2ZZ-GE

2k miles is a conservative oil change interval for the street...3k and above (far above) is increasingly popular

so I guess you change your oil ever 1k or less....that's NUTS imo...I'm referring to street driving here

dgeesaman

iTrader: (7)

Waiting 3k or more is increasingly foolish. 1k is overkill for street driving, 2k is a nice conservative number.

3k max. There are turbo bearing to take care of and fuel dilution working on the oil as it gets older.

Dave

a3dcadman

iTrader: (1)

My last oil change I tried Mobil One extended performance 5w30, and last nite I also put in 5w30. I run 2000 - 3000 miles between changes depending on how I drive during that period and weather conditions. I dont track my car but get on it hard a few times every time I drive it if feasible. Was using 15w50 for years in all my vehicles.

The reason I decided to try the 5w30 was an article I read done by a college professor discussing oil ratings, viscosities, the various components in oil etc. He emphasized quite a few times how almost all engine wear occured at engine startup. Using a 5w__ oil was the best way to reduce engine wear.

chuck

DamonB

Changing the oil in an FD every 3000 is already a very conservative number. Any more often is just a waste of money IMO. On a "normal" car I do it every 5000 and have absolutely no worries.

DamonB

Only partially true. You must remember he was talking about startup so the correct phrase in your statement would be "Using a 5w__ oil was the best way to reduce engine wear at startup.

As the oil is highly stressed and gets hot the viscosity will be too low. Hence the reason hot, hard running engines often use heavier weight oil. You can certainly prove an engine makes more power with thinner oil (duh), but it often does that at the expense of life.

a3dcadman

iTrader: (1)

You must have read the same article. At startup is correct. What I have noticed is that the engine does have smoother starts and the engine seems to rev a little faster. My oil pressure still goes up to almost 120lbs and at idle is 30 - 40lbs. On the change last night the oil was dirty and definitely thinner than when I put it in, but it showed these same characteristics with the 15w50 changed at the same intervals under the same driving conditions.

chuck

edmcguirk

So what did they change in the Rx8 engine that allowed Mazda to spec 0W20 oil?

DamonB

I'm talking out my *** and don't know on the RX-8 engine but usually the oil weight is directly related to bearing tolerances and material.

Julian

iTrader: (14)

And EPA figures, Biggest driving force for car companies is reduce friction to improve EPA numbers, hell with engine life after to warranty

Kento

Bingo. It's also the driving force behind the latest API oil standards, where fuel economy numbers are everything, leading to loads of friction modifier additives and thinner viscosity oils.

turbojeff

iTrader: (30)

To throw my .02 in here.

TIIs run thicker oil at a lower pressure. At the least Mazda raised the oil pressure in the FD, maybe in an attempt (sucessful or not) to make the lower viscosity oil work as well as the higher viscosity oil. I don't know if the bearing material and/or tolerances are different.

That said I don't think they were counting on 10% fuel in the oil either. I ran 20W-50 in my FD and when I had it tested at Southwest Spectro Chemical it also had low viscosity (no brainer) for the weight listed (20W-50).

Mazda may have changed oil pressure again to run thinner oil in the RX8.

My friends had a 92 Accord with 200K miles on it, ran great and used 10W-30 it's entire life.

edmcguirk

I think after 10 years Mazda might have noticed oil dilution, after 20 years they should know if it matters. Perhaps at 10% fuel in the oil, it reaches an equilibrium as it evaporates out of the oil. Perhaps the modern oil additives can handle it.

Apparently Mazda believes that the engine will have acceptable longevity on 0W20. After all 0W20 didn't really exist before synthetic oil.

Oil pressure is set by bearing clearances only up until the RPM where the oil pressure relief spring opens up. Perhaps the Rx8 has a higher volume oil pump to maintain pressure with a lower viscosity? Or perhaps it was entirely a paperwork change?

I am already experimenting with 0W20 in my piston engine and I am considering putting it in my Rx7 racecar. I have a friend who is pit crew for a front running Star Mazda team. Maybe he can tell me what they use.

I don't know the answers but I have read some pretty convincing articles that claim lower viscosity is better. As long as pressure is maintained. As long as metal to metal never happens. Thinner oil will flow faster thus carrying more heat away from the engine. Above 200 degrees the differences in viscosity are not really huge. At low temperatures the difference in viscosity IS huge. Below room temperatures even 0W oil is too thick.

I hear that race teams that rebuild engines every race are using thinner oils but they are not seeing increased engine damage. It's a real risk. Modern oils may have flipped accepted wisdom on it's head. I don't know the answers but I am keeping an open mind.

ed

DaveW

Correct!

Improved machining techniques and closer tolerances are allowing running thinner oil, with the resultant benefits of less wear on startup, more power, and better fuel economy.

Kento

0W oils have obvious advantages, but they have some definite disadvantages as well. While they definitely offer less parasitic losses due to viscous drag, their viscosity degradation curve is much steeper than thicker oils, especially when subjected to any shearing forces such as gear meshing, etc. Is it significant enough to affect long term usage? Apparently not if Mazda feels confident enough to recommend them. Although I would have to believe that the 0W oil Mazda recommends must have a significant amount of long-chain polymers to keep the oil's viscosity from going to hell if exposed to extremely hard use and high temps.

dgeesaman

iTrader: (7)

I'll bet there is any fuel economy or emissions performance to be gained by the thinner oils, many manufacturers will trade off the extra wear and higher tolerance requirements. It's my understanding that it is that difficult to meet US emissions standards without raising cost.

