ASH8

Just got back from a face to face talk with my Mazda Dealers Service Head Tech, I sent him the pics of the Internal UK RENESIS Engine Damage/Wear for comment yesterday.

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Simply put there are two reasons why the back bearing is wearing the way it is and that is "Oil Pressure" and to a lesser extent oil viscosity.

The RENESIS 1 has the same Oil Pressure... Oil Pump Rotors, Oil By Pass Valve and Eccentric Bearings as Mazda's last NA Rotary, the 13B FC RX-7.

Back when this model was around the recommendation for engine oil was 15W40 (here).
Because of this higher Viscosity Oil, Oil Pressure and Bearing Wear was not an issue like we see at the moment in some S1 RX-8's.

When the RENESIS RX-8 came out the recommendation (because of Fuel MPG and Emission targets) was a 5W20 or 30.
While there is nothing wrong with these oils, what was occurring over oil use/age was a lower engine oil pressure value
therefore not enough oil getting to the Rear Stationary Gear Bearing for lubrication....particularly at start ups.

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In the Series II (09~) Oil Pressure was almost doubled, but the same oil grade recommended??

I asked why the large increase in Oil Pressure Values.
60% is there to supply the two new EMOP's Lubrication System for the Apex Seals, with the other 40% for engine oil supply,
particularly all the Rotor and Stationary Gear Bearings and improved oil flow through oil coolers.

He believes the 5W20-30 weight oils for the S2's are fine because of the engines higher oil pressure.

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So, my next question was what can RENNY 1 owners do about the oil pressure, (unofficially official)

.....to use a higher viscosity grade of engine oil which will help increase the engines oil pressure at the "critical" locations.

In other words a higher oil viscosity will equate to Oil Pressure values like the NA 13B RX-7 which has the same oil pump and related parts and values as the S1 RX-8.

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I also asked him about the use of Magnets on Oil filers and or sump drain plugs...his word was DO IT....it is all good.

Then what to do about middle Apex Seal wear, and we know the "unofficial" answer to that one, and it goes in your gas tank...

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So, there you have it, I know it is not all Groundbreaking or Revolutionary news, I thought it deserved it's own thread.

What was interesting to hear is the lower oil pressure because of the lighter (thinner) weight oils, which is what some members discussed.

RG also mentioned the Bearing Wear was due to a lack of engine oil getting there.

PLEASE No Cussin....

05rex8

iTrader: (7)

I use RP 0w40 and Idemitsu premix. I should be ok with that I think.

9krpmrx8

iTrader: (46)

So........Viscosity huh.

ASH8

Yep, I am not that keen on 0W oils but RP is a good product, so is Idemitsu...u are fine.

I forgot to add the issues can also be a too long a period in engine oil changes, low level of engine oil and no baffles in the sump pan, which are being installed on the re-man engines in the US.

ASH8

I know it can be boring, but I was really interested to hear what he had to say.
And a lot of it makes sense, Mazda really stuffed up on two things..

Oil Pressure and Oil Metering.

rotarygod

Oil pressure actually goes up as viscosity goes up. Greater pressure could come from a different pressure regulator. Of course this only regulates max pressure which is really only at higher rpms. What are the oil pressure values for each engine at 3000 rpm? That should show if there is a difference in pump or if it is merely a regulator change.

If the RX-8 uses the same oil pump as the last n/a RX-7, then the TII oil pump should be a direct swap. I know it fits as I've bolted one to the Renesis test housing that I have.

9krpmrx8

iTrader: (46)

Hey man its not boring at all. I wish Mazda would have told us all this instead of keeping us in the blind. I read a lot and did my own freezer test and I just could'nt see using a heavier weight oil.


I only wish I had a chance to take apart my engines to inspect the damage myself.

9krpmrx8

iTrader: (46)

Sorry for my rotary ignorance but can I ask what you are getting at RG?

ASH8

Yep that is what he said and have said....RG

rotarygod

I actually edited my response twice while you guys were responding.

9krpmrx8

iTrader: (46)

I see that. Thanks.

ASh, do you have oil pressure data at 3,000RPM?

