GTDave

Look at it this way. If you take a shringe full of 5W20 oil at 50 degrees F and push the plunger all the way to the end in 1 second ejecting all the oil and then you take the same shringe and fill it with 15W50 oil at 50 degrees F and push the plunger all the way to the end both will have ejected exactly the same amount of oil. The difference will be in the pressure required to do that in the same time period. The shringe with the 15W50 oil will require a lot more force to accomplish the same thing. This is precisely why Mazda specifies 5W20 oil in the RX8. It gives them better fuel economy because the oil pumping takes so much less energy with 5W20 oil than with 5W30 or for that matter 15W50 like some people use. All the manufacturers have gone to a 5W20 oil for fuel economy only. If you are not interested in the beinifit to fuel economy the 5W20 gives you then change to a 5W30 or a 5W40 if you so desire. But whatever you do you will not change the amount of oil that is pumped through the oil pump on the RX8 or 99% of all vehicles.

GTDave

Give it another think and maybe you can understand how it really works. And if you can't then the laugh is on you my friend.

9krpmrx8

iTrader: (46)

You are about to get pwned.

nycgps

iTrader: (1)

*shurgs*

PeteInLongBeach

Except, your "shringe" doesn't have a pressure regulator / relief valve. Are you talking about volume of oil through the pump or through the engine journals?

Iluvrevs

Sounds like we almost saying the same thing whether we intend to or not. So, there will be a difference in volume of oil passed through the pump with varying viscosities if the pump/ecu is/are set to deliver a specified oil pressure.

These were from a quick search, check them out.
http://www.pumpschool.com/intro/selection.htm
High-viscosity liquids require considerably reduced speeds to achieve satisfactory performance. Reductions of 25% of rated speed and lower are common with high-viscosity liquids.
http://www.plantservices.com/articles/2011/07-how-to-select-the-right-positive-displacement-pump.html

• PD pump throughput is a function of viscosity, differential pressure and speed.

· Fluid characteristics play a major role with positive displacement pumps because most handle fluids other than water. The most important property is viscosity, the fluid’s resistance to a shearing force, which quantifies how easily the fluid will flow.

rotarygod

On a positive displacement pump your flow is not going to change with oil viscosity. The pressure it is at may. Keep in mind that since the engine itself is running the pump, you aren't going to be in a situation where you don't have enough power to run the pump. For a fixed power level you would decrease flow as you increase pressure. However since we don't have a fixed amount of power from an electric motor but instead engine power, we maintain flow even if pressure is different but we end up being a little more parasitic on the engine. The only potential "but" to that is if the oil is thick enough that it can't get to the pump as faster as the pump can move it.

FWIW: I designed large (up to 2200 hp) positive displacement piston mud pumps for several years.

HiFlite999

iTrader: (2)

Again, using a heavier oil will *reduce* oil flow above ~4000 rpm because the stock ~75 psi oil system pressure bypasses open sooner than with a lighter oil, especially when cold. I would not use a 40W or above without going to higher bypass pressure.

https://www.rx8club.com/showpost.php...&postcount=256

https://www.rx8club.com/showpost.php...&postcount=130

Nadrealista

bingo, that is why I was asking about oil pressures at various rpm and psi rating of our oil pressure release valve.

I have a feeling that some of the 20w-50 might never go trough the engine and is simply returned back into sump via oil pressure release valve at high rpms.

ASH8

........and the beat goes on....

9krpmrx8

iTrader: (46)

Bow chicka wow wow.

rotarygod

Yup I wasn't accounting for a pressure regulator bypass. Fortunately after the engine is warmed up any viscosity differences between any weight oils used are so little compared to each other that it's nearly a moot point.

WTBRotary!

iTrader: (6)

Yeah I installed Mazmart's Oil Pressure increase regulator... cant hurt really...

GTDave

Just for your information. When a filter bypass is operating, the oil still goes through the engine. The oil presure regulator limits the pressure and bypasses to the sump at a preset maximum during operation but will only be operating when the oil is cold. But you people can believe whatever you want. I see that some truths will only be met with scepticism so I won't bother trying in this topic any longer. Good luck with that thick unfiltered bypassed oil going into your engine.