Dave

edmcguirk

I don't know about viscosity degradation. All the tests that I have read say that oil gets thicker as it ages.

Oil does not break down, it's additives get used up and it gets dirty.

ed

Kento

The EPA fuel economy standards are also difficult to deal with for the manufacturers. The US government basically mandates certain fuel economy standards for various vehicles; they are subjected to a very strict test regimen, and if the particular standard isn't met, the manufacturer has to pay a stiff tax penalty.
Uh, no offense, but you haven't read very many tests then. Sorry, but oil does break down after use; if it didn't, there wouldn't be the need for some of additives put into a motor oil. There are literally hundreds of standardized lab tests to determine an oil's ability to maintain viscosity. One is called the "TB-20" or "Tapered Roller Bearing Test" (standard designation CEC L-45-99) where a tapered roller bearing spins submerged n 40ml of oil at 140 degrees F at a constant speed for 20 hours. All oils suffer viscosity degradation; I've seen SAE 40 degrade to 30 and even 20 after this test.

edmcguirk

There's lots of stuff I don't know about oil and I would be happy to learn more but the tests I have seen in automobile engines show the viscosity increasing with time and the additives are primarily described by their anti-corrosion properties.

I wouldn't argue that oil can't be broken down but in an automobile engine it does not appear to be among the important factors especially with modern synthetic oil.

Does thicker oil have higher limits -> yes. But once you prevent metal to metal contact, there doesn't appear to me to be a huge benefit to increasing viscosity. While there does appear to me to be a benefit to carrying away more heat, causing less pumping loss, and supplying quicker cold temperature lubrication.

My question is, "Is 0W20 synthetic oil good enough to protect an engine even under severe use?" The information I have seen so far, implies that the answer does not have to be "no".

ed

Julian

iTrader: (14)

Dino oil does break down, because the VI enhancers added to thicken it get sheared (molecule strings cut into pieces). Full syn oils have more stable VI over temp range and usage. That is why a syn flows at -40, cause it did not need beefing up with VI enhancer to stay viscous at op. temps

edmcguirk

In my mind the real problem is that piston engines have different friction modes than rotary engines. Most of the oil in a piston engine is working in bearings like the main bearing, rod ends, cam bearings, etc. The rotary engine's eccentric shaft seems to me to experience different kinds of sliding rotation along with the stationary gear.

We have to wait for someone to try it out and at some later date tell us what he saw during a rebuild.

I would like someone to prove me right or wrong because otherwise I'm probably going to put 0W20 in my racecar and run a 4 hour enduro at Summit Point. (I'll probably test it out at a sprint race at Watkins Glen before that.)

ed

Kento

Um..."viscosity increasing with time"?? I'd like to see these tests.
Plus there's pressure additives, friction modifiers, flow enhancers, etc., etc. TBN additives are part but not all of the additive package in most motor oils.
It is important, otherwise many of the additives wouldn't be necessary.
If that was the case, then the manufacturers would all be running 0W0 oils by now. Viscosity is necessary to keep an oil film on moving parts where there is no oil pressure.
It depends on what engine it is used with, and for how long. That was my question.

edmcguirk

Look in the Past Results area for Mobil1 and Amsoil
http://neptune.spacebears.com/cars/s.../oil-life.html

In this synthetic oil life study both Mobil1 and Amsoil increased viscosity over time. Amsoil actually moved up from a 30 to a 40 weight oil.

I have seen this mentioned in other web pages but I can't find the links right now.

ed

edmcguirk

I have seen on TV I think it was a Nascar team mentioning that they are using 0 weight oils in qualifying. And that while they are not claiming to use 0 weight oil in the race, they are not seeing any dramatic wear due to the oil.

ed

DaveW

There are (at least) 2 conflicting events happening during oil's life in an engine:

1) Molecules are being severed by shear forces, decreasing viscosity, and
2) Molecules are being polymerized (cured together) by the presence of acids (products of combustion) and other catalyzing substances (viscosity increase).

Perhaps some people may be old enough to remember 30 or so years ago when some Quaker State (non-synthetic) oils polymerized to the point that they actually solidified to a gummy mess after extended use at high temperatures and ruined engines, and needed to be scraped out of oil pans with putty knives, etc.

Kento

Correctomundo. It should also be noted that the catalyzing of many of the insoluables by heat over extended periods is giving a somewhat "false" centistokes reading. I've seen that site before. The problem with simply using oil sample analysis to determine an oil's effectiveness inside an engine is that it's like viewing the world through a pinhole; you're not even close to seeing the whole picture.

This is what I meant by what type of engine you're using the oil in. The majority of the engines used in those samples are very understressed designs. Meanwhile, our rotaries are exposing the oil to very high temps (as well as moderate fuel dilution) as well as shearing action within the stationary gear.