Engine dumping coolant... suggestions please

[Ric]

I am following this thread with interest as my MD2020 did the same on the last two outings after running at highish rpm (above 2500) for a few hours or so.

The first time it happened was after about four hours of running. I let it cool, replaced the coolant, limped home, then stripped the heat exchanger. It was fairly dirty, so I put it down to that.

Unfortunately, it happened again first outing after the servicing. This time I noticed that I had to put back in a lot more coolant than I mopped out of the bilge. I am hoping that maybe there was an airlock somewhere in the system, as suggested at post 39. That would explain why I had to put back more coolant than came out.

 

[Bobc]

The harder you drive the engine, the hotter it gets, and the more the coolant will expand. So you must expect to dump a bit if you drive it harder than usual. Also, an amount of that dumped will have evaporated, hence possibly why you had to put more back in than was in the bilge perhaps?

 

[Ric]

The harder you drive the engine, the hotter it gets, and the more the coolant will expand. So you must expect to dump a bit if you drive it harder than usual. Also, an amount of that dumped will have evaporated, hence possibly why you had to put more back in than was in the bilge perhaps?

Sure, except that driving at 2800rpm for hours on end never used to be a problem.

 

[Ruffles]

A number of people have mentioned salt water displacing fresh. Which could be terminal if undetected.

Is there a simple foolproof way of checking for the presence of salt water in fresh water/antifreeze mix?

 

[Bobc]

A number of people have mentioned salt water displacing fresh. Which could be terminal if undetected.

Is there a simple foolproof way of checking for the presence of salt water in fresh water/antifreeze mix?

But surely if raw water was getting into the coolant, the header tank would remain full, which it isn't.

 

[Ruffles]

But surely if raw water was getting into the coolant, the header tank would remain full, which it isn't.

May not be relevant in this case but it's happened to me a couple of times. Common on MD2020/30 engines. Fortunately it's usually obvious it's happened as the boat fills with warm water! But there's always the wallet worrying suspicion.....

I guess electrical conductivity would be easy as most of us have a multimeter on board. Does antifreeze conduct? Sounds like a little experimentation is in order.