When the oil is wormed up in 5W-30 and in 10W-30 they are both 30 wieght oils. The difference is when the oil is cold " like it is on start up " you want the lighter cold wieght oil for maximum protection on start up, because that is the time in witch most of the wear on the engine occurres, and the 5W-30 helps to minimize that wear on start up, and thats why the factory wants you to use it.

 

That's exactly what I told the technician at my dealer! He said since south Texas is so warm in the winter (right!) the thicker oil would stick to the metal surfaces longer than the thinner oil and protect the engine better. This sounds like a Catch-22 for the oil companies...

 

The only time the oil has a problem being pumped up on start up is when the temperature is low, as in 35 degrees or lower. That is why my R/T gets 5W30 Mobil 1 in the winter and 10W30 Mobil 1 in the summer and my Roadrunner gets 10W40 Castrol GTX in the winter and 20W50 Castrol GTX in the summer. As the technician said, the thicker oil is better in warmer weather because it stays on the parts better and the oil is at a warmer temperature so it will pour/pump up well, but in colder weather the thickness causes it to pour/pump up slower which is not good. <img border="0" src=smileys/smiley2.gif border="0">

 

Yeah, it doesn't get below 35 degrees here very often and my SRT-4 stays in a closed garage at night, so I guess the service tech was right. I've never used a "thinner" oil than 10W-30, syn or otherwise, and haven't had any engine problems in any of my cars in almost 40 years...<IMG src=smileys/smiley4.gif border="0">

 

Folks, </P>


Issues about the cold start benefits of the different weights aside. If you read the notice for the manual, it clearly states that the change is due to the fact that emmisions testing was done dino 5W30. Therefore they cannot by law recommend the use of any other oil. </P>


It'</P>