Check the cap. Have it pressure tested. If it's weak, you will lose coolant thru the overflow hose. Don't know the exact spec but something in the range of 17-20psi or about 1.2 bar. Otherwise it's getting consumed inside the engine which reads as head gasket. Could be getting into the sump or a cylinder. Drain the oil, see what you get. Pull the plugs and get someone to read them for you..

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE