You coolant enters the engine through the bottom hose. Is kept in the engine until heated up to the thermostat setting (degrees), the thermostat opens and releases the water into the radiator though the top hose.

I suspect that your radiator is the culprit since there is no oil in the water or vice versa.

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1986 Euro 500SEC "RUF" 9:1CR, "Rose"
1985 Euro 500SEC Cabriolet AMG Widebody
1982 Euro 500SEL "Blue"
2001 Texas Heeler (Aussie/Queensland X) "Sulphie",
2012 Queensland Red Heeler "Squeak"
Best dogs I've ever had.