Image for a minute that you own an '04 Miata and that it happens to have an oil sump capacity of 7.1 qts. Now imagine after a period of 2 years you present the dealer with a complaint related to an engine failure. You show the dealer your oil change receipts from Jiffy Lube for which you have records showing faithful changes every 7500 miles just like the owner's manual states. But instead of a full oil change all that was ever changed at one time was 53% of the old oil. The remaining oil was left in the crankcase. What would the dealer and/or Mazda do in this case? They would deny any warranty claims because of the improper maintenance that was performed.

Now consder the RX-8. Same claim, except that now the Jiffy Lube records show that complete oil changes were performed. What is the difference in the actual amount of oil changed?

My point here is that the Owners Manual for both cars reads the same as far as oil change requirements. Say your RX-8 is off warranty but you have a sludged up engine even after following the recommended oil change practice. Would you get help from Mazda? I don't think so.

So the conclusion here is do what RX-7 owners have learned. Change that oil more frequently. Like about every 2000 miles.

Since I have the floor let me add that the rotary engine tends to contaminate the oil with fuel. So not only does your Jiffy Lube receipt show for the Miata that you changed half the oil, but that you also had them add 0.25 qt of gasoline to the oil when it was changed. Would the dealer/Mazda be impressed with this practice?

How about the fact the the oil being diluted is 5W20. Even more impressive!

 

the other half of the oil doesnt remain in the "crank case" its in the oil coolers and the oil cooler lines.

changing the oil every 2000 miles on this car is an absurd idea.

 

Jiffy Lube likes it.

 

So far the members contributing oil analysis readings are showing the oil to be doing ok. There was an early issue with fuel dilution but the newer flashes seemed to have brought that down to acceptable levels.

 

Changing oil every 2000 miles is quite excessive. However it takes three oil changes to dilute the original oil to less that 0.1 qt. If that oil finally has 10000 miles on it, that would also be a problem if it were your standard Mazda-approved dino oil. Adding new oil to old oil does not renew the old oil. When Mazda came out with their oil change recommendations, it was the same for all their cars. Should'nt the oil change recommendation also take into consideration the specifics of a given car design?

The RX-7 owners use 10W30 oil or higher. The bearings in the Renesis engine are the same dimensions and clearances as the 13B engine. Using 5W20 oil on extended drain could be adding to the concern that I have.

 

I get my oil changed every 3,000 miles or so. As for the old oil are we all forgetting or at least in my car I am burning off about 1/4 to 1/2 quart of oil every 1,500 miles. Assuming a percentage of that oil being burnt off is the "older" oil in the oil coolers. Correct me if I am wrong.

 

Did you have a point, or did you just need to rant?

 

In my opinion, the engine oil should be changed more frequently that what is specified in the Owner's Manual.

 

Really, I would like to see Mazda approve the use of synthetic oil in our cars. It would make the extended drain characteristics of the oil change recemmendations more in line with normal maintenance procedures.

 

I had these same concerns when first looking at the car. Since then I've done a bit of reading on oil. There is plenty to suggest that the American custom of 3000 mile oil changes is wasteful and unnecessary and that 10,000 or even 20,000 mile intervals can be reasonably attained with top-quality oil. European countries typically have much longer oil-change intervals and think we're rather silly.


Not that I am going to begin disregarding the owner's manual service intervals. But I am backing away from my initial extra-frequent changes, and still feel comfortable that all is well even with the retained oil. I'm using synthetic 5w-30, so I feel comfortable about the oil's longevity and the slightly higher viscosity will help somewhat offset any mild fuel dilution that might occur. As noted, the occasional top-off due to rotary consumption does tend to speed up the retirement of "old" oil.

The true facts are obtained via used-oil analysis. Do some reading on this and about what constitutes "wearing out" of the oil. A few members have been posting their results and they're enlightening. If you're truly concerned, send in your own samples for analysis.

 

Wrong - the owners manual CLEARLY states DIFFERENT amounts for the total oil VOLUME and the oil change CAPACITY.

Check out page 10-5 of your Owners Manual - Capacities, Engine Oil (with oil filter replacement), 3.7 quarts.

There you go - for an oil change, you should only be expecting to drain and replace 3.7 quarts. BY DESIGN and by the manufacturer's intention.

So - your whole rant is misguided, misplaced, and false. WRONG!!!!

Regards,
Gordon

 

I looked at the owners manual when I bought the car and threw it down after reading the 5k mile oil change plan. I change mine out every 3k miles and at 3k it is already black.

 

Please refer to the Mazda RX-8 Shop Manual, Section 3 - Engine Specifications, Pages 31 - 32 Engine Oil Replacement:

Oil Capacity (Total Dry Engine) = 7.1 qt.

