Sea water in cooling system

[DrBob]

Any one got any ideas on an engine cooling problem. Volvo will be fixing it under warranty (as they are already working on a fuel problem!).

The engine is 6 month old Volvo MD40. Today I noticed that while running it hard (2,700revs / 6.5knts) there was a constant flow of water coming out of teh coolant overflow at the top of the fresh water header tank. Not sure of flow rate, Maybe 100ccs in a few minutes, but the water tasted of salt. Obviously water is getting from the sea water side of the cooling system into the fresh water side. There was no trace of antifreeze - must have all been washed out.

I suspect this has been happening since the boat was new in Julyl as we have had water in the bilge that I have not been able to work out where it was coming from. I check the water level every week in the header tank and it has been fine -hence never really looked closely until today.

Any ideas what sort of thinks go wrong on a brand new engine. It would be useful to know a bit more about this when the Volvo guy is down.

Dr Bob

 

[pete]

Hi DrBob

Don`t know this engine but it sounds like the colorifier is leaking internally.

Pete

 

[Heckler]

as a rule of thumb, seawater in fresh water circuit goes across thru a leak in the heat exchanger, i dont know your engine but make sure the engineer checks the exchanger hasnt got a leaky tube or face. on the smaller volvos the exchanger is held in place with hose clips holding a "top hat" onto the exchanger and the raw water intake, if this is the same system on your engine a badly placed exchanger tube bundle or poorly clamped top hat will alllow water to pass across. other puzzling thing is the steady flow of water out of the over flow, the rad caps are usually set at about 7 psi and i am not sure what pressure your raw water pump can put out. if it is less than the pressure where the cap opens then you could have a prob with leakage from head gaskets ( the only other place where you can get enough pressure to open the cap.) however head gasket leakage would not cause the symptoms you have unless you have two distinct issues, i.e leaking gasket and leaking exchanger together. ask the questions however. also would be extremely concerned about raw water slushing around the inside of my brand new fresh water cooled engine for a season. would push for an engine exchange if i was in your position!! ok if it was a second hand one and i was paying would go for a thorough flush etc BUT that is up to you
stu

 

[Ruffles]

Same thing happened to my 2030. The heat exchanger elements are rather too short for the box leaving insufficient tube for the rubber boot to grip. It then slips away from the 'in' end. You can feel the tube under the rubber by squeezing it. Compare each end and it should be obvious if it has moved.

 

[DrBob]

Skipper-Stu and Ruffles

Thanks for the replies. I hadnt realised there was a tube with jubilee type clips separating the sea and fresh water sides - so it sounds like a fairly simple job. Ruffles - how do you get access to the tube to feel if it has slipped off? Can you do this from the outside? I was dreading a mechanical failure in the block.

I am a bit concerned about having salt water in the fresh side for 6 months. Any thoughts on what damage that may have done and is it possible to flush it with something that will passivate any rust formed.

The water is coming out at a steady rate but I am pretty sure it is not the head gasket as there is no oil in the water etc

Hopefully Volvo will be out very soon in the new year to sort it.

Dr Bob

 

[fisherman]

Warranty? Don't even touch it , give it back!

 

[Ruffles]

DrBob,

You should be able to feel the tube end by squeezing the end of the rubber.

If after realigning and tightening the clips it fails again then you may have a constriction somewhere causing excess pressure.

Why not leave it to the dealer? Any opportunity for harumphing at Volvo Penta should taking IMHO /forums/images/graemlins/wink.gif

 

[Guest]

Anti-freeze has corrosion inhibitors - so a real good flush out with fresh water, drain off, flush again, drain off ... then refill with water / anti-freeze mix should be ok ....

Remember that the difference between many raw-water cooled and heat-exchanger engines is basically the heat-exchanger and fresh-water ......

 

[VicS]

Another difference is the temperature at which they run (determined by the thermostat)

Salt water cooled engines run at a lower temperature than fresh water cooled engines. This means that a normally fresh water cooled engine which has been run on sea water is likely to have suffered higher corrosion and scaling levels than an identical engine set up to run on sea water. The actual extent will of course largely depend on the actual running hours since the fresh water and its inhibitors was displaced.

A seawater cooled engine is also likely have anodes fitted to control the corrosion but that would not be necessary in an indirectly cooled system as the corrosion inhibitors in the antifreeze would do that. So that protection will presumably not exist either.


It's a nice idea to try and get a new engine under the warranty but I would not put much money on the chances of success. They will fix what's wrong and if it all then works that will be that. Wouldn't you?

I was thinking about the question of the pressure on the sea water side of the heat exchanger being higher than that on the fresh water side. I wonder if that is deliberate so that in the event of a leak between the two seawater replaces the fresh instead of the fresh simply being lost and eventually perhaps leading to the engine overheating due to lack of primary coolant. It's just speculation, a dangerous thing I know.

It would be wise though to check that there is no restriction to the seawater flow after the heat exchanger. Presumably there is just some hose and the exhaust cooling injection point.

 

[Heckler]

dr bob
be careful about mine and ruffles explanation, we were using our engines (vp2030) as an example, as i stated i havent worked on an md40 so dont know the definitive, it will be similar but not exact so be carefull if you start prodding around OR try to bullshit the engineer!
VicS has given a good explanation of the pros and cons of running seawater in the fresh water side. i would really push for an exchange, nothing to lose! if the engine has been like that from new someone wants their arse kicking cause they are supposed to "commission" it.

 

[DrBob]

Thanks for all the replies guys. I will let you know the outcome once Vovo have had a go!

Dr Bob