Cooling system problem Volvo MD2030B

[Int14]

16 year old MD2030B with indirect cooling.
About 2 litres of fresh water coolant pushed out of pressure relief pipe under header tank cap. When all cooled down, found header tank/heat exchanger still full with coolant. Ran engine again for 3 hours, no further coolant forced out, however, after over a week since running engine, when opened cap, coolant spurted out 1-2 feet, so still pressurised.

Have isolated hot water cylinder circuit with two valves, so not relevant.
As header tank/heat exchanger stays full of coolant to brim, assume must have leak between fresh and sea water cooling circuits, but why is system staying pressurised for days afterwards? Also, have read elsewhere on this forum that sea water circuit is under less pressure than fresh water side, so how does it get in?
Replaced exhaust manifold a few years back due to blockage, so this should now be fine. Plenty of sea water coolant comes out of exhaust when engine is running.
Has anyone any experience or ideas of cause?
Many thanks.

 

[tillergirl]

I think I would start by checking the seating and sealing of the rubber end caps. They are the first thing to keep out sea water in the right place. I am not sure about the sea water circuit being under less pressure than the fresh water side; maybe it is but there is still a fair pressure from the sea water pump.

 

[john_morris_uk]

I had exactly thus problem a couple of years ago. I tried all sorts of things and even set up a pressure test set to see if there was a fault in the heat exchanger stack.

I eventually found the problem; it was a blocked exhaust in injection manifold (mine is a high rise version). Lots of acid baths to clean the blockage and poking about inside it to get the crud out solved the problem. Basically the exhaust was back pressuring the raw coolant side and that got past the rubber seals where the rubber caps at either end of the heat exchanger are gripped onto the heat exchanged stack.

It had got so bad that I had a constant stream of hot water into the bilge from the overflow pipe.

 

[VicS]

I think I would start by checking the seating and sealing of the rubber end caps. They are the first thing to keep out sea water in the right place. I am not sure about the sea water circuit being under less pressure than the fresh water side; maybe it is but there is still a fair pressure from the sea water pump.

Agreed check the heat exchanger end caps, esp the smaller clips clamping them to the tube bundle.

Tube leak in the heat exchanger not likely but not beyond the realms of possibility.

If salt water is being forced in then the pressure may be high due to a restriction in the injection point in the exhaust.

Very strange though that the coolant pressure is retained ... you'd expect it to be lost via " the leak"

 

[fuzzy748]

injection elbow

Hi, i have a 2020b engine and had all sorts of overheating issues and found the problem to be the 'water injection elbow' (the casting at the end of the heat exchanger where the hose joins), the hole where the sea water enters it was completely blocked and eventually i bought a new one after several attempts to unblock it, may well be worth checking

 

[biscuit]

I had the same issue with my VP2020 earlier this season : 2-3 litres of coolant overflowing from a full reservoir indicating a sea- to fresh-water leak somewhere. Having read a very good post here, I disassembled the heat exchanger and exhaust elbow riser, and found .....
absolutely nothing wrong. I put on new end rubber caps and hose clips, flushed the salt water out, and have had no recurrence of the problem. A mystery.

 

[Ruffles]

... I put on new end rubber caps and hose clips, flushed the salt water out, and have had no recurrence of the problem. A mystery.

I did the same. Lasted nearly a year until it recurred.
I think the manifolds progressively rust inside restricting the flow. I took mine to RK marine and compared it with a new one by blowing into the inlet. Now on second replacement in 12 years.
Also, try putting your hand on the rubber boot while reving the engine. You may feel it ballooning.
I now winterise by puring antifreeze repeatedly through the manifolds' jacket via the anti-syphon.

 

[LeonF]

Doesn't explain why the OP's coolant is stil pressurised three weks later, but..I have a 2010B.

I had a bilge full of water motoring back in a very lumpy river at the weekend. Once on mooring and final pump out, all dry. Went back today to find the source. No bilge water. Ran engine in forward and reverse and out of gear, all OK. Dismantled the boat to check anchor locker, cockpit drain hoses etc etc etc . Nothing. Engine had been left running. All OK. Decided to rev engine to max out of gear...water pours out of filler cap tube. Had to be revved to around 3000 for this to start. Bilge filled very quickly. Tightened end caps on heat exchanger. All OK.