I have a 1995 3.1 v6 Lumina which is losing a lot of anti-freeze. I fill it up then in a 15 mile trip its low again. There are no visible signs of leaking. There is weird smoke from the back or anywhere. The oil is not a milky color. My heater works the same. So where is the anti-freeze going?

Oh its not over heating too.

Check the rad cap as it may be leaking when under pressure...how much coolant are losing?

I agree with the radiator cap being the cause

My own car had a wee small head gasket leak going to the number 4 cylinder and never showed over heating or oil in the water but i was loosing water
when the head got hot the leak took up

Until the gasket blew and thats when we found the top of the number four piston was bright green :grinyes: