steam? Can you carefully put your hand in the exhaust and see it is covered in water?

Now that I have gotten this bass ackwards, can you give particulars about the motors in question? Others on this forum who are a lot more knowledgeable about this subject can use that information to give you a better diagnosis.

I hope it does not turn out to be something bad or expensive. Good luck.

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Ken Paulson
1996 44' Gibson Std.
twin 350 crusaders
Upper Mississippi

The answer is: it depends.

How much steam are you talking about and under what conditions?

Raw or closed cooling systems both dump the cooling water into the exhaust so that it flows overboard. The cooling water was warm to start with (having just removed that heat from the engine) and when it gets mixed with the super hot exhaust the water heats up even more. Some of the water could flash to steam.

When this hot water flows out the exhaust it will sit on the surface of the lake/ocean (warm water is lighter than cold water) where the air will blow across it.

I am sure you have seen steam/fog rising off the water on a cold morning. This is because the water is warm enough and the air cold enough to create the fog. When you dump really warm water into the lake it will tend to do the same thing.

On a really cold day it would not be unusual to create a mini fog bank at the back of your boat from this.


If the amount of "steam" that you are seeing is an unusual amount that would not be explained by the air temperature then there is a good possibility that you are not getting enough water flow from your raw water pump. The engines need to have a certain amount of heat removed in order for them to operate properly. This heat can be removed by heating up a large amount of cooling water a little bit or by heating a little bit of water up a large amount.

Keep in mind that the cooling water has to first cool the engine, which will want to be operating at a fixed temperature, usually 160 to 180 degrees. If the water flow is low then the cooling water could warm up to nearly the temperature of the engine core. Next this "warm" water is used to cool the exhaust manifolds (this is different than an automobile). The exhaust manifolds can warm the water up a lot more. Again, if the water flow is low it can raise it to almost boiling. Now the water is dumped into the exhaust where it mixes with really hot exhaust gases. If the water was near boiling to start with it could flash to steam.

If you are not sure if the steam is because the air is cold or because the water is really hot try sticking your hand into the flow of water out of the exhaust. If it is scalding hot you should worry about it. If the water is more like a hot tub then it is fine.


If in doubt, change the impeller on your water pump.


Rod

2 main reasons. 1: Low water level(sea pump issue) as mentioned by abdiver. but be careful the pump could be good and suffering from a restriction ( clogged strainer or old hoses collapsing)  2: internally cracked exhaust manifolds( as they have chambers) I cant fully explain that but its true and I've seen it happen. don't know why they crack. maybe the excessive heat from bad or restricted sea pump....

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Boatless at the moment
www.spboatsales.com

Could just be the weather; it IS winter.

If it happens all the time though, you may have other problems.

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Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

Also check the thermostats to see what the temp rating on them are. On a open loop/raw water cooled engine it should be 160°. A lot of people use automotive t-stats and they are set at 180° and higher.

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UC FANS
1999, 52' Monticello - Miller Tyme
Port of Aurora IN

Well I'll start by thanking ya'll for the advise on this issue. This is an 85 Gibson with twin 270 Crusaders, raw water cooling, strainers with see thru canisters, (dont know the brand) I have started replacing the cooling water hoses, that look original. The water flow is comparible to the other boats in the marina, but its a very real possibliity that the impellers need replacing. It is an old boat and has had several owners and until I go thru everything, I wont know its condition.
Now this steaming doesnt occur all the time, but it happens in warm weather as well as cooler, which led me to believe that there is a problem. The temperature on the gauges appears normal so hopefully replacement of the impellers will do the trick. Something else if the belts are somewhat loose can cause the pump not to function at its peak but I've tightened them and that didnt help. I notice other boats steaming occasionaly and since this is my first inboard, I just didnt know if this is the nature of the beast or a potential problem. Thanks again. Glen

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1985 Gibson 44
Twin 270 Crusaders
Defeated Creek Marina
Cumberland River TN

Have a buddy with an 84 - 44' gibson with twin 5.7's and it "steams" year around, he has gone over everything and it still does it, maybe it is something in the design of this model. I have also seen this on some Hoilday Mansion's with inboards, but not on ones with I/O's.

Good Luck

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UC FANS
1999, 52' Monticello - Miller Tyme
Port of Aurora IN

I have an '84 Gibson with twin 270's. Without seeing the problem it would be hard to say definatively what is happening. However, I just cranked mine up in Tennessee last weekend when it was below freezing and had no steam. But if I ran it hard it would produce some. One thing you might consider. Several people have referred to thermostats and their opening temperatures of 160 and 180. Crusader says that this engine requires a 147 degree thermostat. It makes the engines run cooler than I would think they should be but I got them from Crusader and I don't have constant steam.

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The Judge Rules