i have a 2004 f,150, it looks like there yellow sludge, like a 'milkshake' in the cooling system. and on the poil fill cap. But whats throwing me off is the oil in the pan is clean. the truck runs great all gauges read perfect, no indicator lights on engine purrs like a kitten, and truck has full power. i cant figure it out, if it was a milkshake i would have problems and i dont, it has been like this for a year since i owned the truck. i had 2 oil changes in the year and both times oil was CLEAN.But that sludge in cooling system and under oil fill cap is what i dont understand having sludge on the oil cap and none in the oil pan. Truck has 107.000 miles on it and runs great. please help

 

Sounds like a head gasket to me.

 

I've read the sludge under the fill cap is from taking short trips and not letting the engine get to operating temperature. I don't think the two are related. Have you ever flush out the cooling system and refilled it to see what happens? Is your transmission oil clean to rule out a broke cooler line inside the radiator?

 

The trans fluid is clean. dipstick clean..I would think if it was a milkshake it would be in oilpan or filter but just did oil change and its clean. I will flush cooling system and see what happens.. thanks