RotaryLife99

Hello All,

I am new to the RX-8 scene and this is my first RX-8, so pardon my lack of terminology, but I'll do my best to illustrate the point of this thread with my current knowledge of rotary engines from surfing these forums.

I recently purchased an '04 six speed manual transmission RX-8 with 101k miles. I knew there was a risk that the engine could have low compression when I was researching common issues with these cars on the forums. I also learned that premixing is life. I started premixing with every tank of fuel since day one with .5oz/gallon of fuel. I am using Idemitsu Premix Rotary Fuel Lube, for reference purposes.

I have put about 2k miles on it in the past 3 months of owning it and it has been the most fun you can legally have in a car. The engine has shown no signs of low compression from the symptoms described on here, but I had two recalls for the driver and passenger side air bags, so I took the car in for work. While it was at Mazda I decided to have a compression test done, just to see what condition the engine was in. I was informed that my compression was very low and a new engine would be needed. I was also told that the premixing might be keeping this engine alive with no symptoms.

I started thinking through my options and weighing them out when I had an interesting idea. Since the engine is showing zero signs (knock on wood) of low compression with the premixing, I thought it would be fun to see how long it would last (while I save up for a rebuild) and document the symptoms of low compression/engine failure while premixing a low compression engine, if and when they start occurring.

I will update the thread periodically with a mileage reading and the symptoms that are present. Throughout this process I am reaching out to you, forum users, with possible tips and tricks to stretch the longevity of this engine and possibly stories of your low compression engines.

Any feedback will be appreciated.

Currently at 103,700 miles and counting.

-RotaryLife99

Reoze

Something to keep in mind. The longer you run the engine in the state that it is in, the more expensive your rebuild is going to end up costing. What were the actual compression numbers?

RotaryLife99

I realize that this is unfortunately what will result from my actions. My thoughts of getting a rebuild done is if it's in a rebuild-able state currently. According to the numbers on the forum from another user, my RX-8 is at the point where the one rotor is completely shot which might put this engine in an un-repairable condition. I'm not sure if I can get to that point, but my numbers are very low. According to the Mazda tech :

Rotor 1 is
Leading RPM: 256 with 5.6, 5.3, 5.8
Trailing RPM: 255 with 5.7, 5.5, 5.8

Rotor 2 is
Leading RPM: 265 with 6.3, 6.2, 6.2
Trailing RPM: 263 with 6.2, 6.3, 6.2.

RotaryLife99

Just to get an external source on this. I have none of these symptoms https://www.carsdirect.com/car-repai...-rotary-engine. Something is fishy about this

UnknownJinX

I am actively resisting the urge to make a "that's what she said" joke or other jokes of similar nature when I see the title.

Anyways, the low RPM during the compression test may just be a weak starter. 04 and early 05 are notorious for this, and many people choose to upgrade to the more powerful model in later years. I don't think any starter goes to 380 RPM during cranking(correct me if I am wrong). If your battery is old and weak, however, that could also be the cause.

If you don't trust the dealership, find someone else to do it, be it another Mazda dealership(hopefully with sufficient rotary knowledge), a rotary shop, or a fellow member here around you.

If your compression is really that low, the engine is not your only concern. Your cat will start to suffer from all the unburnt fuel and will eventually clog up, which greatly accelerates engine wear further. Cats are not exactly cheap, either. Even a quality mid-pipe isn't that cheap.

As for premixing, people have different opinions on it. I personally do it on my S2, with Idemitsu Premix as well. Bloody expensive(especially with the Canadian Dollar down the toilet drain these days), but a case of dozen should last a good while(simple math told me they should be last at least 10 months).

Also, check your ignition components if you haven't already. Bad ignition coils also kill engines.

RotaryLife99

I partially intended for that

I have a feeling that my battery is weak and I looked at the starter when it was up on the lift. It's the one that was original to the car. Is there a certain new type that I should be attempting to locate if I go about installing a new one.

I thought the tech knew what he was talking about because he has an RX-7 personally. He was also baffled by my engine because the he test drove it searching for "common symptoms" of low compression and noticed nothing as well.

