GeorgeH

iTrader: (2)

Luke, come to the Purple Side...

ASH8

Hey mate...

The Castrol GTX3 MODERN ENGINE (15W40) I use here in OZ says..."Extends Engine Life in Modern Technology Engines!!...WOOO HOOOOO...and,,,,and,,,
Liquid Engineering for Advanced Wear Protection (no Rubbers!) and Performance Reserve...Double WOOO HOOOOOOO!!!!!...Dang ding Dong!

On the back it says it Exceeds API SM/CF, ACEA A3/B3 requirements...

So can you please decipher for me what that means??...is it Good...is it Safe..."Dentist Leans Over to extract some Teeth" (from that Movie)...

ASH8

OH Yeah, and it says it is suitable for Petrol, Diesel, LPG and CNG Engine Vehicles...WOWWW...

And I am NO Tree Hugga...

nycgps

iTrader: (1)

sup man.

w00t ! Im SooOOOOOO gonna get like 21439018480 of those oil OMG MY ENGINE IS NOW INDESTRUCTIBLE ! YAAAaaAAA !

I love how all the company abuse the word "exceed"

with what? 0.1 ppm extra of ZDDP? that will still put them in the "exceed" category ... lol

madcows

You really should look into that specially formulated 'roo oil you guys got down under. :P

Flashwing

This is why looking at the actual formulation of these oils is important. You're going to get NO useful information on the bottle itself. Just a bunch of propaganda.

That's what motivated me to look into oils. EVERY oil manufacturer says their stuff is the best. How the hell are you supposed to know who is lying?

madcows

Throw all the different oils into a cage battle, and see who wins!

olddragger

iTrader: (3)

Diesel will hit them all with a Mac Truck!
you cant believe a dang thing manufactors tell you --exactly.
Thats why I like talking to the mechanics/part guys that have built a lot of engines and can see/hear 1st hand what was going on.
OD

ASH8

Very VERY true Mr T, BTW done my PM yet?, or shall I put up a thread???

ASH8

Yep, Watching, talking, observing, asking Q's is what I do, I have not assembled a Rotary but seen (100's) pulled apart and put back together.

My "greatest" mechanical achievement has been to replace a few head gaskets in a Datsun 1200 and my old dead Toyota (beater) XT130 Corona with a GMH "Star Fire" Australian made 4 cylinder engine...what a car, would never die, but only 1800CC OHV in a car as heavy as th 8!!..and Auto too (I am too ashamed to admit I EVER owned an AUTO...GOD I hate Automatics...sorry guys...you are LAZY!

Auto's are OK..sort of....

PhillipM

You're not the only one that hates automatics, can't beat a good sequential.

madcows

What about synthetic diesel oils from Mobil, and Amsoil?

Flashwing

Ok everyone, I apologize this is going to be a long post but I'm going to try yet again to explain my position as well as throw out a couple theories I have.

Up until now, the drum beat of my tune has been the notion that providing lubrication in the RX8, like any motor, is all about compromise. There are gives and takes in every aspect of oil selection. The problem is both complex and simple at the same time. What's complex is understanding how everything fits together. Using that understanding and applying it to the RX8 is rather simple.

As we all know, Mazda has changed their recommendation/requirement (for warranty purposes) of oil to 5w-20 from previous 20w-50 recommendations. The case has been made that the 5w-20 has been responsible for various engine failures on the RENESIS as well as advanced amounts of bearing wear. The result as been a push to use 20w-50 in your motor. I've been attempting to make the case that Mazda might have gotten their oil selection more right than wrong.

Here is what we know:
- The oil delivery system as well as the various bearings are virtually unchanged in the RENESIS compared to other rotary motors.
-The RENESIS has approx 1,500 more RPM travel than previous generation rotary engines.
-The RENESIS produces the most power N/A of any rotary engine. It produces the most wheel horsepower over other rotary engines with the exception of the 13B-REW with the twin turbo setup.

While the mechanics of the RENESIS might be similar, it's operation certainly is not. That being said, here is my point.

Prior to this, please refer to the following article:

There are a few aspects which I wanted to address.