HiFlite999

iTrader: (2)

True.

True.

Most assuredly, not true with the stock system. Watch your warm oil pressure rise with rpm. It will max out at ~70 psi around 4-5k rpm. From ~4.5k to 9k rpm the system bypasses are open; the flow at 9k will be the same as it was as 4.5k.

With the pressure bypass mod, from that 4.5k to 9k rpm, the pressure will continue to increase to ~120 psi. The flow at 9k won't be exactly double that at 4.5k, but it'll be close.

HiFlite999

iTrader: (2)

Not according to my experiments, though I don't have the numbers in front of me. Switching from 10W-40 to 5W-20 delayed the point of reaching 70 psi by about 1000-1500 rpm, while warm. It's an easy enough experiment to do on one's own for confirmation, but otherwise, why would Mazda have bothered with the 5w-20 recomendation? The lower o.p. of the lighter oil at a given rpm means a little less drag on the pump and hence better mpgs.

GTDave

I was only refering to the oil filter bypass not the oil pump bypass. You need to have fully filtered oil in an engine to make it last a long time. I don't know if 120 lbs sq" is a safe pressure. It is possible to blow apart the oil filter at those pressures. Ford had a recall not too long ago because of high oil pressures blowing the filters apart.

nycgps

iTrader: (1)

why 5w30 everywhere else ?

why 5w20? cuz Mazda (MNAO?) is retarded. well, EPA requirements are retarded.

why they set it at the current level of oil pressure ? maybe because they "thought" most people will spend most of their time below certain RPM range? just like the water pump design, its pretty much useless after 6K rpm.

nycgps

iTrader: (1)

Mazda has been using the same oil filter for decades, even for FD, EXCEPT the S2 RX-8.

it never cause any problems in FD and their "stock" pressure is something like 110 psi.

HiFlite999

iTrader: (2)

It's rather clear that Mazda isn't perfect, but interesting to note that they use 5W-20 in most all of their non-turbo piston engines.

HiFlite999

iTrader: (2)

Which is another reason I use the Series II filters since it runs with the high pressures. Summed over all manufacturers, there has been a recall on every major and most minor parts of vehicles. Does one then infer that each and every part on any one car may break because it broke on another different model car?

redline86

iTrader: (7)

An interesting note about 5w20, my wifes new durango rt with the hemi recommends 5w20 or 0w20 for max fuel economy. Think about when the car was first being released in 2003, gas prices were not as high as they are now, but that is when gas prices starting jumping. MPG's where becoming more and more important to the American consumer. Mazda already had to down grade the HP ratings due to emissions. I think they where concerned that bad MPGs of the rotary would make sales harder. My wifes hemi almost gets the same gas mileage as I do.

In my mind oil is all about heat transfer and not breaking down under that heat. Lubrication is also important but since I run a sohn I am not concerned with how my regular oil burns. 5w30 is probably acceptable for most parts of the globe but like me and 9k when you live closer to the equator where it gets hot and here in Florida we have 9 months of summer, 2 months of spring, and a month of oh I might need a light jacket then the thicker weight defiantly holds up to the heat better. 0w's are superior in MOP. If you believe in w30 then run ow30, you get all the benefits of a light oil that flows well and under heat holds up just as well. That's why I swear by my 0w40's and when the dealer oil changes in my wifes car is up, I'll be switching to that in our hemi as well. Gas mileage isn't my top concern, engine longevity is in both of my cars especially since the hemi will be pulling trailers.

9krpmrx8

iTrader: (46)

^ Yep, 0W40 FTW.

Flashwing

The RENESIS is not known for bearing failure as a popular cause of engine destruction. Combustion chamber lubrication issues, excessive seal wear or seal failure dominate the causes for engine rebuilds. IMO, a sohn adapter with clean 2-stroke oil and an OMP with increased output will go much farther to keeping your engine running than buying expensive engine oil.

9krpmrx8

iTrader: (46)

I agree, my bearings looked great when Pineapple pulled part my engine. But spending money on oil is not something I worry about, it's peanuts in the scheme of things.