+1

*** High-fives my 5w30 RP quart bottles ***

 

cold idle? u mean when the car first started ?

Its around 50 something degrees out. Hmm, when my car first started it always go around 520+/- 10-20 kPa (75 PSI, sometimes a bit more). Then about 5-10 seconds later it will go back down.

Same thing when I first got my Reman, 5w20. and it was around 70-80 degrees that time.

 

Ah okay, that is how mine is too. Cold idle is at about 1500+RPM's and the pressure is 60PSI or so and then as the engine warms up the pressure drops and stabilizes at around 40-50PSI at 950RPM-1000RPM fluctuating.

 

That is what I was trying to say. The area between the bearings and surfaces remain constant regardless of RPM (except for the dynamics associated with the pumping action of those surfaces). Since it's a film that provides the protection, we just need to establish a nominal flow rate to maintain the proper oil volume between the necessary surfaces. Any addition to the flow rate is just for the benefit of increased cooling/cleaning characteristics of the oil. Am I completely off?

 

The film alters thickness from the powerstroke and loads, so you need more flow at higher rpms as the loads are higher, and the higher surface speed generates more heat at the interfaces which thins the oil so that more flow is needed to maintain that thick film too, that's why all engines increase pressure with rpms, to maintain enough flow to get a relatively constant fluid film with rpms, neither of the curves is linear however.

 

Yes, it definately appears to be a multitude of small problems adding up to one big one, I'd add poor oil temperature control to that too, no fans in traffic for the oil coolers, and they're not good enough at full chat to keep the oil temperatures under control.

 

Long time lurker who just bought an R3.

Stupid question. What would be the best way to clear the used oil out of the system? Looking at Ash's figures, the amount left behind is HUGE.

 

Yeah, there is a lot of old oil left lying in rotors, e shaft and housing galleries, even if you do the "corner cooler lift" you are still only taking out about 1/3 of what is left behind.

I do a double flush...Drain, fill, start till very hot, drain, filter, fill.

 

Seems to me that running synthetic with 3-4,000 mile OCI would work to, since this is a very short OCI for synthetic, which means the leftover oil is still quite serviceable.

 

Yes, exactly. This is why using synthetic oil is critical in the RX8. Using mineral oil would require Ash's method of flushing the oil system every change which can get costly or at the very least time consuming.

Running a high quality synthetic for 4,000 miles is very do-able.

 

The curves are not linear and i will post a vid tomorrow if i remember
I'm not quite sure about the oil coolers though. Even during heavy traffic in hot summers (38°c) i never saw temperatures above 100°C.
Something to say is that now that the weather is cold (11°c) the water coolant temperature tends to fluctuate more than the oil one. After a pull today it went down to 70°c so we may add this coolants differential to the plot as well. What do you guys think? somebody might be pushing a car that is cooling "too much" in some circumstances, leading to results that are not way off of what Ash has shown in the thread opening!

 

But imagine what temperature the oil in the bearing is at if the bulk oil temperature is 100*c, with a good synthetic, you'd be fine, but most dino-oils start break down much faster above ~130*

 

another good point for diesel oil and its ability to suspend particles and maintain it viscosity.
Madcow you raise good points but remember we are thinking we are not getting enough flow currently?. Raising the pressure is the easiest way to address this.
You know it would be an idea to replace the twin coolers with one and for it to have a drain valve.
OD

 

I do want to point out one thing.

Assuming you have a static viscosity of fluid, raising the pressure will increase the flow of the liquid.

However, raising the viscosity for the sake of higher pressures will NOT yield an increase in flow assuming your pumping capacity remains static.

 

exactly ! You win Halloween candy!!
Never put heavier viscosity oil in to raise the pressure anticipating more oil flow. Ain't going to happen.
But it does usually give you better film strength so what oil that does get there offers better protection.
But the easiest way to increase flow for us is to increase the pressure--by modding the bypass's.--lol
Dizzy yet--i am.
OD

 

This is a great question. What is the temp of the oil as it flows through the bearings, compared to indicated temp? I believe the mid range viscosities flow more quickly and draw the heat off much more efficiently than the highest weight viscosities. One man's opinion.

