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Takes too long before the comes out of the exhaust

GJ64

New member
New to the forum. Have a sailing boat with a Volvo Penta engine.

Since this year I hae a rather nasty cool water problem. After sailing it takes about 6 minutes before the comes out of the exhaust. If I have been motoring and start the engine next day, than there is no problem at all. The motor is a MD2020d, Volvo Penta.


What have I done so far?
- replaced the impeller.
- checked the holes in the saildrive where the water gets in
- replaced the o-ring of the water filter (strainer) cover between the inlet and water pump
- made the cover of the water pump house flat again
- replaced the paper between the cover and the water pump house
- cleaned the siphon between the pump and the heat exchanger



Anyone who has a suggestion or solution, that would be highly appreciated.
 

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You might be allowing air into line between the through-hull intake and the suction side of the pump. May be a loose hose clamp.

That hose connected to the pump doesn't look right to me. It looks like flexible PVC. The problem is it's beneath the waterline and very susceptable to cuts or melting. Also (and this may be your problem) it doesn't have the strength it needs to prevent crushing due to suction. I would switch to a good wire-reinforced hose meant for marine cooling systems. Just my $0.02.

Dan
 
Thanks Dan.

I did check all hose clamps and tightened them when needed.

The hose you are referring to is the one put on by the factory, approximately 2002. As far as I can see the hose is wire-reinforced. Given the age of the hose it might be a good suggestion to change it anyway.
 
Is there a heat exchanger or is the engine raw water cooled? Could it be a restriction on the pressure side of the pump like a partially blocked heat exchanger etc? It really does sound like an air leak on the pickup somewhere, but you have checked all that already.
 
Does the cooling water get injected into the exhaust somewhere or is there a separate pipe that it exits the hull in? I don't know that engine, but normally the water from the heat exchanger would get injected into the exhaust system after the exhaust manifod and the part where it is injected will point down away from the manifold do that the water can't flow back into the engine. On a turbo engine the exhaust elbow is usually bolted to the turbo exhaust manifold but without a turbo it will probably bolt to the engine exhaust manifold I expect. This is a really common problem for marine engines as this area corrodes and blocks the injector holes very easily.
 
If the plumbing has not been modified since it functioned properly and there is no sea life obstruction, well, is there a flow thermostat? A partially operational thermostat could cause erratic operation . . . perhaps?
pv
 
If it was the thermostat, why after motoring a day and starting the engine next without any problem, however after several hours sailing it takes a while before the water comes out of the exhaust? I must say, I've never taken out the thermostat to check.
 
The water is injected from the heat exchanger into the silencer onto the exhaust. The Volvo Penta MD2020d is not a turbo engine :) but a regular three cylinder diesel engine.
To see some of the engine http://www.marinepartseurope.com/nl/volvo-penta-cat-7740690.aspx
I googled up an image of your engine. If it is the same image as your engine then there is an exhaust elbow on the end of the exhaust manifold and the outlet of the heat exchanger is plumbed into it. Inside that elbow there are most likely a lot of small spray holes that the water passes through to mix with the exhaust gasses. Have you checked that these holes are clear? This is a relatively high maintenance area for most marine engines and should be regularly checked.
 
If it was the thermostat, why after motoring a day and starting the engine next without any problem, however after several hours sailing it takes a while before the water comes out of the exhaust? I must say, I've never taken out the thermostat to check.
There isn't normally a thermostat on the raw water side of an engine with a heat exchanger. They are on the coolant side and don't affect raw water flow unless this engine is different for some reason.
 
I googled up an image of your engine. If it is the same image as your engine then there is an exhaust elbow on the end of the exhaust manifold and the outlet of the heat exchanger is plumbed into it. Inside that elbow there are most likely a lot of small spray holes that the water passes through to mix with the exhaust gasses. Have you checked that these holes are clear? This is a relatively high maintenance area for most marine engines and should be regularly checked.
I did check the holes of the exchanger. Those are clear/clean. The elbow is on my to do list for this winter, however I have my doubts if that is causing the problem.
 
