I read some threads in another forum where some posters claim piston slap occurs when going from 5W20 to 5W30. Apparently it only happens in cold weather and eventually goes away when the engine warms up. They said that the piston slap goes away when they reverted to 5W20. I'm curious about why there would be piston slap since both oils begin at a viscosity of 5 when the engine is cold. They were old threads so they were talking about relatively new engines. Is my understanding incorrect?
Well the one is a little bit thicker than the other and I'm called startup to lubricate correctly that's the problem. Why mess with success keep the suggested oil in
Because the thread began with a long winded explanation of why the 4.6L should be using 5W30 like it did originally but Ford changed it to 5W20 to meet CAFE standards. It was mentioned in the thread that the oil change resulted in a minuscule savings in gasoline (less than 1%) but results in much less protection of the engine (about 30% less). People would rather their engine last longer so a lot of Mustang owners went to 5W30 while a few complained of piston slap.