This is one element I wanted to make sure I stood corrected on. I have not placed enough emphasis on viscosity as a major factor in film thickness. However, the statement that viscosity is NOT the only factor remains true.

I've asked what is the factor we use to determine what the best viscosity is for a motor: It could be argued that the design loads of the engine have changed and actually increased. We also know the rpm range of the engine has increased as well.

So, where does that leave us?

While I'm not taking this article as gospel, I've found the logic employed to make sense to me.

Here's my conclusion:

I do believe that a 0w-20 or 5w-20 is going to be to thin for engine operation. Looking at some of the math there is a noticeable amount of horsepower gain by switching from even a 30 weight to a 20 weight oil. Mazda clearly took advantage of this low viscosity to increase fuel efficiency and power output. I'm more than sure of that now.

However, Mazda didn't anticipate a 100,000 mile warranty and I doubt they are going to change their oil suggestions regardless of other factors.

So that leaves us with something between 0w-30 and 20w-50. This assuming all other factors being equal.

Turbo, supercharger or any other application that sees high loads should use a heavier viscosity. I would suggest a 40 weight at the minimum. As the mentioned article points out, when bearing speeds are low it tends of result in a thinner oil film. Without proper viscosity there to make up for that, a high load situation will cause the bearing to contact metal.

Every single turbo owner I know loves to jam on the throttle at 3,000 RPM's in 6th gear and overtake other cars. This is the exact situation where bearing wear could occur without enough film strength. Forced Induction platforms can see as much as 200% calculated load.

On the opposite end, if you are using your rotary for racing purposes you could actually get away with a thinner oil viscosity.

Paul mentioned previously that Mazmart doesn't see this kind of bearing wear in their race engines. He, and Rick Engman, have stated that the 20w-50 viscosity has been the reason behind this. While elements of this are true, it's my theory that the reasoning might be misplaced.

As bearing rotation increases, so does the pressure generated by that "hydrodynamic wedge" that is created. This resultant pressure actually increases the film thickness on the bearing and maintains hydrodynamic lubrication. The viscosity of the oil isn't the primary factor there, but actually it's the rotational speed and fluid physics. I believe Mazmart could easily replicate the same results using thinner oils and perhaps increase overall engine efficiency in the process.

Using thicker viscosity oils in a race application has one drawback. The greater the viscosity the greater the shearing at higher RPM's. Shearing, aside from causing viscosity loss in oils, also generates a fair amount of heat. The energy released by shearing is translated into heat in the oil. This could result in breakdown of the oil and it's additive packages. With mineral based oils, the Viscosity Index Improver tend to be the first to wear out because they are the longest and heaviest weight molecules.

In race applications, this really doesn't matter because oils are drained after every event. Thus, any breakdown doesn't effect the engine. Street driven cars, however, would suffer excessive wear if these conditions persisted for 4,000+ miles due to long change intervals.

Regardless, simply because a condition exists on a race driven rotary does not mean that the same condition can be replicated on a street driven car. The lubrication needs between the two categories are vastly different and thus using one to justify the other is the wrong way to go.

As far as I can tell, a street driven car would actually require thicker viscosity oil than one that sees only track time. Due to the longer change intervals these oils will see a greater amount of shearing and thus viscosity loss over it's life. Also, the fact that street driven cars will see higher loads at lower RPM's means viscosity plays a larger role than it does in race cars.

On the other hand, using a 20w-50 ignores the fact that since Mazda had that recommendation we have seen 3 or 4 generations of oil standards pass.

So here would be my basic guidelines:

Xw-30: This is the minimum viscosity for any RX8 regardless of use. If you tend to operate in higher rpm's (in excess of 7,000 RPMs) on a constant basis I would look into this weight as a means of preventing shearing and oil breakdown. Do not use this viscosity if you see oil temperatures in excess of 220 degrees.

Xw-40: This oil viscosity should be a minimum for any forced induction platform regardless of RPM use or operation. High loads and low RPM's mean the possibility of bearing wear on the street.

Xw-50: The only reason I can see to use this oil is if you operate with oil temperatures in excess of 230 degrees (which is dangerous), or if you are forced induction with temperatures around or above 220 degrees. Either situation I would suggest a cooling system upgrade rather than increasing your oil viscosity.

