Black deposit in header tank

[Carduelis]

I was checking my antifreeze and noticed that the water has a black carbon like deposit in it.

Any idea what this might be?

The engine is a Volvo 2040 BTW

 

[savageseadog]

You'd better hope it isn't a head or head gasket problem.

 

[pheran]

Any pressure building up in the header tank? Or sign of bubbles? Both those could indicate head problems. However, I had just that problem with a Volvo TAMD41 earlier this year. Turned out to be the internals of the engine water pump shredding themselves and had apparently been doing so for some time although in near total silence. Confirmed when the seals then gave way. Little bits of metal everywhere!!

 

[Carduelis]

Yes, a head gasket problem is what I'm afraid of. The oil seems clean enough though. I'm assuming that you would see the same sort of "mayonaise" as in a car engine if water was getting into the oil...?

If the heat exchanger was corroding internally would it show up like this?

 

[savageseadog]

I was thinking of the exhaust blowing into the cooling water

 

[milfordman]

It is posible to have the head gasket fail so that the cylinder gasses are blowing into the water without the water geting into the oil so the oil will not emulsify in that case. If this is the case then running the engine with the radiator cap off will usually show bubbles in th cooling water, also the water level will some times change wih the revs. I.E Revs higher- water level up, : Revs dropped- water level goes down.

 

[pheran]

Agreed. It only needs a tiny crack in the gasket or the head, not big enough to allow water to seep through but opens up under heat or pressure to let gasses escape into the water jacket. If it is a crack or faulty gasket in this case, must be very small otherwise water loss caused by the pressure would have been noticeable by now.