2011 Mazda 6i - Kendall GT-1 0w20, 6,937 miles

[Eddie]

SkyActiv engine harder on oil than ?? Please give references that show data because from the data I've seen the engine is quite easy on oil. Ed

 

[FetchFar]

Originally Posted By: Eddie

SkyActiv engine harder on oil than ?? Please give references that show data because from the data I've seen the engine is quite easy on oil. Ed

Harder on oil than low-compression (average is 10:1 on cars these days) engines with port fuel injection. I'll get references.

 

[FetchFar]

Along with many experts who have cited how Direct Injection engines are tough on oil, here is one Lubrizol PCEO article about the upcoming GF-6 tests (note dexos1 is already ahead of this): http://www.pceo.com/node/262 Compared to PFI engines GDI and GDI-T engines have several unique features: 1. increased production of fine carbon particulates during combustion which can enter the crankcase via blow by and cause excessive wear 2. increased fuel dilution of crankcase lube oil (cylinder wall wetting by side-mounted direct fuel injectors allows fuel to contaminate the lube oil) 3. increased oxidation and deposits from higher operating temperatures and pressures 4. higher initial cost than PFI engines for the higher-pressure fuel injection system

 

[jrustles]

Originally Posted By: FetchFar

Originally Posted By: Eddie

SkyActiv engine harder on oil than ?? Please give references that show data because from the data I've seen the engine is quite easy on oil. Ed

Harder on oil than low-compression (average is 10:1 on cars these days) engines with port fuel injection. I'll get references.

Enh. That is only the static compression ratio, it's not like it runs combustion pressures equivalent to a cam-centered 13-14:1 all the time, the dynamic compression ratio is well within the normal range. If they show high wear and oil breakdown then I'd say they're harder on oil, but I'm not seeing it despite dilution on new engine UOAs

 

[FetchFar]

Granted I'm a little skeptical about Direct Injection DI being that much tougher on oil, yet there is a lot of evidence out there. I own a GM LLT V6 DI 3.6L Camaro, and GM changed the OLM oil life monitor on the engine computer to change the oil more often as of the 2011 model year, and recalled earlier models of this DI engine.

 

[FetchFar]

Originally Posted By: jrustles

Originally Posted By: FetchFar

[quote=Eddie]Harder on oil than low-compression (average is 10:1 on cars these days) engines with port fuel injection. I'll get references.

Enh. That is only the static compression ratio, it's not like it runs combustion pressures equivalent to a cam-centered 13-14:1 all the time, the dynamic compression ratio is well within the normal range. If they show high wear and oil breakdown then I'd say they're harder on oil, but I'm not seeing it despite dilution on new engine UOAs

They can only do so much late valve opening (emissions limited), if thats what you're referring to. Besides, the higher compression is how these Skyactiv engines get great fuel economy, so they must run high compression, the proof is right there. ... Also read the "merits" section on this web page: http://www.mazda.com/mazdaspirit/skyactiv/engine/skyactiv-g.html

 

[jrustles]

Originally Posted By: FetchFar

They can only do so much late valve opening (emissions limited), if thats what you're referring to. Besides, the higher compression is how these Skyactiv engines get great fuel economy, so they must run high compression, the proof is right there.

Well, as a design parameter, they can run as much as they want. And it is quite a bit; the reduction of pumping losses is one ingredient to the fuel economy. These engines operate in the atkinson cycle a lot of the time. The high static is for stratified lean burn combustion stability; the leaner the AF mixture, and the lower the dynamic compression ratio (cylinder charge) requires a higher static to ensure stable light off. It's for lean-burn stability, because lean mixtures tend to stumble. If the compression ratio adjustment for the NA market is confusing, consider this: it was adjusted to compensate for the octane; in which, when operating in the atkinson cycle (WOT, part load, controlled by timing retard) then the cylinder charge of say 10* retard on 92 octane will yield the same Antiknock threshold as say the cylinder charge of 15* retard (WOT, part load) on 87 octane. That's also why Mazda opted for the electronic cam phaser, because it must react as quickly as the throttle plate, as the timing retard itself is used for a good range of throttle control (with the throttle plate at WOT, variable atkinson cycle), . tl;dr the static and variable dynamic CR are balanced to offer the same antiknock performance range of the given intake phasing range.

 

[FetchFar]

These Skyactiv small engines are able to run in high torque (15% more) for sustained periods, and often do to get fuel economy. Since high torque requires, by definition, high combustion mean pressure, we can't say they aren't using their high compression capability for sustained periods.

 

[gpshumway]

Let's minimize the off-topic in the OP's thread. I'm sorry I mentioned it. Suffice it to say the UOA's I've seen of the MZR/Duratec indicate it's extremely easy on oil, so the fact that the Skyactive is harder on oil is not surprising, and I didn't intend to infer that it's an inferior engine, simply that minimizing the downsides of direct injection is not yet universal across brands. Some do it better than others and the jury is still out as to whether the new DI engines will be as trouble free as their port-injected forbears. Now back to your regularly scheduled bickering...

 

[walk23]

Could it be that Ti is a better anti wear agent than Moly ?