Thanks for your feedback UnknownJinX, I realize there are tons of low compression threads on here and I have read a lot of them, so I appreciate any words of wisdom.

I'll poke around and find out the proper voltage for the battery and correct rpm speed for the starter to see if I can test if they're bad.

Thanks!

UnknownJinX

People knowledgeable about RX-7 are not necessarily RX-8 masters, although there is some common knowledge.

Just ask for a starter for a 06~08 RX-8 and you should be good. I heard S2 starters also work, don't quote me on this, though.

If you are really curious about the compression, stop premixing for a tank. Then drive the car, make sure it warms up, and shut it off. Wait for 10~15 minutes, and crank it. Does it take a long time to start the car up? Difficult hot starts are usually associated with low compression.

RotaryLife99

Perfect I will search out an 06-08 starter.

I can give that a try without the premix and see what difference it makes.

Now, theoretically speaking, how long could my engine last if I was using the pre-mix religiously? I bought a case of it when I bought the car, so I will use it as long as the engine is still firing and my catalytic converter is not glowing after each drive.

RotaryLife99

As a side note, speaking of rebuilds and such, does anyone know of a good place in NY to get a rebuild done that has a good track record?

sinkas

I am surprised it starts when hot in summer with those numbers,
When i started premixing i thought the exhust pulse dounded firmer, as though compression was higher.
Id say just keep going, but do coils plugs n leads and gut the cat

RotaryLife99

It starts perfectly, that's why I was suspicious on the test. It gets up to speed well. After it failed the compression test, I drove it 3 hours of highway driving at 78F and not even a hiccup or hesitation. I even turned it off 2/3rds of the way through the drive, checked my oil levels, topped them off and fired it right up and kept going. I'm so confused. I hate to even think this could be an option, but they had the price of a new engine ready to ship out for tomorrow to the tune of $6500, it makes me question if everything was legitimate. I laughed and said nah I'm good.

UnknownJinX

Just thought of a good point: what's the altitude of wherever you live?

I remember a thread where someone had "crappy" compression numbers, except that he stated he lives 3000 ft above the sea level. Punched those numbers at the compression number normalizer at foxed.ca, and it got better normalized compression numbers than mine. Altitude apparently can throw off the reading by quite a bit; the higher up you live, the lower compression you will have in a test.

Anyways, a case of Idemitsu should last you a good while before you need more. Idemitsu Premix also shouldn't mess around too much with the cat - I read somewhere that its base stock leaves virtually no deposit behind.

Another nice thing to have if you premix is one (or more if you want) Rotary Bum bottle and the little funnel Rotary Bum also sells. The Idemitsu Premix bottle has a pretty bad tendency to leak if you put it in the trunk. The Rotary Bum bottle does a much better job at containing the Idetmitsu Premix, and it's opaque with volume lines(oz and mL) on the side for more precise pouring.

Gut the cat only if you can confirm that it has an issue. The thing is pretty expensive, about $1300 a piece for a new OEM one.

RotaryMachineRx

iTrader: (1)

An S2 starter will work fine, there is also a thread somewhere in the tech section that talks about good aftermarket starters that are much cheaper than buying a mazda one. I have an 04 with an S2 starter on it and it made a world of difference for starting up, one blip of the key and it fires up every time. I'd be weary of those number they gave you as well, from everything you've mentioned is sure doesn't sound like you have a compression issue....

Edit: give this short thread a read: https://www.rx8club.com/series-i-tec...pgrade-213280/

RotaryLife99

The altitude is 380ft and they used one of those Mazda compression testers which spits out the three numbers on each spark plug port, so it seemed pretty legit. The numbers were not printed out, but hand written so I never personally saw the number listed on the machine.

I do have that issue, I currently have a small box that I store a small measuring cup, a funnel, and a quart of Idemitsu. I will have to look into the rotary bum bottle, sounds a lot more convenient than my oil filled box of premix items.

EDIT: Thanks for the pro tip, I just ordered 4 Rotary Bum Bottles and a funnel!

