If your oil & your coolant mix together for a while, both sides (the oil system & the cooling system) will start looking like a mint-chocolate milkshake which, as you can imagine, isn't good for anything. Before that happens, though, your coolant will look and smell really oily which is a pretty darn good sign that you've got a headgasket leak.

__________________
Ich muss geisteskrank sein.

The 1983 300 SD: "Old Smokey" (Hilda) Quarter Million Mile Club

The 1986 420 SEL EURO: "¡El Conqístador!" (Helmut) Trunk Triangle Club

The 1995 Cadillac Coupe deVille: "Schlag Kaltluft" (Shaft)