So we've been having pretty nice weather here in MI. I have a 72 Mach 1 with a 351C that was freshly rebuilt last year and has about 100 or so miles on it. I went to get it out today. When I opened the radiator cap, I have a ton of brown clay like sluge in it. It is an aluminum radiator. I checked the oil on the dipstick and it looks normal. Not milky at all.

Is this from a blown head gasket, or just from the antifreeze reacting badly with the radiator?

 

What antifreeze did you use? I dont have anything like that in my aluminum radiators, or in the copper ones. I remember something like that happening when the green stuff is mixed with the red stuff, or in more proper terms glycol mixed with dexcool.

Yeah the weather is nice for March/April UP here, usually we are still buried in snow and I already have the drag car running and ready for updates. Probably going to work on the truck today though, it needs some attention. I wonder if we will get another blizzard this month, we usually do.

You gonna bring it to St Ignace in June? Im thinking about heading over there with something. We really need a cruise or car show in Marquette, lots of car people up here but nothing to do with them. Woodward is a bit far to go for a crowd of that size and watching minivans and stuff go by instead of machines and rods.

 

If your worried about blown head gasket a simple compression check will show it.If that all is normal flush the radiator it should be ok.

 

I've seen this on mine, no leaks but the radiator fluid went bad. How long has it been in there? I suggest flushing the cooling system.