Yes, my truck is a vortec - 305-V8. And I have no choice but to believe the coolant is going somewhere in the motor. BUT - It's been doing this for 10 years now, (I bought it from my Dad who bought it new in '96). There is no water/"milk-shake" in the oil, oil cap, dip-stick. Other than a cool morning like today, (34 degrees right now), no vapor comes from the exhaust pipe. When I drain the oil, it's oil, no water or water/oil mix. I've even left the oil in a five gallon bucket for months trying to see if maybe a little coolant will eventually separate from the oil - nothing. In this truck I use Delo 400 15W40 and change at 5,000 miles. I drive this truck around 12,000 miles per year and most of those 12,000 miles I'm pulling or hauling something. I hate to say "so far so good," but . . . .