Nubo

We all know the rotary consumes oil because oil is injected into the combustion chamber for lubrication and sealing. A comman rate of consumption reported in the forums is 1 quart per 2000 miles. Some even lower.

I got to thinking about this and it struck me that this rate sounds insanely low.

Let's assume we're averaging 60 mph @ 3000 rpm and consuming a quart every 2000 miles. A quart works out to about 947ml. In 2000 miles that yields 0.47 ml per mile. On a per-rotor basis that is 0.24 ml per mile.

One ml is about 5 drops. So consider that just over 1 drop of oil is enough to provide lubrication and sealing for 3 apex seals and the chamber wall while enduring 3000 combustion and exhuast cycles and 1000 "revolutions" of the rotor.

This is amazing to me.

Baller

Yes....the old Wankels used twice or at certain RPM's 10 times more oil.
That is why the use of Synthetic is more than Ok.

wakeech

...ignoring where Baller's comment could take us, examine again what the oil is doing: lubricating only the apex seals.

remember how small an area this is covering, and how very little (volume-wise) you need to create a film of whatever the minimum depth is. it doesn't seem so insane to me: it's not that this engine requires less, it's simply more precise in how it's using the oil and thus doesn't require all the excess older engines did.

JCC

Some of the injected "combustion" oil gets recycled by the cut-off and side seals so not all the oil is being lost to combustion. These seals are designed to scrape condensed oil off the rotor housing side surfaces and the oil seals are directional allowing a return to the sump. One of the old RX-7 problems with real synthetic (group 4 PAO) was the rubber part of the oil seals would not swell properly and engine vacuum would suck excessive oil into the combustion and foul everything.

RX_999

Why would you ignore the Baller?
He is 100% correct.

Malcom

stickman

He probably didn't want to get into yet another thread on the use of synthetic oil. Just for the record, the suplemental booklet that Mazda hands out with the owners manual does specifically states to NOT use synthetic oil. The booklet is called Mazda Drivers Guide. It has a part number: 9999-92-rx8d2-04

RX-8 friend

If you forget for a moment that we are all rotary nuts, consider piston engines. If you build a piston engine with really efficient oil rings (too efficient), the compression rings don't last very long (I've seen some go less than 10,000 mi). If the oil rings allow enough oil by, they go a long distance. That oil is used to lubricate the compression rings, and is ultimately burned. A piston engined vehicle (take my 2001 Pathfinder 3.5 L V6 for example), uses up about one litre per 6000 km. Maybe a little more, maybe a little less.

So, one qt. per 2000 mi. is actually more than my Pathfinder uses for the same purpose. I submit it's actually more than needed. So while it sounds like it wouldn't do anything, it's actually right in there with other engine designs.

The funny part is my 2 stroke m/cs use about the same amount, even though they have much smaller displacement (ring contact area).

wakeech

two things:

1. no, it's not certain he's 100% correct. theories and heresay on the internet amount to nothing in practical application. i'm not saying he's wrong, i'm saying there's no certainty. personally, if you want to use synthetic oil, i'm sure you won't destroy your engine. will it be as good or better than mineral oil?? i don't know, neither does he, and neither do you, not for certain.

2. read carefully what i say: "ignoring where Baller's statement could take us", meaning the whole mineral vs. synthetic debate, which is where we are, which is exactly where i intended this discussion to stay out of.

so, let's keep it all on topic, and not start throwing remarks about ***** nilly.