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Lost MPG switching to this oil weight.


Topic starter


I have a 2016 Acura RDX with 100050 miles on it and bought it with only 3,000 miles in 2017. I've always had the dealership change the oil where they were using OW-20 weight as recommended by the factory(also in the manual). Miles per gallon were nearly 26 with the oil the dealership uses. I was hearing on the radio about how better it is to use AMSOIL in the engine and decided to try that. The mechanic I emailed informed me to NOT use the OW-20 weight but use the OW-30 instead. Something I noticed after is that my miles per gallon have gone down to 24 from the 26 mentioned above and I believe it has to do with the weight of oil(OW-30)that's being used instead of the OW-20 from before. Can this weight have anything to do with the lost of MPG and would it be more beneficial for me to go back to using the factory recommended weight of OW-20 in AMSOIL?

Thank you for your response. 

4 Answers

Engineers design your engine to run best on a certain oil and viscosity. 

Sure you can add whatever oil to your car,  but doing so can potentially compromise it’s efficiency and/or longevity. 

Think about it, 0W-30 has a higher viscosity than 0W-20. Higher viscosity means harder to flow. Harder to flow means more friction. Harder to flow means it can’t get to the nooks and crannies of the engine as easy. Harder to flow implies less protection for your specific engine. 

For some engines, 0W-30 might be perfect. And 0W-20 might be too flowy.

it’s always best to use the oil recommended in the owners manual. 


Maybe.  That small of a change could be due to any number of things, including seasonal factors.  To confirm that small a delta you would need to do rigorous testing, involving multiple similar vehicles and multiple randomized oil changes.  But as @kaizen said, it is certainly plausible.

Amzoil is perfectly fine.  But go with the spec weight.

Welcome first time poster...


Most cars get a couple less MPG in the winter - warmup lasts longer and uses more gas, cold is is denser and thus has increased aerodynamic drag.


Topic starter

Greatly appreciate all of your responses and advice. I will go back to the 0w-20 as recommended by the factory and see if the MPG's change. Thanks fellas! Happy