R-25 steam from exhaust

[Beerthirty]

Last trip out I noticed steam (not exhaust) from exhaust port after several days operation. Oil pressure and temperatures remained in normal range and coolant level remained steady and normal. Anyone have any ideas? checked for water in the fuel/water separator and didn't note any nor were there any electronic warnings of such.

 

[Capt’nKarl]

It’s probably a lower amount of water passing through the heat exchanger causing a slightly higher temperature. How many hours on the engine? Have you ever flushed the raw water system?

 

[captstu]

look into the sea chest - the filter on the raw line - there should be a very strong flow into the engine. If it had dropped to a trickle, you are missing several impeller blades - if your impeller is over 1 year old, you are lucky it hasn't happened before,.

 

[Beerthirty]

Total hours about 680. Raw water is flushed in the fall and replaced with anti freeze and that is then flushed out in the spring. The screen is checked for debris at each start and there is rarely anything in it. Could it be that my impeller is beginning to wear and as such is not pushing as much water through?

 

[Beerthirty]

Thanks to both Stu and Karl for your replies. I think you have both hit on the impeller as the problem. The boat is a 2010 and I have never changed the impeller so you are both probably right. Thanks very much for your help.

 

[captstu]

Your 2010 impeller should have been changes at least 3 years ago. You are lucky nothing serious has happened. My bot was new-to-me just a month or so when my entire exhaust system melted due to an impeller failure. While you are changing the impeller, install a raw water overheat and/or raw water flow warning sensor. The indicators on my R-25 are dummies - they did not detect the failure because there was no they.

Changing an impeller is unbelievably hard - at least for my stiff arms - but you have to do it.

 

[Brian B]

Beerthirty, I see you have the 25SC, same boat I have. It is a lot easier changing the impeller on the SC than the Classic model.
You gain access to it through the cabin step, laying on your belly. I modified the step for better access, pics in my album. I change my impeller yearly regardless of hours, I can do the entire job in about an hour or so.
Here is a detailed procedure Knotflying wrote a few years ago on performing the impeller change. viewtopic.php?f=5&t=3318&p=26875&hilit=impeller#p26875

 

[dclagett]

I agree the impeller needs to be changed, however if the engine coolant temperature remains in the normal range at cruise speed then your current impeller is working. How much stem is coming out? Depending on the water temperature you are in the exhaust system will produce some steam. On the Chesapeake every spring and fall when the water is colder I have gotten steam from the exhaust in every inboard boat I have had.

 

[CAPTCRUNCH]

I suspect that the main variable leading to visible "steam" from the exhaust might be the dew point of the air at the sea surface. Just like seeing your breath on a cold day, which is probably not "steam" unless you're boiling inside.

 

[dclagett]

CAPTCRUNCH I agree with your technical definition of steam. However, the word steam is used sometimes more loosely such as a steaming hot cup of coffee, etc.

 

[NorthernFocus]

I suspect that the main variable leading to visible "steam" from the exhaust might be the dew point of the air at the sea surface...

Under normal operation water is being injected into exhaust gas which is at several hundred degrees F. There is always water vapor(aka steam) coming out the exhaust. Whether it is visible or not depends on ambient air conditions, specifically dew point/relative humidity as pointed out by CAPTCRUNCH. If the engine is not running higher than normal operating temperature then it is likely just a change in atmospheric conditions that caused what you observed.

That said if you don't know the age of the impeller in the raw water pump it would be a good idea to change it per advice already given by others.

 

[Beerthirty]

Many thanks to you all for your thoughtful comments. You all had a piece of the puzzle, not the least of which was to change out my 8 year old impeller. Other than the steam, everything was normal so the impeller probably is still functioning. Weather conditions and water temps were also factors contributing to the steam and were noted at the time but out of an abundance of caution I decided to ask the group. Glad I did and also many thanks for the detailed replacement instructions.