Black Radiator Water

[DrDelmas]

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]

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]

Possibly combustion products entering coolant through cylinder head/gasket/block crack?

Hopefully not.

[model 10]

How about rotting hoses?

[gjordan]

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]

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]

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