I have a 1996 Lumina with the V6 that is losing coolant somewhere but no visible leaks. Today the low coolant light came on so I added some coolant to the overflow tank. Later on in the day I noticed the temp. gauge started rising but then go back down. It repeated this cycle of heating up & cooling down a couple of times before I got home but never overheated. When I got home I noticed no leaks of any kind but my when I checked my oil dipstick I noticed the oil seemed like the color of milk choclate & was about 2-3 quarts over the full mark. Is this a head gasket problem or something else? If this is a head gasket what can I expect to pay for a repair? Mechanic rates in my area run $55-$65 a hour. Thanks.