Run the engine for several minutes at idle. Turn the engine off and let it sit for about 15 minutes. Restart the engine and immediately increase the engine speed while observing the exhaust. If a heavy billow of bluish smoke is exhausted then disappears and the exhaust remains relatively clean, the most likely cause is excessive valve guide wear. In this case, the valve guides or valve guide seals require service. If the above test only produces mild smoke and the smoke remains at the same level during all operating conditions, the piston rings will have to be tested. This is done by performing a compression test on the engine. The first test is referred to as a “dry test” and the second test is referred to as a “wet test”. The dry test consists of measuring the engines compression using a compression tester installed in the spark plug hole and the ignition system disabled. The engine is then cranked and the pressure is measured and recorded. A few teaspoons full of oil is then poured into the spark plug hole and the compression is then measured again. If the reading increases more than 15 PSI, the rings are worn and major engine service is probably required.
The other test you can try is taking your car up to 50 mph on an open stretch of road, take your foot off the accelerator, allowing the car to slow down to around 10 mph, and then accelerate suddenly at close to WOT. Have someone in the back seat, or leaning out the window, or at the side of the road observe for blue smoke. Safety first when doing this.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)