Volvo Penta MD22 - What is coming out of the coolant expansion tank?

[andyp]

Following Loopy's excellent post on learning from experience, I need some advice following our first trip of the year.

Gosport to Bembridge (actually anchorage off Seaview) and back last weekend.

Initial departure abandoned as oil pressure dropped quickly to zero and warning light came on. Amazed to see oil filter split and oil spraying into engine bilge! After limping back, closer inspection revealed a leak on one of the calorifier hoses had been dripping hot coolant onto the oil filter (presumably for some time) which had corroded the filter casing. Re-made calorifier hose and replaced oil filter (great service from Arthur's Chandlery on Easter Saturday). While replacing filter I realised the other calorifier hose was not great, so cut an inch off the end of that hose as well and reconnected.

Second departure much better with oil pressure where it should be. Unfortunately the coolant (which I had diligently refilled) now started pouring out under the expansion tank cap, even at 1,200 rpm. I placed a bowl under the expansion tank and completed the trip, emptying the bowl every 15 minutes. As time went on the leaking coolant changed from dyed to clear, and got hotter, though never hotter than hand-hot. I didn't have the guts to taste it but my money is on raw water.

So, the boat is now back on its berth. I have a new expansion tank cap, heat exchanger end caps, exhaust elbow and coolant on order. I think I have raw water from the heat exchanger over-pressurising the coolant side together with a blown expansion tank cap (the first leaks appeared when the coolant was only lukewarm.

It could also be a pinhole in the calorifier pressurising the coolant side from the FW side but the FW pump was not cutting in excessively. I will clamp the calorifier hoses and test run the engine to prove this is not the issue.

I may also have a partially blocked exhaust elbow raising the raw-water pressure.

Contaminated water/oil in the bilge has already been sucked out and bilge cleaned while the bilge pump was isolated so no contamination overboard.

I think I have read enough of Skipper Stu's comments about the cooling system on these engines to have a good idea where to look next but, as always, any advice would be welcome.

 

[NormanS]

Sorry, can't help. I think you have covered the possibilities, and having the same engine, I'll be interested in what you find. Good luck, and hopefully not serious.

 

[scottie]

Possibly an airlock?
Water not circulating

 

[vyv_cox]

If it was a pinhole in the calorifier heating tubes the coolant would be diluted by fresh water even when the engine was stopped provided the domestic water pump is on. When I dealt with this a few years ago for Carmel2 we just took a hose off for half an hour and the problem was obvious. Written up in PBO maybe 6-7 years ago.

In theory the coolant pressure is always greater than the raw water pressure but in the past various similar cases have shown that a blocked injection elbow can raise the raw water pressure sufficiently to blow water past the heat exchanger seals into the coolant. Of course if the pressure cap had failed/was weak this would happen more readily.

 

[Yngmar]

Blocked injection elbow is a good candidate, easy to check/repair and much better news than the aluminium heat exchanger having corroded through, which is a well documented thing on the MD22 if you're not very careful.

Raw water in the coolant would explain why it corroded the oil filter at all - normally coolant shouldn't corrode anything it drips on, being made of glycol, anti-corrosion additives and distilled water.

If it's just the injector elbow (take off and clean/replace the bit of hose leading to it too), then celebrate and also flush the heat exchanger through thoroughly to remove any salt before refilling with coolant.

 

[andyp]

Think I have sorted my coolant leak issue.

The exhaust elbow was definitely blocked, resulting in back-pressure on the raw water side.

The heat exchanger tube-stack had some broken connections at the pipe ends.

So yesterday I replaced the exhaust elbow and injection point. I had the tube-stack repaired for a reasonable price by Abbey Heat at Eastleigh. That went back in with new rubber boots and a (pricy) rubber sleeve, making sure the tube-stack was precisely centred in the heat exchanger body. Also a new temperature sensor and thermostat, plus expansion tank cap.

All filled with 8L of newly mixed coolant and test run for 30 minutes.

Minor leaks at first which just needed the jubilee clips nipping up. Just one very slow leak to find now, somewhere under the thermostat.

Definitely holding coolant pressure and level, and I now have a temperature gauge which moves. Good flow of raw water. IR thermometer readings of different parts of the engine look good. I wasn’t able to run it up long enough for the thermostat to open, as I had to get to The Stoop for Quins v Leicester, but I will do that next time I am onboard.

Old exhaust elbow is in a bucket of Rydlyme and should be recoverable as a working spare.

The refurb took a long time but that was mainly trying to line up all the pipes, hoses and rubber boots. Worst moment was dropping the loose section of the exhaust hose clamp down the exhaust pipe!! Luckily it was magnetic so I could reach it with my magnet-on-a-stick...

Thanks as always to all for advice and suggestions.