I have a 2002 Dodge RAM Pickup owned since new now with 120K miles, I also have a 2005 Dodge Magnum 5.7L HEMI with 57K miles also owned since new. Both of these vehicles have had lifter noise early on within the first 20K miles. When I first noticed it with the RAM Pickup I thought of changing the weight and type of the oil to a heavier weight from the recommended 5W-20 the factory recommends but I decided against it since the warranty might be violated if I changed it. So I decided to continued to use the 5W-20 Oil until the warranty was off.
I actually continued to use the 5W-20 oil past the warranty period of 36K miles until one day I noticed that the lifters were rattling when I started the Engine and that it continued to rattle for several minutes until the engine was warmed up. It was time for a oil Change anyway so I decided to change the oil and this time I had 10w-40 put in. I immediately noticed a difference in the sound of the Engine, the rattling lifters sound was gone. Even after 1500-2000 miles on the fresh oil there was virtually no rattling lifter noise. Especially on Engine Start-up when I would hear the most lifter rattle noise in the 5.7L HEMI in the Magnum.
This made me wonder what was going on with the 5W-20 Oil and why would it appear to break down so quickly that the lifters would rattle so much. I began to search on the web for 5W-20 oil to see if others had a concern about this oil too. What I discovered was that there was more information regarding the purpose of the 5W-20 oil than I thought. Almost every article and white paper I found reported that the real purpose of the manufacturers recommending the light weight oil like 5W-20 and 0W-15 was so that the overall fuel mileage of the manufactures engines could gain a higher rating. Most applications of the light weight oil was so that the major Automotive Manufacturers could gain the increase fuel mileage rating without making significant changes to the Engine designs. It does this by reducing the flyweight resistance on the rotating components of the Engine and not necessarily reducing surface contact friction on items like the Pistons, Rings and Lifters to the Engine Block cylinder walls. In addition these articles point out that the consumer does not have to use the manufacturer recommended 5W-20 weight oil to maintain the warranty on their engines.
After I read about this fairly significant revelation of what I would consider “Engine Early wear from light weight oil” I decided to change the weight of Oil in the Magnum right away while I still could save it since it had only about 30K miles. So I immediately had the oil change done to the Magnum 5.7L HEMI and had 10W-30 Oil put in. I got a lot of funny looks and questions when I asked for this change. The HEMI 5.7L would always exhibit Start-up Lifter Rattle after the engine would sit overnight. It sounded like the lifters were actually moving with no oil in them at all, and it probably was since the light weight 5W-20 was most likely draining down out of the engine and into the pan overnight. The rattling would last for only about half a second or so but it was so harsh sounding that it always bother me. The Next day after the fresh oil change and sitting overnight I listened very carefully as the engine was started, listening for that same lifter rattle that it always had since new, but this time there was nothing not even a hint of it. That was more than two years 20K miles ago and still today even with 3K miles on the oil change it doesn’t make a sound on Engine Start-up. I now use 10W-30 or 10W-40 weight oil on all my vehicles. Also, I do not use Synthetic, but I do change the oil at 3K miles.
The Truck has 120K miles and the Magnum has 57K miles both run smoother than when new and still get nearly the same fuel mileage as when new and neither has any lifter rattle or ticking.
I've heard the 5-20w claims for mileage increase but wonder if it really makes much difference, sounds like it's a minimal gain from your experiences. I am surprised that changing to a thicker oil doesn't void the warranty. They usually try to find any excuse to get out of a warranty claim.