I had been using the recommended 5w30 oil when I first noticed the "piston slap" sound in my 03 Trailblazer. I changed to 5w40 to see if it had any effect on the noise; it did not. I returned to the 30 grade and added a bottle of Techron to the fuel tank on occasion, and changed the brand of gas that I was using. Over time the "piston slap" noise has virtually disappeared. Your engine may actually have real piston slap, or some other mechanical issue, but using Techron or something similar might help it the noise is the result of carbon deposits in the combustion chamber.
The thermostat on mine also failed and I replaced it myself. The temperature was still acting strange and it turned out to be the temperature sensor, located on the engine block just above the thermostat. It is such a pain to get to either of them that I recommend that anyone replacing one of them replace the other just to be sure.
The engine has a 7 quart oil capacity and it is unlikely that any sludge developed as long as the oil was changed at reasonable intervals. I suggest using 5w30 viscosity, of the brand of your choice, without any additional oil additives.
The thermostat on mine also failed and I replaced it myself. The temperature was still acting strange and it turned out to be the temperature sensor, located on the engine block just above the thermostat. It is such a pain to get to either of them that I recommend that anyone replacing one of them replace the other just to be sure.
The engine has a 7 quart oil capacity and it is unlikely that any sludge developed as long as the oil was changed at reasonable intervals. I suggest using 5w30 viscosity, of the brand of your choice, without any additional oil additives.
