Volvo Penta 2030D SW cooling air locking

[yotter]

I apologise in advance as there have been previous threads on this., but I still l have an intermittent issue
My VP2030D raw water cooling airlocks after a brisk sail, we only fine the issue after starting the engine at sea before mooring or anchoring which is not the best conditions to fault find. This seems to be intermitent and perhaps becoming more frequent. Yesterday, it was air locked after the boat siting in the marina since last weekend when it was fine. I suspect a small air leak somewhere, possible the water pump or the Vetus water filter. The normal mitigation is to shut the inlet seacock, remove the water strainer lid, fill with water, replace lid, start engine then open seacock as soon as possible. I bit of a pain:-(

Impeller recently changed (but I could try this again)
New hoses were recently fitted
Hose clips all tight
New SW pump cover plate
Engine runs at 70 degrees at 2500 rpm which is pretty normal (with cooling!)

I wondered if I could take the water filter out of the circuit to eliminate it as a possible air leak, would this be sensible, I will shut the intake seacock when the engine is stopped.

Any ideas appreciated

 

[Tranona]

Only thing missing on your check list is the seal on the cap. Clean and lubricate with silicone grease before replacing. Is your seacock well under water? - not relevant if saildrive.

 

[yotter]

Tranona,
Many thanks, its a VP 130S saildrive so sea water intake is well underwater. The seal on the seperator looks good and has silicone grease on it. I suspected the water filter hence thinking about by passing it. The other possibility is the pump but difficult to bypass
Angus

 

[jwfrary]

Check the rear pump seal, you may see signs of verdigris if it's leaking

 

[Daydream believer]

If you have bought a non volvo impellor it may be a fraction of a millimeter thinner than a volvo one & that could be the problem. I have had non volvo ones that have caused problems
I note that you have replaced the plate to the front of the pump. I just cleaned the paint off mine & turned it round. Later I bought some brass & made one for less than 1/3 volvo's price.
Also check there is no back pressure caused by partially blocked heat exchanger, exhaust elbow etc.You can do that by squeezing the bellows each end of the exchanger to see if they are under pressure when the engine is running

 

[yotter]

Check the rear pump seal, you may see signs of verdigris if it's leaking

John,
Many thanks for that, I will have a look, but suspect not an issue since bilge is dry (but apprechiate that the water may evaporate leaving just the salt). I will have a closer look.

 

[dje67]

I've had a similar problem in occasions with my MD2040. After a brisk sail, the water pump took several seconds to achieve a prime & flow. I did all the checks you have mentioned to no avail.

However, I did spend a happy 10 minutes looking at the clear cooler inlet pipe to the filter from my raw water strainer. When under sail I could see a continuous stream of air bubbles coming up the pipe. Over time I think this allows the strainer to empty sending air to the pump. I cannot explain how air bubbles could be getting into the intake pipe at a depth of 3/4m below water level (without signs of water weeping into the boat when not sailing. My best-guess is that air bubbles are tracking along the hull and somehow entering the raw water strainer.

 

[yotter]

If you have bought a non volvo impellor it may be a fraction of a millimeter thinner than a volvo one & that could be the problem. I have had non volvo ones that have caused problems
I note that you have replaced the plate to the front of the pump. I just cleaned the paint off mine & turned it round. Later I bought some brass & made one for less than 1/3 volvo's price.

I have been wondering about back pressure in the heat excaahner, so will try your test of beeling the bellows. I am fairly sure that I removed the pump outlet pipe and blew air down it which I managed but this is pretty unscientific. I am also thinking that a genuine VP or Jabsco impeller may make a difference, I cannot recall the make fitted. I have fitted clear pipes so can monitor for bubbles.
Angus