Install a vacuum gauge on the dipstick tube and check crankcase vacuum at idle. Compare to a known good vehicle. If the vacuum reading is lower than the comparison vehicle, visually inspect for oil leaks between the engine and the transmission. Smoke test the crankcase by connecting the EVAP smoke machine to the dipstick tube and inspect for leaks at the rear main seal (this will limit pressure to 2 PSI). DO NOT apply shop air to the dipstick tube or the crankcase. If a rear main seal leak is identified, replace the seal.
