Car Court

Posted by acroy (A) on May 31, 2012 at 13:29:16

In Reply to: RE: What's the word on sythetic oil? posted by albee33 on August 14, 2004 at 22:41:24

Full synth is the way to go. Only exception would be if the motor is already in poor shape and is drinking/leaking oil already.

For a starter, read http://en.wikipedia.org/wiki/Synthetic_oil
For an oil-head analog of the Asylum, venture here: http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=cfrm

Note only group 4 and 5 are ‘true’ 100% synthetic. 1-3 come from mineral oil and are inferior. Check the bottle! Synthetic blends are a waste of time as far as I can tell.

The limitations of dino oil are becoming more apparent. I have run into 2 specific examples, both are well-known on the respective forums:

• 2.0 liter 4cyl in Mazdas have delicate oil control rings grooves in the piston. At about 100k miles on conventional oils, enough sludge has built up to prevent the oil control rings from seating properly, causing smoky start-ups and high oil consumption. A cleaner followed by switch to 100% synth can sometimes reverse the issue. Only other alternative is an engine rebuild.
• Late model GM V8’s with cylinder deactivation have similar issues on the deactivated cylinders. At 30-50k miles, the oil control rings start to seize and consumption goes up to 1-2qts per 1000 miles. GM has a dealer-performed service involving a solvent, etc to attempt to rectify.

These are just 2 examples from my own research. Neither of the above happens on engines using 100% synth oils. In both cases the engine is fine, excellent compression, no visible wear.

Over time, the impurities in dino oil will sludge/varnish/build up enough to cause minor especially in oil control rings. Issues are exacerbated in finely-machined engines (ring grooves), forced-induction (extra heat from turbo or supercharging), or when run under particular stress (cylinder deactivation, high rpm’s, high specific output). The 100% synth does not sludge or varnish until much higher temperatures.

Another component is the additive package: 100% synths generally have very good additive packages, keeping the engine clean for a long time, and even cleaning residue left by prior dino oils.

Finally, 100% syth oil have much better viscosity characteristics: less shear thinning, less temperature thinning, little or no age thinning.

A good way to look at it is that the synthetic oil does not ‘wear out’ – the additive package does.

When my relatives/friends ask for advice I suggest 7,500 mile change intervals, Mobile1 (usually 0w40), Mobile1 filter. In reality the oil can go 10-15, maybe 20k before the additives are gone. If they are nervous, stick to 5k oil change interval. In my own cars I use Castrol “German” 0w30 or Mobile1, and Napa Gold filters.

Your Mileage May Vary :)