Oil: Conventional vs. Synthetic Blend vs. Full Synthetic
 

Okay, so my car takes 5W30 oil. That's what Toyota recommends in the owner's manual. What is the difference between using conventional, synthetic blend, and full synthetic oil of the same weight and viscosity (5W30)? Also, would there be any benefit or harm in using 0W30 instead of 5W30?

You can do extended drain intervals with synthetics, that's the main advantage.

The 0w30 will only give you an advantage when the engine is cold, else it's the same viscosity. You should try 5w20 or even 0w20 instead.

The secondary advantage of synthetics is more stable viscosity at low temperatures. Which in a cold climate translates into easier starts & better efficiency but only while the engine is coming up to normal operating temps. The actual fuel economy gain in that scenario would be tiny, though.

It's worth noting that no major motor oil company (that I know of) claims "improved fuel economy" as one of the benefits of its synth motor oils relative to the same weight non-synth.

Mobil 1, IIRC, basically says that their 0w30 is more stable than, but has close to the same viscosity, as 5w30, but does claim increased fuel economy, by up to 2%

M1, unfortunately, is the only producer I know of that makes 0 weight oils, so the comparison has to be made with 5 and 10 weight oils, which kind of skews the result. Then again, the engine only sees that weight when it's cold, and based on normal driving tests, it's only cold a few mins, so maybe the higher hot-engine stability attributes to the better FE, in which case, it's an even test with any hot-30 oil.

Thanks for the replies, everyone! I also just found a Toyota Service Bulletin stating that all 2006 and 2007 model year vehicles with certain engine types (NZ series is included, which is what my 2007 Yaris has, the 1NZ-FE engine) should be using 5W-20 oil instead of 5W-30. They say it offers better fuel economy, engine protection, and increased cold starting performance. My oil cap and owner's manual say 5W-30, but that could be because they were printed before the bulletin came out. The bulletin has a date of March 29, 2006, and my car is a 2007, but I know that the model year always comes out the year before, so my 2007 Yaris was available in 2006. This means it was probably constructed in 2005 and the owner's manual was printed in 2005 or early 2006, in which case this bulletin hadn't been released yet.

I think I'm gonna bring a printout of the Toyota service bulletin to Valvoline next time I'm due to have my oil changed there. I'll ask them to use 5W-20 instead of the 5W-30 they had been using.

If you want to check out the bulletin, it's Toyota Service Bulletin EG018-06.

I am an overworked expert on this subject. :rolleyes:

conventional is good for older, especially inline and older, let the valve seals get their burnable drips.

syntec blend is somnething most can get away with, any year.

full synthetic can go to most all aluminums..old irons hate it however, it is a long stinky road on the old irons...and it may even fail with it.

today, go for oils at manufacture date, most if not all the gassers can take anything...of course synthetic is amazing, get the right ratings for your car, and even beyond. 20 years old or so, you have to look up your cars humble demand.

There is a study in your list, Tasdrouille, that shows an advantage for synthetics in a diesel engine.

http://me.engin.umich.edu/autolab/Pu...e/P2002_03.PDF

It's small (10% less friction for the best synth over the base non synth) but every bit counts. This study does not test for cold performance which possibly would give greater returns.