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DrDelmas 28-05-2016 13:47

Black Radiator Water
My 1985 Onan GenSet with a Cummings engine turns the fresh water in the cooling system black. I have flushed it 5 times and the water still is not clear. It appears to be very fine particles suspended in the water that will not fall out. I noticed this last year and again this year when I changed the coolant. The engine coolant level stays constant all year and the engine is used all year as we are full time crusiers. Any ideas?

boatpoker 28-05-2016 14:27

Re: Black Radiator Water
If it's not oi and "particles" suggests not. My next guess would be very active corrosion and I'd suspect you are about to deal with a significant issue if not addressed.

senormechanico 28-05-2016 14:45

Re: Black Radiator Water
Possibly combustion products entering coolant through cylinder head/gasket/block crack?

Hopefully not.

Ecos 28-05-2016 15:39

Re: Black Radiator Water
How about rotting hoses?

gjordan 29-05-2016 09:16

Re: Black Radiator Water
Get one of the automotive radiator testers and see if excess pressure (even a little excess) is building up in your system. You may find you have a small head gasket leak allowing gasses into your cooling system. Small leaks usually get bigger. Good Luck. Grant.

Glenn C 30-05-2016 02:28

Re: Black Radiator Water
Hi there is lot of info on the automotive forums....typically indicates hose failure. If oil was getting in through a damaged head gasket, then the water is likely to be a creamy colour rather than black. Are there other symptoms ? Among other things, white exhaust smoke can indicate a defective head gasket.

DrDelmas 30-05-2016 08:37

Re: Black Radiator Water
Thanks for the advice, will pressure test but suspect the hoses. I have no idea how old they are.

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