Anyone know why oil was changed from 10w 30 for 04's to 0w 40 for 05's and later models?
Main bearings changed from 120 degree in 92-04 to a 180 degree in 05+. 180 degree mains allow for better transfer of the oil from the block to the crankshaft oil journals, increasing the oil flow to the rod bearings. On the downside, increasing oil flow also lowers the oil pressure at low engine speeds where the relief isnt actively venting.
Couple the large number of bearings in the Viper engine with decently large oil clearances, a pump that is borderline too small and 10W-30 oil which is pretty thin at high temps, and you have an oil pressure problem when not using 120 degree "restrictor" main bearings that keep flow in check. However, as proven time and time again on SRT-10's, oil flow to the rods should not be a compromise!
As a temp fix without having to make any other changes and to keep the engine in a normal operating pressure range, the solution at the time was to bump the Viper to 0W-40, being a heavier weight oil it remains thicker at higher temps keeping flow rates in check, and also protects better with a thicker oil film, an added bonus. Being a 0W cold oil, it also doesnt have a cold pumping down-side to its use. Even with this change however, 05-06 cars STILL see a drastic pressure drop at idle compared to earlier cars. 04's see about 50 PSI hot idle, and 05-06 sees about 25-30 PSI with their respective OEM fills.
In 2008 to combat this issue, on top of needing even more oil flow because of the cam, the oil system was completely revised, including a 20% larger oil pump.
Ultimately, 0W-40 is a better oil for the Viper application. It has better high temp and low temp properties, offers more protection, and it better suited to the clearances the Viper engine uses in most cases. Why didnt they use 0W-40 back in Gen-1/2? I dont think it was available yet honestly, and it was just left alone until it eventually became an active issue.
