VP 2020 cooling problem

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brians

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I have a VP 2020 with saildrive. At tickover and speeds up to 1750 rpm the seawater cooling works fine and gushes out the exhaust. Once I get to 2000 rpm and above the water throughflow virtually stops, white smoke or steam appears from the exhaust and it sounds like a tractor.

The impellor is new and is clearly working as is apparent at low engine speed. The seawater filter is clear so perhaps there is a partial blockage in the seawater intake in the saildrive leg.

Has anyone had silmilar problems or any idea what it may be?
 
Bit of a long shot but could any of the hoses be collapsing internally .

cant think of anything else.
 
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Is it the infamous rubber impellor debonding from the bush

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He said new impeller. It would explain the symptoms but doesn't the impeller driving screw go though the rubber as well. It is not one driven via a key bearing on the centre bush only.

Its definitely something that should be on the list to recheck!
 
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I would check the engine thermostat

[/ QUOTE ] The thermostat only controls the flow of coolant through the engine. It will have no bearing on the total seawater flow.
 
FWIW just removed the exhaust riser / elbow from my 2030 to find it clogged virtually solid with corrosion products. the sea water came from the exhaust as if the boat had prostate problems.

what you describe is restricted flow and there are a limited number of places this can happen: blocked inlet, collapsing hose between inlet and pump, impellor, blockage between impellor and where the cooling water is injected into the exhaust pipe.
 
Have just had same problem with our VP2020. These are the key things to check for seawater system.
1. Check that all hose connections are tight. Easy and essential check!
2. If you have dried out, check that there are no airlocks in the system and keep filling seawater filter until there is no air in it. (need to close seacock each time you undo filter top)
3. If you think the water intake may be blocked remove hose and blow down it with fog horn to clear any debris.
4. Is the water pump leaking at all? If the shaft seals or front gasket are leaking then it will suck in air. If you have any signs of oil or water seepage at back of pump then it probably needs overhauling/replacing.
5. Is the inside face of the water pump badly worn? If so it needs replacing. (I have just fitted a SpeedSeal in mine)
6. Have any impeller blades broken off in the past? If so they may be sitting at the intake of the heat exchanger.
7. Could the heat exchanger need descaling/cleaning?
If you are getting steam coming out of the exhaust outlet then there is not enough water flowing through and would soon burn out the impeller. Hope this helps.
 
Thanks for this, I will try all.

With regard to your item 3 I guess you did this out of the water. Mine is still afloat and trying to avoid a lift out.

Did you have exact same problem as me i.e absolutely normal up to about 1800rpm but any higher water throughput stopped completely? |It is this I am having trouble getting my head around.
 
Sounds like a blocked heat exchanger - easy to check, just remove the rubber boot from each end and slide it out. You will have to drain down the freshwater first, unless you want to lose half of it.
It's worth giving the exchanger tube a good soak in descaler as the freshwater channels can fur up as well leading to over heating problems, esp. if the antifreeze is not changed regularly.
I would check the exhaust elbow as well, they need replacing from time to time as they corrode heavily.
 
If you are in a marina, the best way to clear an inlet blockage is to connect a mains water hose to the inlet at the sail drive or just above it and turn on. However, you can tell if there is a blockage because if you take the inlet pipe off the water filter and push it below the water line, there should be a good jet of water, anything less and it is blocked. Finally, if your hoses are transparent, you can see straight away that air is being sucked through the pump bearings/seals by the water into the heat exchanger being full of air. It is much easier to check the inlet than clean the heat exchanger!
 
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With regard to your item 3 I guess you did this out of the water. Mine is still afloat and trying to avoid a lift out.



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If the open end of the pipe is above the waterline, before opening the seacock, then this can be done whilst afloat.
 
Tony
I'd be very careful about doing that because if the exhaust has a swan neck in it you could fill the engine with water if it's not running????

Peter.
 
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