When the oil is drained for an oil change, the nominal amount of oil drained out is 3.7 qt. Approximately 3.4 qt. of oil does not drain out.

Approximately 1.0 qt. remains in each of two oil coolers. Approximately 1.4 qt remains within the engine itself. In my opinion, this oil pools inside the stationary rotors, at the bottom, in the cavity where the stationary gear meshes with the rotary gear.

 

And you know this exactly how again? News flash: guessing doesn't make it so. How can the oil pool inside the rotor housing when gravity would not permit it? The additional oil is left in the oil coolers and the oil cooler lines, not the engine itself. That's what my mechanic (a good rotary guy) told me, and it makes a lot more sense than your presumption, a presumption that appears only valid enough to suit your (weak) argument.

Bill

 

Referring to the shop manual, same section and pages:

Oil replacement: 3.5 qt
Oil and fliter replacement: 3.7 qt
Engine overhaul: 5.0 qt
Total (dry engine) high power: 7.1 qt

 

When doing an oil change is there a way of draining the leftover quarts from the oil coolers? If not, wouldn't it be a good idea to have oil cooler drain plugs? Or am I missing something here?

 

Yeah, ok. So how does this address your claim that oil is left in the engine? With an engine rebuild, oil will drain out of the oil coolers and oil lines that wouldn't drain out during a normal oil change. Duh.

Bill

 

Another controversial subtopic. The Owner's Manual states not to overfill the oil or engine damage may result. Please consider this: it is not possible for the crankshaft, etc (eshaft in the case of the Renesis) to whip the oil into a froth. The oil sits in a cavity below the rotor housing casings. The cavity is formed by the rotor housings, end covers and the oil pan.

I do not think that there is any way for the oil to get into the engine proper without being pumped through the oil pump.

My point: The issue in the Owner's Manual about not overfilling is always stated in all Car
Manuals. The Renesis may not experience engine damage if overfilled by a quart. Over filling by a quart may be a good thing if it changes the ratio of new oil to old oil. Just my opinion, of course.

Also, let's say that the oil overfill completely flooded the cavity below the rotor housings. The oil wouild then be in contact with the lower part of the rotor housings which is where combustion takes place. The rotor housings have an encapsulating water jacket so there would be significant heat transfer between the oil and the water. That may be good or bad.

 

If you can fit 3.4qts of oil in between the stationary gear and the rotor I'd love to see it!
As "EVERYONE" has stated the remaining oil is in the engine/oil cooler(s)/oil cooler lines), so get a grip.

As per your supposed warrenty claims due to oil changes, I would deny you as well. Do yourself a favour and continue to go and have the oil changed at regular intervals by a trained professional as it seems you don't really get it.
If you want the dilute the oil then have it flushed.

Also as per you fuel dilution being strickly rotary related, your wrong there to. All engines have a degree of fuel dilution.

 

Then, following that logic, why not just overfill by 6 or 7 quarts? Probably even better from the dilution aspect.

I guess the standard addage about opinions applies in full here.

 

everyone has one, some are just more wrong than others? :D

 

How about this, I will get my oil changed with the 3.7 qt every 3,000 miles or so. You can pull the oil coolers and oil lines and replace it with 7.1 qt problem solved.

 

12500 mile oil changes over here. With the amout you top up with in between most of the oil will be new anyway, It's the filter that needs changing it collects the bad bits.

 

I have read so much gibberish,

I change my oil myself, every 2000 miles, the first two changes I did at 3000 miles, so 8000 miles I started the 2000 mile interval, I am doing this as my 8 flooded twice, and AFTER the latest flash, luckily I put in an Optima Yellow Top, and this is one big dog battery,...

I use castrol oil non synthetic, and I fill it to the fill line, whether it takes 3.7 or 4 quarts, my Tundra calls for 6.5 quarts however I fill it until it shows on the stick and by that time I am putting in a full 7 quarts........

I remember about 25 years ago, my mom bought a subaru hatchback (it got 46 mpg hwy!) and my *** munch brother overfills the oil and it does not start, idiot, now he is married to some corp exec and hardly works and lives the life of luxury, guess he is not as stupid as he looks

 

Wow, lots of blasting but not a lot of good arguments.

Shocar, I think, has a reasonable thesis and I tend to agree with him on this.

It doesn't really matter where the oil is being traped. It is being retained and it is dirty.
The oil itself may be chemically useable, but it is quite well filled with particulate and gasoline.
This is obvious. Do an oil change at 2000 miles. It will be black.

I change mine at 2000 and the filter every other change. Costs me $5 and 20 minutes. Pretty cheap insurance.