RotaryLife99

Thanks, I'll look into that. It doesn't start rough or hard, but it does seem like a weak starter. I agree that something is not adding up.

Sounds good, I appreciate the feedback!

lOOkatme

run a gallon of water through her to steam clean the engine out. then drive the living hell out of it.

Reoze

With such low but consistent (between each face) compression numbers. I would think it was an issue with worn seals over carbon buildup.

lOOkatme

I would still run a gallon of water through the engine at 3-4K rpms and then let it idle for a while. change the oil and drive the **** out of the engine for a good 1-5K miles. I mean you can drive regular in between but get it heated up and heat cycle the engine to loosen any crap in the engine. I did this with mine and it shows great compression numbers and idles well at 6-8K feet above sea level. The engine feels like it has more power as well. Another thing to think of is running a denso MAF sensor or OEM. other MAF sensors like autozone caused the car to idle erratically and sometimes would shut off during hot. the car would start right back up no problem, swapped to a Denso sensor and it idles just fine all the time now.

swap to a stronger starter as well to keep it running. Worn apex seals will show problems at hot and cold idle/start up. most people have hot start issues which typically is carboned up rotors IMO. keep cycling water through the engine and running it hard and it typically clears up. Make sure you have strong ignition.

I run mine hard a lot and I get all sorts of black carbon all over the rear of the car, on the bumper, trunk, etc. I have a gutted cat converter and stock everything else.

Chris_niday

Nice

RotaryLife99

Is there any risk with me doing this decarbonation? I have heard people doing this with seafoam and either a full can in the tank or connecting it with a vacuum hose and having it sucked straight into the motor. This can result in the gaskets and seals failing when you do this on higher mileage vehicles. Do you think this would put my engine at risk if I did this with water/seafoam or should I go for it? I want to stretch this engine as far as I can and do not want to put it at more risk by ruining seals and such.

What are your thoughts on this guys?

UnknownJinX

Seafoam doesn't do anything to seals. I don't know where that came from. My guess is that some dummies grabbed the Seafoam Deep Creep(don't run that stuff through your car).

Seafoam now also has a spray that you can spray into your intake hose. I don't know anyone here who has tried that kind. I have a can lying around(I wanted to try it on my old POS Corolla, but sold it before I had a chance to try it), and I am still debating whether or not I should use it.

lOOkatme

I ran a gallon of water through the two service ports on the side of the engine. I have 132K miles on my engine. Water is free and its the most effective way to decarb. I wouldn't waste my time with seafoam honestly.

http://www.rotaryresurrection.com/ro...injection.html

RotaryLife99

I think you have sold me on the process with water, I'll give it a try before my next oil change and see what differences it makes. One video suggested water and premix (water and WD40). Do you use straight water or do you mix in WD40/premix oil as well?


Thanks for the advice!

lOOkatme

I connect two separate vacuum lines together with a T fitting. I am feeding both service ports on the lower intake manifold at the same time. I have a long vacuum hose go inside the car where I rev the car myself and feed a gallon of water in a milk jug of just plain faucet water.

I warm the car up, connect my long vacuum hose with the hood up, I pinch the vacuum line and start the car. I run the car up to 3-4K rpms and I open the pinched vacuum hose and "sip" water from the jug while maintaining a 4K rev or something. I keep sipping it in increments till a whole gallon is gone. I then rev the engine for a while and let idle to burn off any water that is left. I suck through a little 2 cycle oil after the water is all burned. I then change the oil (obviously let it cool down and such), then I drive the car, make sure to get on it a lot, perhaps go to a track day or do some canyon roads and keep driving the car. over the next few thousand miles compression should hopefully improve.

RotaryLife99

What size tube do you use and what length should I buy when I go to do this? I might have my buddy help me with this, so I can rev it and he can keep an eye on the tube/water. Thanks again!

If carbon buildup is the problem that is causing these low numbers and this simple process fixes it, I will be very very grateful! I can't wait to try it out. I'll let you know and I might go back to Mazda and see if they can run the test again after this process. Maybe I can haggle for a free test because I don't believe they did it right the first time, but that's just my thought.