Volvo MD7A Exhaust flow

Gk 66

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When i lifted back in a last weekend I notice that the water flow from the exhaust on my GK29 was a bit weak. I have checked the
Inlet strainer clear
Pump impellor OK
Removed and manually cleaned the exhaust manifold and leg
Checked that the siphon line is clear back to the cockpit

I now have no water coming out of the exhaust. Is it possible that the exhaust gasket is backpressuring the water rail?
 

Martin_J

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Small question - You mention that the impellor looks okay. Even if it has all the blades - did you check that the rubber part is not turning on the metal collar that fits to the shaft? It is not unknown for the join between the two to slip...

By checking exhaust... Is there an exhaust elbow where the cooling water meets the exhaust gases that you didn't check?

You have presumably checked for free flow through the open seacock haven't you and not just checked that the strainer is not blocked...
 

vyv_cox

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A worn water pump face plate can cause priming problems. Make sure the pump primes by filling the seawater hoses and strainer before starting the engine and if this solves it, either turn the plate over, if this is possible, grind it flat or replace it.
 

capetown

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MD7A

Aslo check the pump face the other side to the cover, mine was so badly scored that I had to fit a new pump.

If you have to do that, the original pump is obsolete. (at least mine was)

Key Part have a replacment but you will have to do a bit of plumbing.
 

Gk 66

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The exhaust has been checked clear as far as the Vetus muffler. I also primed the top of the raw water strainer. The sea cock is working fine, with water flowing right up to the pump inlet. i actually put a new impellor in the pump this pm to eliminate this from my enquiries. I did notice some smoke coming out of the top of the water rail when I ran it with the syphon line disconnected, so I will remove the exhaust manifold tomorrow and stick it back on with some hi temp gasket gunk. If exhaust pressure is getting into the water side of the manifold, it could be causing the system to backpressure.
 

Gk 66

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The raw water pump was mounted upside down. When I had inspected the impellor in the past, I had always replaced the pump in the same way it came out. After carrying out a test of the pump with the discharge pipe disconnected, I noticed that the water in the pump body was vanishing back down the inlet side. After a quick experiment involving a cordless drill and a bucket of water, I put the pump back in the other way round and Robert was my mother's brother. It speaks volumes about the sturdiness of the volvo lump to consider that this state of affairs had been going on for at least 18 months.
 
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