There isn't normally a thermostat on the raw water side of an engine with a heat exchanger. They are on the coolant side and don't affect raw water flow unless this engine is different for some reason.
I agree with you. I don't think the engine is different ;)
 
I just clicked on the picture of your impeller. Is there any tension on the vanes at all where they are 'straight'? It looks in the photo as if the impeller is slightly too small, but the check is to see how much pressure the vanes are pushing against the pump wall with. If they aren't really tensioned against the wall they will struggle to pump the air through until they eventually get water into the pump.
 
I just clicked on the picture of your impeller. Is there any tension on the vanes at all where they are 'straight'? It looks in the photo as if the impeller is slightly too small, but the check is to see how much pressure the vanes are pushing against the pump wall with. If they aren't really tensioned against the wall they will struggle to pump the air through until they eventually get water into the pump.
Good point. I did ask myself the same question, however the part number of the impeller relates to this engine and this pump. What I can do is try to measure it with a feeler gauge.
 
One possible test of the impeller might be to remove the impeller, then Vaseline (or impeller grease is better) the pump body walls and reinstall the impeller. If it is a bit marginal the Vaseline might help it in the initial pickup. I normally expect the vanes on the impeller to be slightly curved by contact with the wall but those look dead straight in the pic. Could the pump body be worn? Is there also a wear plate at the back of the impeller, and what shape is it in?
If you rev the motor up, does it start pumping more quickly?
 
When I put the impeller into the pump house, I used water resistant grease to get the impeller set.

I'm not sure if the pump body is worn. I asked VP for the correct diameter so I can compare it with the one I have.

I'd expect the rotation of the impeller is always the same way, regardless if the engine is in forward or reverse. However, I didn't test it.
 
Rotation is always the same way. How tight does the impeller feel when installed, and is it a genuine VP one?
 
The impeller is a genuine one €€€€€ Difficult to explain how tight it felt when installing, but reasonable tight.

if the house is worn, would it be possible to lay a bronze cylinder from, let's 0,5 mm in the house, of course with the holes in the correct place?
 
Maybe possible, but would be some very difficult machining. Try googling "Volvo Water Pump Impeller" and click for the images. There are a few there taken from the same angle as your photo and to me all the impeller 'legs' seem to be under more tension than the ones in your photo appear to be.
 
I did see the pictures having more tension on the 'legs' than in my situation. I have tried to figure out the exact inner diameter, however I did not manage to find it nor a Volvo Penta dealer was able (willing?) to give me the diameter. The diameter of the impeller is 50.8mm if I'm correct.

To for come the impeller running dry, I put a one way value in the hose between the strainer and the water pump. After a test sail I noticed the water stayed in the strainer up to the cover of the strainer. Which I think is good. The problem has therefor not been solved, however it is a nice workaround till I have a better understanding of what is going on.
 
Are you saying that with the one way valve the pump starts working straight away now? If so, that could suggest that there may be an issue in the pump. How is the inner wear plate looking? I forget whether you have checked this or not?
 
Are you saying that with the one way valve the pump starts working straight away now? If so, that could suggest that there may be an issue in the pump. How is the inner wear plate looking? I forget whether you have checked this or not?
That's indeed what I'm saying. The pump is getting more and more suspicious. I have not opened the pump yet to inspect the wear plate and the diameter. If you look at one of the previous photo's, you see some curves on the plate. Unfortunately the plate can not be replaced :(

I'm also curious to know the inner diameter of the pump, so far I didn't find anything else than a global drawing of the pump.
 
I used to own a aq225 that had the same issue. I bought a new impeller and it solved the flow problem. The point is check the spec if the impeller first. I also replaced the pump cover with a home made stainless and never had another issue with flow. Another issue was with the manifold gasket to crossover, had closed up due to deposits, but your design might not have a similar chock point. I was getting water in the cylinders and this cost me a new engine, so you are right to figure this problem out.
 
I had the impeller replaced with an original VP one. No luck. I flattened the cover. No luck.

You made a cover from stanley steel and fitted it on a bronze house.. Doesn't that give you any corrosion?
 
Bronze on Stainless with brass screws. If any dialectric problems it would show up in the brass. I was fresh water which helps. FYI look at sailboat hardware... lots of stainless with aluminum, bronze and brass, zinc plate, and iron of course. Its all about trade-offs. Did you straighten the cover? If it has any groves from wear or heat it must be flipped or replaced. It must be flat and smooth. Not a place to cheap out IMO.
 
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