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Old 04-19-2017, 02:06 PM   #1
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Exhaust water output

Hi to all,
I need some opinions about exhaust water output. On my port engine ( volvo tamd 41a) I am getting very little water coming out of the exhaust. I have replaced the impeller, checked the heat exchanger, changed the thermostats, checked the transmission cooler, Looked in the top of but did not pull apart the After-Cooler seamed to look OK but as I said I only looked in the top.
Before I tear into this what are your opinions about this.
Thanks in advance for any help.

Gordo
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Old 04-19-2017, 02:11 PM   #2
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Questions-- Is the engine over heating? At what RPM is your water flow low? Last but not least, how do you measure water flow?

At idle my RW flow is low too. Normal behavior. Flow and RPM are related. Keep us posted.
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Old 04-19-2017, 02:22 PM   #3
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Originally Posted by Gordon B View Post
Hi to all,
I need some opinions about exhaust water output. On my port engine ( volvo tamd 41a) I am getting very little water coming out of the exhaust. I have replaced the impeller, checked the heat exchanger, changed the thermostats, checked the transmission cooler, Looked in the top of but did not pull apart the After-Cooler seamed to look OK but as I said I only looked in the top.
Before I tear into this what are your opinions about this.
Thanks in advance for any help.

Gordo
I assume when you say your port engine has very little water coming out of the exhaust, the starboard engine has a lot more? One place that can definitely cause a restriction over time is the exhaust "elbow" or mixer. It is where (usually) all the raw water exits the cooling circuit and enters the exhaust hose. Exhaust mixers are often made of cast iron and over time heavy rust scale can develop inside and block the flow of water.

Another place that can restrict water flow that you didn't mention checking is the water scoop (or whatever you have) and raw water inlet seacock. That could be blocked with layers of paint or a heavy crust of barnacles or other sea creatures.

I have also heard (here) of raw water hoses failing internally and blocking water flow that way.

Ken
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Old 04-19-2017, 02:24 PM   #4
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low flow can cause the exhaust tubing to overheat and even catch fire.
Is that side louder than the other????
It is good that you are alert to this issue. Check the inlet scoop and strainer. then there is little choice but to open all the sections and identify the problem.
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Old 04-19-2017, 03:18 PM   #5
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On one of my TMD40s, the tube from the seawater pump to the oil cooler was blocked with salt from the engines not bein' used by the PO.
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Old 04-19-2017, 03:26 PM   #6
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Gordon:

Here are some causes of low raw water flow in approximate order of likelihood.

0. Fouled strainer
1. Bad impeller
2. Plugged exhaust mixer
3. Fouled exchangers
4. Bad raw water pump cam
5. Marine life in raw water pickup, seacock, strainer or hose
6. Collapsed hose

0 and 1 are easily checked. You can check for 2 by removing the hose from the mixer and start the engine while the hose is pointed towards the bilge. Compare to other engine if necessary.

You can check for 3 by removing the outlet hose from the pump and running the engine for a few seconds.

The others require disassembly and inspection.

David
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Old 04-19-2017, 03:38 PM   #7
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I have a TMD40 also and the flow at idle is very low but no overheating problems and lots of flow at cruise speed. I did have a blockage last year at the thru hull fitting and was able to clear it without diving by taking the hose off the strainer and putting the deck wash hose in it and backflushing it. Lots of good suggestions already for you, and not likely anything serious but it certainly needs to be checked out for your peace of mind if nothing else. Good luck and let us know what you find.
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Old 04-20-2017, 01:04 AM   #8
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An often overlooked reason for low water flow can be pieces of a previously destroyed impeller lurking on the INTAKE side of the raw water pump.
Collapsing or delaminating intake hoses can also do it.
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Old 04-20-2017, 06:00 AM   #9
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Some boats with high cooling requirements pump more water than the boats exhaust system can eat.

A by pass that only allows enough water into the exhaust to have it operate is installed.

Perhaps look for this and open the valve a bit more?
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Old 04-20-2017, 08:14 AM   #10
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WOW! Thank you all so much for the responses.
When I brought the boat down to FL. from NC. I did get a bit of an over heat at around 1800-2000 rpm.
The boat just came off the hard and the scoops are clear. Everything seems to be OK but I have not checked the exhaust elbow mixer or if the hose is collapsing. I will keep at it and check all the things mentioned in the responses.
When I figure this out I will post the fix.
Thanks again
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Old 04-20-2017, 01:22 PM   #11
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If you do 't know the maintenance history on the boat, or if you know the exhaust elbow, injection ring, coolers and hoses have not been inspected in a number of years, it's probably worth the time to take those things apart for a good cleaning and inspection. Doing the work at your convenience dockside beats the heck out of breaking down somewhere.
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Old 04-20-2017, 03:27 PM   #12
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Gordo,

I also have a TAMD41a. Assuming your starboard engine is pumping more water than the port at the same RPM & temp and you dont see anything leaking, I would follow DMarchand list with one addition. I would look for broken off pieces of old impeller in the oil cooler which is located on stbd side of engine under the heat exchanger. If you have the original oil cooler I would also consider having it serviced (or replaced). When I replaced my old oil cooler I took it apart and found there was a lot of impeller chunks blocking the grate and restricting water flow. After almost 30 years its to be expected. If its all original from the raw water pump to the oil cooler its probably connected by a rigid copper pipe that is a bit of a pain to take off. If you can get it off so be careful with it. My other comment would be to replace the exhaust elbow if its more than 5 years old. They are inexpensive enough.
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Old 04-20-2017, 05:15 PM   #13
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Heat exchangers are the 1st place to look. Mixing elbow is 2nd. Make sure the SW intake is clear. Also some people put in higher volume SW pumps (common in warm waters) and have a valve to divert some of the water. If the valve is open too far, not enough water goes into the exhaust. My Detroit mains divert some to keep from overwhelming the muffler.
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Old 04-21-2017, 12:34 PM   #14
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Heat exchangers are the 1st place to look. Mixing elbow is 2nd. Make sure the SW intake is clear. Also some people put in higher volume SW pumps (common in warm waters) and have a valve to divert some of the water. If the valve is open too far, not enough water goes into the exhaust. My Detroit mains divert some to keep from overwhelming the muffler.
My mechanic just used a thermal imaging device and found that the heat exchanger is hot, so I guess I'll start there. I cleaned and flushed it on the trip down but I didn't take it apart.
Hopefully, this will solve the problem.

Thanks
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Old 04-21-2017, 02:24 PM   #15
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Well of course the heat exchanger is hot, this is what the thing is all about!
You need to physically examine the ENTIRE raw water system, from intake grating to exhaust outlet by dismantling and inspecting and cleaning each part and hose.
If you find a few impeller bits or some corrosion in one spot, don't assume that that is the entire problem, the offending bits can be distributed throughout the system.
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Old 04-21-2017, 04:45 PM   #16
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Well of course the heat exchanger is hot, this is what the thing is all about!
You need to physically examine the ENTIRE raw water system, from intake grating to exhaust outlet by dismantling and inspecting and cleaning each part and hose.
If you find a few impeller bits or some corrosion in one spot, don't assume that that is the entire problem, the offending bits can be distributed throughout the system.
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