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Uneven water flow

luhrs_40

luhrs_40

Contributing Member
Crusader 454 closed coolant...Only in idle water flow constant for a few seconds then nothing for 3 or 4 seconds and then big burst of water pressure..When is running over 900RPMs water flow is fine..Replaced elbows and risers a few months ago , impeller is new I took out heat ex changer and oil cooler and had them cleaned but they looked fine and not plugged All hoses are less then 2 years old Am i missing something? The temperatures are around 165-170 degrees but worried about the future since i troll in idle fishing over 200 hours a season.
 
I presume by "water flow" you are referring to observing the water coming out with the exhaust. You could pull the zinc from the heat exchanger and attach a pressure gage to see if you are getting pressure changes in the raw water system that correspond to the observed bursts of water. If it is a failing intake hose it should show up there.

To me, a more likely cause is in the exhaust system itself. Something could have changed to allow water to collect and then come out in a burst. Perhaps a failing muffler or a low spot created when you disconnected and reattached the exhaust while changing the elbows?
 
Hoses are all good..Have disconnected raw water hose going from oil cooler to heat ex changer while engine is running and the flow looks good . What ever it is its from heat ex changer and after..I guess there is no way to check muffler is there? Also the problem was there before i changed the elbows and risers
 
2X what DD said (post #4)....as far as checking, I'd start with opening the hatch(es) and seeing what is under the deck....
 
Both engines doing this?
Do you have exhaust flappers on both, and are they intact?

So, the deal with engines/exhausts below the waterline is that the mufflers are special. They build up exhaust water until the exit is blocked by this water, then the pressure builds, and then, they spurt out water. Many aux. sailboats do this. Unusual in most powerboats, though.

Let's say a flapper is missing, or not sealing on your boat, and the waterline lets in outside water into the muffler. This water that is running in doesn't blow out the system continuously, but takes some buildup in exhaust pressure to relieve. At higher power settings, this happens very rapidly.
 
Gotta agree here; that's how our Crusader 350 (s) have always operated out the exhaust. Post engine rebuild, I checked the water flow out the exhaust manifolds and at that point the flow is steady and even so I was never really concerned about the exterior water surge at idle.
 
luhrs_40 said:
.... You saying taking muffler a part?
Click to expand...

You gotta remember, we aren't at your boat...and you haven't mentioned if there are mufflers in the exhaust lines....figuring out what you have is necessary to determining if there is a problem..
 
Only starboard engine does it Yes there are flapers both sides.. I think the problem is from heat exchanger and before the muffler. I say this because right after the riser on the exhaust hose before the muffler i have installed Borel sensors with alarms, when water flow is low or not there the alarm goes on.. And when i am trolling on that engine around 650 RPMs the alarm goes on...when i bring the RPMs up it stops
Does the raw water go to the exhaust manifolds before it goes to the elbows? If it does can it be plugged before it goes to the elbows?
 
luhrs_40 said:
Does the raw water go to the exhaust manifolds before it goes to the elbows? If it does can it be plugged before it goes to the elbows?
Click to expand...

No, and unlikely. I would take an IR gun and start measuring the temperature of the TOP of the large exhaust hoses, compared to the sides of the hose at idle.
Or, take your hand and feel for hot spots. At idle, you should be able to touch all the hoses comfortably in the exhaust system, even true at cruise.
Are you sure that at cruise, 3200rpm, all is well?
 
At cruise everything is fine..Before i pull her out for storage i run 20 minutes at 3600 rpms and temp was around 170 both engines Well got to wait till spring and take an other look.. Thanx for all the help
 
I was not familiar with Borel sensors so I Googled them and was quite impressed with their products. In seeking to learn more I ran across an excellent article by Steve D'Antonio, a marine consultant (article is farther down the Google page). He highly recommends the Borel products but states: "Counterintuitively, water-cooled exhaust systems will overheat when the vessel is operating at low rather than high speed; at low speed less water is pumped into the exhaust system, often leaving the upper portion of hoses dry." [See Diver Dave's advice above] When you read the entire article you realize there is a gray area. The acceptable temperature limit anywhere on the hose is 200F but 150F or less is desired (and will be achieved in a "well designed exhaust systems"). The Borel sensor is set to go off at 165F. So it could well be that the top of your hoses have always run north of (or right around) 165F at idle (but less than the 200F limit) and you are chasing an alarm problem with your new sensor that really is not a serious issue. A careful look with the IR gun at various rpms is really the only way to know. If your worst case temperature is still significantly below 200F you could consider rotating the sensor to a cooler location (slightly lower on the hose) so that it would indicate a problem if something changed and then live with system as is. Also consider that the sensors could be 5 degrees off and that could be the difference between engines (one alarming, one not). Or whatever. But careful recording of hose temperature is the only way to know. What all this has to do with the splurging water in the exhaust I don't know but if the temps are under control then likely that is something you can wait and see on.
 
Interesting... I will double check with The IR gun in the spring and also will move Borel sensor from top of hose either at the side or in the bottom Thanx again
 
Yeah, I was thinking of the 1 hole vs 3 hole gasket choice too. It may be helpful too to know which elbows and risers are used.
 
I had the problem before i changed elbows and risers..Thats why i had them change I thought that was the problem at first
 
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