13 mpg decrease after mods possible or most likely just a mistake?

[SentraSE-R]

Caveat emptor. Toyota didn't OK 0W-20W oil in its engines until 2006. You risk damaging your engine when you run thinner viscosity oils in older engines. I suspect they don't have smooth enough bearing surfaces to get adequate lubrication with the thinner oil.

[Ryland]

Any reason not to get a Scan Gauge? it will not only tell you what your real time mileage is and your trip mileage but it will tell you the read outs from all the sensors so you can see if there is something wrong.

[AaronMartinSole]

Originally Posted by SentraSE-R

Caveat emptor. Toyota didn't OK 0W-20W oil in its engines until 2006. You risk damaging your engine when you run thinner viscosity oils in older engines. I suspect they don't have smooth enough bearing surfaces to get adequate lubrication with the thinner oil.

I would rather hear a position that supports me using 0W-20 because this position does not please me. Anyone? Just kidding. I don't really know the differences at all or the pros and cons between different oils, just thought 0W would be the best on gas. I've seen AMSOIL tests and charts showing that they're better for the engine and prevents wear as well. What do I do now?

[MetroMPG]

You can have oil analysis done after a while if you're worried about it. It will tell you whether there are elevated levels of metals in there. I'd be surprised if it's going to be an issue.