It1s10---I tried the test you suggest. If I run the engine with the dipstick tube blocked off, and the oil filler cap removed, it will "suck" enough at the oil filler cap hole in the valve cover to hold a peice of paper in place over the hole, although I think it must be very little vacuum, because with the paper "sucked" in place over the filler cap hole, if I unplug the dipstick tube and put the vacuum gauge on it, it isn't pulling enough vacuum to register on the gauge.