ASH8

The S1 RX-8 oil pump rotors, shaft and drive chain are the same as an NA FC
Mazda Part number N326-14-140, N326-14-151. there is No IF there RG.

The By Pass Regulator Pressure Valve is also the same #3648-14-250 on rear iron housing.

This 3648 regulator is not on the Series II's, that has been taken over by the New Oil Pump, in other words the Oil Pump has the by pass valve built in.

Series II RX-8 uses the same Oil Pump chain but there are no serviceable parts available for pump itself , only as an assembly N3R1-14-100A.

9krpmrx8

iTrader: (46)

So what would the TII pump get us series 1 guys?

ASH8

Reference value PSI....50.8 @3000 RPM Series 1 RX-8, 72.5 @ 3000 RPM Series II RX-8..at 100c

If the NA RX-7 has the same Oil Pump, chain, rotors and Oil Pressure By Pass Valve then the values have to be the same, give or take a few PSI....

The RX-8's Opening Pressure regulator for the Oil Pumps..

S1..64-71 PSI
S2..156.6 PSI

RX-8's Oil Filter By Pass Open..

S1..11.4-17.1 PSI
S2..20.3-26.1 PSI

rotarygod

I'll try to quickly explain the pressure vs viscosity relationship. I work in design and engineering large mud pumps (up to 2200HP) for oil drilling. Our pumps are piston style good up to 7500 psi but we can do plunger style to 15000 psi if necessary. Our pumps are positive displacement style as opposed to a centrifugal style which just can't build the needed pressure. The oil pumps on our rotary engines are positive displacement using what are basically rotors such as a roots blower. Nothing more complex that than. However they don't compress. They just move. That's why they are displacement pumps. They displace. In order to compress, you have to choke off the outlet.

This raises the pressure. However it doesn't do it for free. In order to increase the pressure, we need to decrease the total flow. For a simple example, go play with your garden hose. Take the nozzle off and you have lots of flow but little pressure. It doesn't spray very far. There is no restriction. Now install a nozzle. It is always a restriction. When you open the nozzle all the way, it sprays far. It is a restriction over no nozzle which raises the pressure and causes the water to spray farther. Take 2 empty buckets. Fill one completely with the hose on full but without the nozzle. Time it to see how long it takes. Now fill the other one with the nozzle on and open all the way when it sprays hardest. How long does it take? If they fill at the same rate, there was enough power available in the form of water pressure to maintain flow at the nozzle pressure. Max flow will actually be without the nozzle but this is the least pressure.

On our pumps at work, we can change the piston and liner size. As built the pistons are 6" diameter. We can go down to a 4" on the small size or a 8" on the large size. If we want to run higher pressures, we use smaller pistons and liners. Stroke stays the same. You can probably tell that flow will decrease with smaller pistons as it's the same as reducing the displacement. However if we maintain the same amount of horsepower into the pump, we increase our leverage on our working fluid and we can compress it more.

Here's another test to demonstrate how this works. Let's use Coke cans. We need 2 of them, empty. Put 2 of them on the ground side by side. You can see that you have the top area of 2 cans. Now see if you can stand on them. If you are careful, you can unless you are really heavy! Your weight and the pull of gravity represent a force that is being applied to it. Obviously if you jump on it you can crush them but this is just an example. The area of both of those cans represents a larger piston as we can just pretend it is 1 object. Now lets take those 2 cans and stack one on top of the other. Now assuming you can stand on them without falling off and breaking a leg, you'll notice really quickly that they crush. They same total area was there and the input force was no different. However we increased our leverage and from a can standpoint there was twice the pressure being exerted on them.

Now this assumes we have the same input horsepower. However the chain driven oil pumps on the cars have practically an endless amount of power. If the pump speed is not changed, but the viscosity of the oil is changed, that means the amount of power to move it must also have changed. If we use a thicker oil, the pump having it's speed maintained must have more power being put into it in order to move this oil. That means more power robbed from the engine which is why oil weight is a modern issue.

Now lets take this one step farther. Let's go back to our hose. We know how far water can spray with the nozzle at full blast. How far do you think maple syrup would spray if the pressure were the same? Of course it wouldn't go as far. It would have more pressure but less flow. In order to match the flow level, we'd have to raise the pressure. The only way to do that is to increase the input horsepower. Remember how we just said the pump uses engine power? An interesting side effect of using a thicker oil is that no more of it gets to any parts of the engine and perhaps less of it does. If you aren't completely confused by now then consider yourself lucky. There's actually much more to it but I'll spare you any more for now.

