Engine cooling water flow not normal

[Beckytek]

After starting my gas Crusader 454's the other day, I noticed an unusual water flow from the exhaust pipe of the starboard engine. The flow was normal for the first 4 minutes, a nice steady flow. Then there was a large gush of water followed by no to very little to normal flow again. This was repeated every minute or so.
I proceeded to change the raw water impeller on that engine. There was no change in the water flow pattern.
I'm sure there is no problem with the heat exchanger and other components. The engine never has a heating problem, always stays at 160 degrees. I back flushed the system this spring and the impeller I removed was perfect.
Could this be a sign that my risers need changing? It's been about 3 years since last change.
Ron

 

[ian w]

I have the same situation with detroit 871 ian w

 

[MikeP]

Sounds like the muffler is filling with water and then, when the level gets to the point where it is blocking the exhaust, the exhaust blows it out, then it refills again. This is typical of lift-type mufflers and regular in-lines can do it too, depending on how the exhaust hose/tube runs.

Has there been any recent trim change in the boat? If, for example, the in line muffler was normally just on the edge of filling to the blockage point and something was added that changed the angle of the boat in the water, it could be enough to start that happening. Some boats do it/some boats (same model) don't. But obviously if it didn't do it before and now it does, something changed. Whether it's important or not will depend on what it was.

I can't see how a bad riser could cause this problem but general recommendations are that risers in salt water should be changed every 5 years as normal maint to avoid serious engine damage. If you don't know when the risers were last changed, I'd change them now so you have a valid starting point.

 

[ian w]

My detroit 871,s are in a 1981 motor yacht .I will keep an eye open to see if this is only happening when aft fuel add water tanks are low when exhausts under swim platform are almost out of the water.How do you know when stainless risers are worn out.If they wear out can water get back to form aqualock ian w

 

[REBrueckner]

Speed up from idle RPM to, say, 1,000 RPM and check the water flow. Likely the pattern will remain but with a lot shorter interval of "little water".....that's your feedback the water is collecting....no big deal....

My 8V71TI's (1972 48 YF) dockside would burp a solid exhaust full of water and douse the dock...and feet nearby. There was a dip in the exhaust hose..a low spot maybe six to 8 feet in from the stern and while water would flow at all times, it still built up in the low spot before erupting...flow was smooth and normal at cruise RPM with the bow higher than the stern.

 

[UNIQUE_NAME]

After starting my gas Crusader 454's the other day, I noticed an unusual water flow from the exhaust pipe of the starboard engine. The flow was normal for the first 4 minutes, a nice steady flow. Then there was a large gush of water followed by no to very little to normal flow again. This was repeated every minute or so.
I proceeded to change the raw water impeller on that engine. There was no change in the water flow pattern.
I'm sure there is no problem with the heat exchanger and other components. The engine never has a heating problem, always stays at 160 degrees. I back flushed the system this spring and the impeller I removed was perfect.
Could this be a sign that my risers need changing? It's been about 3 years since last change.
Ron

ron,

i have an older model of your boat. this is how my exhaust functions all the time but its because my risers dont have enough height to give the exhaust full downhill run. it is actually
more pronounced when i am low on fuel with the tanks being so far aft. if yours never did it before i would look for something like mike suggested. you might also want to check the exhaust hose and the muffler. the hose may have a developed a bubble inside or a baffle in the muffler may have given way and is causing a blockage. long shots yes, but i had the hose do just that to me on a previous boat. good luck

jim

 

[eze2bme]

Check the straps holding the exhaust system/muffler in place ... maybe one of the straps has come loos and allowed the forward part of the exhaust to become too low thus causing the water to accumulate ... just a thought.

 

[Beckytek]

It just dawned on me that I am very low on fuel and the water tank is empty. The bow is probably a little lower in the water. I noticed this when taking a shower and the water accumulates toward the bow now. That is about the only thing that is different. Thanks for your advice, I never would have thought of that. You guys came through again. Ron

 

[Beckytek]

I went to the boat today and filled the water tank. Started the engines and nice even flow of exhaust water. Another mystery solved. Thanks guys. Ron