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5w20 seems like it is too thin an oil for the 5.0l especially when considered the only recd weight worldwide under every condition. i have my doubts with its performance when it gets hot or under long periods of moderate to hard accelleration.

i have been thinking of trying 0w30 or 0w40.

Does anyone have experience with weights other than the reccomended 5w-20?
 

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There is a lot more to oil viscosity than most people think. There are a couple reasons why manufactures are going with 20w oils. One is more fuel economy because it takes less power for the oil pump to pump a thin liquid. But this is not the only reason. If the engine is properly designed to use a thin oil there is no benefit to a thicker oil. People seem to think a thinker oil protects better but this is not necessary the case. In example in a high revving engine where a lot of heat is generated in the rod and main bearings a thin oil at the same pressure as a thick oil will flow more oil through the bearing carrying away more heat. since these are under pressure the oil viscosity has little to do with the protection because it is the oil pressure that supports the bearing not the oil viscosity(one notable exception is top fuel nitro drag engines but we wont get into that here). So in an engine with a big oil pump and tight bearing clearance a thick oil can hurt the engine. The other thing to consider is if you have Variable valve timing or a multi displacement system they uses the oil to activate these systems and are calibrated for the thin oil(ie dodge 5.7 Hemi with MDS must run a 20 weight for it to work correctly). There is a lot more to this but it gets really complicated and would be a 10 page post.

But on the same token some manufactures spec a light oil with no changes to the motor to get that extra .5mpg for a better fleet gas mileage, In that case i would go to the a heavier oil. So the best answer i can give is it depends. based on the fact the 4.2 is very similar and specs a 5w30 or 5w40 for hot climates i would think you would be ok with a 5w30. But if there are no problems with a 20 weight i dont see a problem sticking with it. Also you can have a used oil analysis done by Blackstone labs and run a 20w and then a 30 weight of the same oil like Mobil 1 and compare the wear numbers and that will tell you which one your motor and driving style prefer.
 
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