Thank you for reading. This is still a learning process for me.

madcows

Thanks for your detailed insight, flashwing.

I have also stated my thoughts on 5w20 for daily driving applications, and that it might not be providing sufficient oil flow at lower RPMs especially as combustion chamber pressures are at their highest. Couple this with roughly 40% mixture of the old, broken down **** during changes, and you have pretty low film strength.


For what it's worth, and I'm not sure how it would exactly pertain to us, but it looks like the factory recommended oil for BMW M3s and M5s is Castrol 10w60! Now, those engines spin pretty close to our speeds (in terms of rotor rotation speed, rotarys are slower), and cavitation seems to be a non issue. I know the design is different, but is it actually *that* different?

PhillipM

Cavitation isn't such an issue as they're not having to force oil through a stationary gearset for a start off, which induces air, which then increases the risk of cavitation, when you look at the sump of the M5 it is a work of art, they've got splash guards, directed flow, multiple baffles, a full crank windage plate, 4 scavenge pumps - basically, absolutely everything they can do to stop the oil getting hit by the crank and whisking air in.
The pump and internal oil lines are huge for masses of oil flow, and they run a fairly decent oil cooler setup too, and the water pump and lines shift about 4 times the coolant that the '8's does.

They're a seriously well made engine, the camshafts alone look like they've had the same machining time + cost as an entire VQ35 engine

JinDesu

iTrader: (2)

Flash,

Wouldn't synthetic's shear resistance be an important factor in this analysis? Not only does synthetics have great shear resistance, but they also recover to their nominal viscosity after being sheared - unlike dino oil.

Also, as in the other thread, I think it is extremely important to know what the oil shears to. I've heard many people say 5w30 shears to 5w20, etc, but I want to see mathematics to prove it. I tried to figure out how it works based on the cP at 150C, but I'm using on the fly math here.

ganseg

iTrader: (5)

Also, what about winter? Somewhere here I read that conventional oil base stock related to the highest viscosity of the label - ie 5W30 relates to 30W base stock. Is that going to be fine in all the temps I will face this winter? (I should get to the track twice next summer so I will be looking for the opposite advice then!)

How much damage will the two guys before my have done in the first 34K of this engine assuming they used 5W20 and redlined it regularly?

JinDesu

iTrader: (2)

If I have read correctly, only full synthetics are the 30 base. So 0W20, 0W30, 0W40 will have different start up viscosities (of increasing order).

But 5W20, 5W30, and 5W40 will have the same start up viscosities. Can someone correct me if I am wrong?

olddragger

iTrader: (3)

nice write up flash
from one of the reasons you mentioned is why we advocate and oil change before a track event and after a track event---dont forget fuel dilution can be an issue also--talking about track.
The low rpm +high load would also explain the area in which the bearings are wearing.
SYnthetics will hold their vis better but it sure gets expensive when you are doing 3-4K changes.
I am not sold on syns yet
I do think that increasing the flow will help most of these issues also. The stationary bearings are pretty wide relatively speaking to what i have seen before in recips and flow would be even more important in dealing with that issue?
Searing is another thing that deisel oil deals with better and that oil is also designed to handle increased loads that occur in a diesel engine.
again good write up--enjoyed that.
olddragger

GeorgeH

iTrader: (2)

What about HTHS viscosity? Isn't that what we should be really worried about - the viscosity of the oil when it actually passes through the bearing?

Here is the SAE chart for high temp, high shear viscosity.

Of course, the burning question is - what HTHS do we need? It is interesting that both 15w40 and 20w50 have the same minimum required HTHS, being the thickest of the bunch. 5w20, 5w30, 0w40, 5w40, and 10w40 all are very similar, with 5w20 being slightly thinner than the rest (another blow against 5w20).

Seeing this data, if somebody wants to go beyond 5w20, I'm inclined to say that they should go straight to 15w40, unless they routinely experience cold winters, - in which case use a 5w30 in the winter. I also don't see as strong a reason to go to 20w50. But like Flash said, I'm learning this stuff too and my interpretation of HTHS may be off here.

