Soot in radiator, is it what I think?

[Ken Wells]

450C, have been having to add a little coolant along, really hasn't had me too concerned but I've noticed what looks what I first thought grease but now I believe is soot that accumulate on the bottom of the radiator cap. Motor runs on the warm side of normal but starts instantly and seems to have plenty of power. No coolant in the oil.
Head gasket?

[LeonardL]

Well this doesn't sound real good. Usually if it is a head gasket it will be blowing exhaust gases into the cooling system and then shows up in the radiator as bubbles and suit. It will also force your coolant out of the system. There are kits available for checking your coolant to see if exhaust gases are getting into the cooling system. I got mine from NAPA although that has been a few years ago.

If this substance appears oily it could be the engine oil cooler leaking oil into the coolant. It won't always show up in the crankcase because your engine oil pressure is higher than the cooling system pressure.

[Ken Wells]

Well this doesn't sound real good. Usually if it is a head gasket it will be blowing exhaust gases into the cooling system and then shows up in the radiator as bubbles and suit. It will also force your coolant out of the system. There are kits available for checking your coolant to see if exhaust gases are getting into the cooling system. I got mine from NAPA although that has been a few years ago.

If this substance appears oily it could be the engine oil cooler leaking oil into the coolant. It won't always show up in the crankcase because your engine oil pressure is higher than the cooling system pressure.

Doesn't look or feel oily, just black soot.