 

oh no flash u didnt say that !

according to rxrocks over at the Synthetic oil thread. Synthetic is very evil and mazda does not "recommend" it !

 

Yes, Flash , I think you are (no you are ) right.

I do the Double Flush because the GTX-3 is about $26 AUD (5.5 Litres), where the Synth is more than twice that price.

And I like to change the filter at 5000 KMS (3000 Miles), I know it is Overkill, but, while I am still in love with my 8 I will treat her with respect and dignity, and dine at all the best (oil) restaurants...she also loves mixer drinks, so she gets the best 2 stroke (here) that money can buy (Amsoil Saber Pro)...

Got it bad ...hey!!

 

I'm actually going to probably order a case of that soon. I ordered 4 quarts and while I can't say I "felt" any difference, I do like that its synthetic and made for air cooled engines. The TCw3 or even the multi-purpose stuff kinda scares me but it's all I can find locally.

 

While on the thread Topic....

There is a member who is stripping a 12A from an RX-7 with 140K miles, while most of the engine is toast...

https://www.rx8club.com/series-i-tech-garage-22/tore-down-another-12a-185424/

He says the Stationary Gear Bearings (0820-10-502B) that is also used in the 4 port (low power) RX-8, look in excellent condition...this is an engine that used 20W50 Engine OIL at factory beginning and similar (slightly lower) Engine Oil Pressures to the RX-8...

So is it Engine OIL Viscosity, or Oil Pressure or the Extra RPM....

I know what I believe it is...

 

Here the Amsoil comes in a Carton of 10 (quart bottles)...I really like this product Flash, and it works (IMO), I also get a very clean looking Exhaust, not too black or sooty, in fact if you shine a torch up her rear pipe(s) it is a very slight Blue in color....like the Saber Pro colour.!!..

BTW, be prepared for more Bumper Soot/Carbon, which is all good.

I would rather the Carbon outside of engine than IN!!

 

I agree, I don't mind that crap getting on my bumper as much. It's already caked with pre-mix and 2-cycle anyway.

One of the best compliments I've gotten for my car was from a suspension guy who did my corner balancing. "I love your car! It smells just like a boat!"

 

If you actually live in the phoenix, you should have no problem finding motul, belray, amsoil, etc. 2-stroke at various off-road motorcycle/quads shop. They usually are more expensive than if you order it online, though.

 

Right, but in the high torque rpm range (usually at normal driving speeds), not only is the maximum pressure being applied to the oil between the bearing clearances, but since it's at a lower rpm, there is more time to allow the oil to evacuate said clearances.

Now at higher RPMs, there is more frequent "pumping" of the oil due to the higher amount of compression/combustion strokes over time. However, rotor face pressures are lower during combustion, and times are too short to evacuate much oil. With this in mind, it's hard to say (at least for me), whether it's the lower, or higher RPMs that's evacuating the most amount of oil between the e-shaft and bearings.

Now, I can't really argue that an increase in pressure (due to oil pump capacity, and not oil viscosity) would beneficially aid in cooling of the internals. But the point i'm trying to make is that the stock oil pressure is potentially enough to provide sufficient flow to keep the bearing clearances completely lubricated.

Since failures like the engine in the OP are oil related, I might just have to stick with the conclusion that broken down light weight oil (which was originally xW-30 or less) is the culprit here. Like I said before (maybe in another post?), 5W-20 *might* be ok, even though I personally would never use it, as long as you're able to change the car's full oil capacity. Any of that crap left over through an oil change is just scary.

 

There's pressure exerted from the centripetal force generated by the stroke of the rotor too, that increases at the square of the engine speed, so more rpms = massive jump in stress, and because the surface speed differential on the bearing is higher at high rpm, it slings oil out of the bearing faster from the hydrodynamic wave traveling in front of the bearing oscillation, which is also why you need more flow for higher RPMs.