So I've had this 1987 Mazda rx7 GXL for about a year now and this is the first time I've ever had trouble with the motor itself. I drove to Tampa and back with a buddy of mine and I went through about a quart of oil for the entire trip.....
this was after I did the oil change, at first I thought it was an oil leak but after taking it to Mazda they couldn't find any leaks. I tried tires plus because they were close by and they told me my engine needed to be rebuild which I feel like that's complete crap since there is no backfiring or severe power loss.
So now I'm starting to wonder what it actually is. is it because of the freeway driving? any advice is appreciated.

 

You don't mention how long the Tampa trip actually was but it doesn't really matter...Mazda's rotary is designed to burn engine oil, that's what the OMP system does.
You are always pulling oil from the sump and injecting onto the apex seals.
This is a feature, not a bug.

 

I get that it burns oil, but the amount is what concerns me.
its 36 miles from where I live to tampa, florida. so a 72 mile round trip and it went through a quart of oil.
Compared to the longest trip ive ever taken in this car (about 1k miles give or take), 72 miles should be a piece of cake.
I'm running Castrol's full synthetic high mileage 20-w50 if that has anything to do with it.

 

Ah, I see your point, that does seem excessive.
The problem is, unless you see oil on the ground or burning from the exhaust, the most logical first assumption would be that the level was low before the trip began...especially given you'd just changed it.
Absent any weird noises or behaviour, I'd top up the oil and just monitor it for a while and see what happens.
I can't think of anything proactive to do.

 

No mystery there then.
That sythetic oil has cleaned out the carbon around your oil control ring o-rings and now they leak.

I had my oil changed in my RX-8 at the same place since I bought it.
They changed ownership and I didn't realize they put synthetic engine oil in ONE TIME. Right after my next race my RX-8 started using oil like crazy.

I switched back to regular Castrol GTX I used in all my rotaries and am not changing the oil now- just adding oil. This is a terrible thing to do but running with the "dirty" oil helps add carbon deposits back around the leaking rotor oil seal o-rings in the engine. "Dirty" oil adds wear to the bearings, apex, side seals and ironically the steel part of the rotor oil seals though!

I don't like it, but it did reduce oil consumption and I am ready to change the oil to fresh Castrol GTX.

I had another rotary that smoked so bad I finally had to stop street driving it- I would race it, but start it before the sun came up. Previous owner had used Royal Purple synthetic.
I didn't think of the "dirty" oil trick back then and just sold it as junked.

 

Synthetic oil in rotary engines Is a NO NO it can dissolve the rubber oil o rings

 

Rotary Tech Tips: Synthetic Oils And The Rotary Engine

 

So if that's the case, that synthetic oil is bad for the motor, then why now did it decide to start craping out? the previous two owners of this vehicle used the same 20-w50 ive used, and this car has put over 110k miles without incident?
ive used it since I got this car and while it wasn't 100% not burning oil, I did have to add a quart or two every 1500 miles or so. Should I completely remove the synthetic blend or let it burn out and add conventional motor oil?
Edit: ok so its not full synthetic im running on, its the "Synthetic blend" motor oil which is not what I thought it was. Don't know much about oil. rip me....

 

Oh, great. Just what we needed, another oil debate.

1. Using blanket terms like "synthetic in a rotary is a no no." Is completely unnecessary here. See the racing beat tech notes.

2. The ONLY time I would avoid synthetic would be in a car with 250k miles that's over 30 years old and has never had synthetic, or in a brand new engine (synthetic is not advisable as a "break in" oil.)

3. There's no sense in running a low quality synthetic. I'd venture to guess this is probably the cause of most of the rotary/synthetic oil problems.

4. Lucas oil stabilizer WORKS; however I have never used it in a rotary with an OMP, (probably not advisable) but they also have a new thinner synthetic version if somebody wants to be a guinnea pig.

 

Rotaries burn oil, that's just the nature of our motors.

I use Idemitsu Synthetic Oil 10W-30 in my S5 13B NA and have never had any issue. When I have to top off the oil I also use Royal Purple if I am out of Idemitsu. I'll top off the oil at least 1 quart in between oil changes depending on how I've been driving. The only time I used non-synthetic oil was during the break in period of my motor.

If you're using OEM Oil Cooler Lines, check to make you don't have the smallest of leaks. Never hurts to check out the oil pan gasket and the OMP Lines (Very Fragile)

 

 

I believe it is more the additive package in the oil that matters.
Most synthetics have more of the additives that can dissolve carbon because they are meant to hold more contaminants from longer oil change intervals or extreme use which causes carbon and other contaminants.

On rotaries carbon builds up around the "rubber" o-rings in the metal oil seal rings slowly as motor oil leaks a bit due to uneven side housing expansion and burns off.
This carbon build up seals about as well as the rubber o-ring itself so the engine works fine like this.

However, if you use an oil that dissolves some of this carbon you get new major oil leaks where the dissolved carbon used to be as remaining adjacent carbon deposits keep the o-ring from sealing against the metal oil seal ring as they did on fresh oil control rings with no carbon or old oil control rings with evenly built up carbon deposits.

That is my theory any ways.

 

WELP! The plot thickens, because now its deciding to stop burning oil extremely fast and has gone back to normal...…. what the actual f**k????

 

Sweet!

My RX-8 took ~7,000 miles of "dirty" conventional oil.

 

i wouldn't worry about it, chances are that it was a measuring error or something dumb. another possibility is that the metering pump lever got stuck, and the pump was all the way on, totally possible to use that much oil in that short of a time, probably good for the engine too

 

I doubt the oil "burnt" then. If it's not leaking and there's no smoke during normal driving it was probably oil missing from the oil cooler or the oil filter after the last oil change. I've filled the pan to the "full" mark on the dipstick during an oil change and had the level go down after driving before. The oil system on these cars holds a LOT of oil (huge oil cooler) but in the grand scheme of things the pan isn't very big. One thing to note is the oil cooler has a thermostat in it. If you drained the oil when the engine was warm, It may have drained the cooler if that thermostat was open or malfunctioning. After that thermostat cools off and closes you may *think* the car is "full" of oil when you fill the pan, until the next time that thermostat opens during a long or spirited drive. (Like an "air locked" oil cooler) This is a theory... but it's probably not outside the realm of possibility.