Hey guys,

I'm totally an auto noob, so please pardon my question.

Been driving rx8 for 6 mth now, and pretty much every 2000 miles or so I have to fill up 1/2 qrt of oil.

Everytime I tell my friends about this, they always ask the same question: where does the oil go? Does the oil get burnt up?

Since piston engine cars usually do 'oil change', not keep adding oil every a few thousands miles.

thanks guys

 

Oil gets used differently in a rotary engine than a piston engine. By design the rotary "BURNS" oil.

 

Or to put it another way, in a piston engine the crankcase oil is splashed on the cylinder walls, thus lubricating them. Some of this oil is burned (the part that makes it by the rings to lubricate the first compression ring).

In a rotary, the equivalent surface to the cylinder wall, the rotor housing, is separated from the oil pan area. So, to lubricate the rotor housing oil must be injected into the intake stream. All of this oil is burned (in theory, anyway - some makes it out the exhaust to create "smoot" on the back of the car).

BTW, a piston engine uses about 1/2 the oil of the rotary. e.g. My Pathfinder uses about 1 L every 6000 km (there is one litre less drained out than I put back in during an oil change). My 3rd gen is the same, but about 1/2 L of the drained oil is fuel. Older piston engines used more oil.

So my conclusion is the rotary engine doesn't use a lot of oil, contrary to what some would have you believe, just a bit more than modern piston engines.

 

The oil is used by the design of the engine. Since the Rotary is so unlike the Piston engine where as the oil lubricates the crankshaft area and thw walls of the cylinder as the pistons go up for compression and expansion after combustion, the rotary has to use oil injectors to place oil inside of the rorary chamber for lubrication. This oil is burnt with the combustion of the fuel/air mixture as it is swept by the various rotar seals into the combustion chamber area of the engine. This is where the oil goes, it gives it's life so that your rotars can be lubricated too. If you want to see a sign that this has happened, got look at your muffler tips and see the soot that this process causes us. So, this explanation is from one layman and I know it to another layman. If one of the techies want to go further than that, be my guest. :D

 

My understanding is that the oil is necessary to maintain the compression seal between the apex seals and the rotor housing. Having the oil burned as part of the intake charge wouldn't be helpful in this regard. As far as I can tell the goal is getting oil, in its liquid state, onto the rotor housing. Since this area is constantly swept by the apex seals, some oil will be swept into the exhaust stream. I suspect the remainder will be volatilized by the heat of the combustion chamber.

 

I was explaining this "rotary engine uses oil" concept to my friend the other day, and he asked a question that I didn't know the answer to.

"How can it burn oil without creating an unacceptable level of hydrocarbon pollution?"

Anybody know the answer?

 

10,000 mi/gal of oil.
15 mi/gal of gas.

There is not much oil being burned, the products are sooty (so they make more grime than pollution), and all cars burn oil at some rate, even piston engines.
--Dave.

 

I had to add just about as much oil, maybe even more, to my '92 3000GT NA between changes than my RX-8. The 3000GT owners manual acknowledges this and recommends checking the oil level often and adding oil as necessary. I don't see why some people, even the car mags, make a big deal about adding some oil every 1000 miles or so. Is it that big of a hassle?

 

so you guys are saying that i don't have to get my oil changed at a dealership and i can do it myself? all this time, i thought u had to dump the old oil and replace it w/ new oil.. and dealership said oil change was gonna be around $40.. shewww

 

I've had my RX for almost a year and have 12,000 miles, I've never had to add a drop of oil...

 

$40 is way too expensive...my dealer only charges me $23 and I get coupons all the time from Mazda dealerships in my area for $18....

 

If you get very frequent oil changes you will probably not have to add oil (as the oil "change" will add more oil). But as a general rule, its good to check the level every 1000 miles. I've added oil twice over about 5000 miles.