Carbon Buildup In Cylinder Head

[joelittel]

Ok, thanks. I had no idea that I'd been using the wrong stuff. Darn it.

[joelittel]

Thanks to all who helped with this issue. Without your input I would have continued using green antifreeze and eventually ruined my engine. Hopefully I haven't caused any serious damage already.

Is there a recommended cleaning method?

[RRoller123]

I think I have the green stuff in there too. But the block is iron.... ? Is the problem that the green attacks Al? I am pretty sure the jug says it is safe for Al, but I will have to check.

[joelittel]

Last night I checked my new-to-me block and it has the same type of corrosion in the coolant passages. I'd bet many Spiders have the green stuff running through their veins.

[So Cal Mark]

green coolant (ethylene glycol) is the recommended coolant for your Fiat. Corrosion in the aluminum water passages is caused by electrolysis. Once the coolant breaks down, usually when it's over 2 years old, the cooling system starts generating voltage which accelerates the corrosion.
From Wikipedia;

commonly used in liquid-cooled automotive and industrial combustion engines, ethylene glycol is also used in most common heating and cooling systems in houses and commercial buildings. The ethylene glycol antifreeze used in automotive applications should not be used in the heating and cooling systems of buildings, however, due to the containment of silicates that are mixed into the automotive antifreeze. The silicates are added to the ethylene glycol antifreeze mixture to combat corrosion in aluminum engine components. It is also imperative to avoid using city tap water in any ethylene glycol antifreeze mixture since many city water supplies are treated with chlorine, which is a known corrosive.

[RRoller123]

Excellent, thanks for clearing that up, and lowering my blood pressure at the same time.

[djape1977]

and again, talking from my experience as a mechanic working on classic fiats for over a decade, use g11 and g12 coolant, meaning blue and pink stuff.
avoid green as it eats away at aluminium alloys.
i don't know what's the policy on coolant colour in US, but in europe they're colour coded, so if you use pink stuff or blue stuff, you know what you're getting.