Just as an fyi and I'm sure this will add to the oil debate, in my 1990 n/a RX-7, I run 5W20 synthetic oil.

rotarygod

156.6 psi. Holy freaking crap batman!!!! Wow!

Judging by the info, it's probably safe to say that the S2 uses a larger oil pump which means more pump displacement per what may as well be the same amount of oil passages. That means more pressure.

9krpmrx8

iTrader: (46)

Wow, great info as usual RG. So if in my S1 I'm getting around 65-70psi at 3,000RPMS its due to the 0W-30 I'm using?

I will double check my PSI at 3,000RPMS first thing tomorrow to be sure.

ASH8

1080 Kpa (S2) to 441-490 Kpa (S1)

What do you think would have to be done to put the Later oil pump on a RENNY 1, apart from the obvious, and could it be done.

ASH8

Don't forget at 100C or a HOT Engine.., for what it is worth your figures ^^ 65-70 psi are what the factory says it should be, but is it enough PSI??

9krpmrx8

iTrader: (46)

Yes definitely on a hot engine. Oh okay so what does the reference value of 50.8 PSI@3000RPM mean? Sorry for the confusion.


Edit: Woot! 4,000 posts.

rotarygod

If the front housings aren't different then I'm sure the changes would just be the obvious ones such as front housing, pump, etc.

Incidentally we'll probably never see the oil system go completely electric due to the variance in viscosities among oils. The omp in reality flows so little that it's not much of an issue. If we ran an electric oil pump, the electric motor would only have so much power. Unlike the chain driven, we don't have all the power of the engine available to do the work. If we had a full electric oil pump, then as oil pressure went up, flow would definitely go down. As it stands with the current mechanical pumps it doesn't. Pressure just goes up but so does parasitic loss on the engine.

While we think in terms of numbers, and even looking in viscosity in cSt may look daunting between oils, the reality is that a 5W20 and a 20W50 aren't very different in warm temperatures. When the engine is fully warmed up and the oil is hot, the difference in viscosity between a 5W20 and a 20W50 is only about 8-10 cSt (centistokes). That same 5W20 oil at even 100*F will be several TIMES thicker in terms of cSt number. What I'm getting at is that the difference is so small when warm that I doubt you'll see anything different on a gauge when the engine is fully warmed up.

9krpmrx8

iTrader: (46)

True. But what is your opinion on cold starts (let's talk Texas temps)? How much damage do you think is being done there? Some say very little but in reality I haven't found any real data (if there is a way to determine this).

RIWWP

iTrader: (2)

I got Ash's opening post, and got confused by RG's explanation, but I think what you are saying RG, is that we could increase the pressure by using a thicker oil, but that doesn't mean that the increased pressure will actually be effective, and that it is better to increase pressure mechanically with a thinner oil than to use a thicker to increase pressure through fluid dynamics?



Sorry, trying to understand the points

alnielsen

iTrader: (4)

OK, let's say you increase the viscosity of the oil you are using. The pressure goes up, but you decrease the flow. Hopefully, the only thing the oil has to carry away is heat. Doesn't the increase in viscosity allow you to run higher oil temps?

rotarygod

Bearings don't need oil pressure to be lubricated. They merely need oil flow to them. They need oil film strength to survive and it is falsely believed by many to be based purely on oil weight. It is really a formulation issue. Weight is a part of it though.

When we increase oil pressure in our engines, the goal is to get more flow. We can't get more flow without using more horsepower unless we use a thinner oil. Keep in mind what is technically true on paper doesn't mean that in the real world it's enough to matter. We want high oil flow only because we are trying to cool our rotors. Only the oil does that and the faster we can get oil in and our of the hollow rotors, the faster we can get heat out. The better we can control rotor temperatures, the better we can control emissions and power since reduced hot spots on the rotor faces means less liklihood for preignition or detonation. There is more to the oil system change than just the apex seals although that is definitely a big part of it.