Of course, some oil manufacturers go beyond SAE specs, and that's where it gets interesting. For example, Redline 5w30 has the same HTHS as 15w40 & 20w50. And there are quite a few spec sheets out there that show oils that go well beyond SAE requirements for 15w40 or 20w50 - perhaps the right thing for forced induction?

OD, a wider bearing actually makes it easier for the film to support the bearing - more surface area = greater film strength for a given viscosity. Although, perhaps it does mean that greater pressure is required to get the requisite flow rate - that does make a certain amount of sense.

GeorgeH

iTrader: (2)

Another note about HTHS vis: I haven't been able to find any data (yet) about how HTHS changes with oil usage. I'm sure it decreases, like other viscosity measurements, but, by the same margin? Less? More? Too bad Blackstone doesn't measure this. I'd be willing to bet that abused 5w20 turns into British tea at 150 C...

Flashwing

First, your winter question. The only real concern with winter temperatures is making sure that your oil will flow. Higher viscosity oils like a 20w-50 will have problem flowing below freezing unless you use a synthetic which have better flow properties. However, there is no reason to change oils during the winter and summer months. You want the best flowing oil during startup so using your winter oil in the summer would be a great idea!

Why? Because the operational conditions of your engine will remain the same. The exception is if you encounter extreme oil temperatures during the summer months. Otherwise, if your oil temperatures remain within the 180 to 210 degree range in winter and summer then you can use the same oil. Ambient temperature doesn't effect oil when the motor is running...motor temperatures do.

I can't see any major damage caused by 5w-20 in the shorter term with mileage. Any oil is going to protect your motor. The most damage might occur with less and adequate OMP injection. Provided you're running the most current PCM flash then you should be ok.

You're almost right. Any Xw-20, 30, or 40 will have different startup viscosities. However, a 0w-20, 5w-20 will both have the same viscosity at operational temperature.


That's the problem with the numbering system. People think a 10w-30 is thicker than a 5w-30. It's true, but thicker only when the oil is cold. Otherwise they are the same.

I don't know what else to tell you Denny. Currently the only downside to synthetics is the cost.

Well, there are only two ways to increase flow. Decrease viscosity or increase pressure. I honestly believe the aspect of increasing pressure is barking up the wrong tree. You only need to provide enough pressure to keep replacing oil in the bearings. After that any pressure increases have no additional benefits.

I'll have to look into this. Thanks for everyone's comments!

madcows

Phillip, So are you suggesting that the cavitation is occurring between the stationary gear and rotor gear? I would be under the impression that a higher viscosity oil would be in order for this duty just as high viscosity gear lubes are used in gearboxes. And at any rate, we're not talking about stationary gear wear, but bearing wear. While the bearing sizes, design, and clearances are obviously very different between the rotary and the various M engines, I might have to conclude that "thick" engine oils do not pose a serious risk of cavitation in main and crank bearings, we just need to ensure that sufficient flow is available.

Flashwing said:
From what I could tell this is for the most part true. The difficult problem is determining how much flow you actually need - and how to obtain it. Stock pressure *might* be enough throughout the rev range, but it also might not be. While providing more flow (pressure is interrelated) might not aid in lubrication, it can minimize the exposure time of the oil to the very hot components in the engine, which could help prevent breaking down the oil.

I really think it's important to find out the oil pressure range in the new S2 RX-8s, as it might give us a little insight as to what mazda thinks was the issue in the S1.

PhillipM

Gear oils generally aren't as thick as you are led to believe - they're rated differently, so, for example, an 80w90 gear oil is more similar to a 10/15w30 engine oil, most gear oils don't contain detergents either - they don't need to, bar ATFs, detergents by their very nature massively increase the risk of cavitation and foaming (hence the addition of anti-foaming agents to oils).
What's interesting to note, is that even with the lower risk of cavitation from a low/no-detergent gear oil, they still use masses of anti-foaming agents to keep the film stable.

That's the problem with the rotary, what's great in one area of the engine has drawbacks in another.

madcows

So what says your about motorcycle oil besides the fact that it doesn't contain friction modifiers? (also, are the friction modifiers only for the sake of dry-start protection?)