My truck only.has 140,000 miles on it and this morning when I drove it everything was fine. But about an hour later it was starting to over heat so i parked it and just now had time to look at it and there is a thick black sludge all over the radiator. I checked my oil it was a little low and it was thick as well. I have never herd of this happening before so I'm lost on this one and need it fixed fast.

 

Check under the oil fill cap for any mud-colored build up, white colored exhaust, hard radiator hose, turn your heat on and if it smells sweet it could be coolant. Sounds possibly like a bad head gasket.

 

In the rad or all over the outside ?

 

if you mix the red coolant with the green coolant it turns to sludge and clogs the radiator

 

blue, red, orange, green.... none of them mix... you should always add the same colour coolant...

 

If your oil level is low also, i would bet on a head gasket or if you get lucky, maybe the oil cooler gaskets.

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drain some in a clear jug and let it sit for a couple hours. If it seperates and you have green antifreeze on bottom and bleack oil on top, then that would rule out mixing different antifreezes.