Hello folks,

I have a 2008 RX8 which I bought brand new. It now has 49K miles. I have taken very good care of it (regular oil changes, topping off, and all scheduled maintenance). Last week I got new brakes and rotors and while at the shop I also got compression check done. Here's the results;
Rotor 1: 6.4, 6.4, 6.9
Rotor 2: 8.6, 8.1, 8.2

I don't remember the rpm, I think he said he normalized to 250, but need to confirm.

So, can the compression differ so much? Why?
How long do you think I have before a rebuild or a new motor?

I don't see any issues and the car is running strong and tight. Just a few months ago this has become my daily driver. I drop my son at the daycare and go to work.

Please advise. Should I be worried about its reliability now? Rebuild or replace proactively? How much would it cost?

Sorry about so many questions. I'm just panicking.

Thanks!!

 

the difference happens sometimes. eventually plan for a motor but unless you are gonna have it rebuilt vs. getting a mazda reman i would just drive it until you experience more problems. your #s arent that bad. a mazda reman is ~3500 plus 1000 core charge

 

No need to panic. Your car runs fine, so that's a good start.
Yes it can vary that much, though this is unusual.

There is no answer to the question of how long, but you'll have ample warning signs. These things don't up and explode one day, it will become harder and harder to start while warm, which is a nuisance, but not tragic. Once that starts you can look at your rebuild options.

Might be worth getting the test done again on a future oil change. My compression has gone up and down through the years and through different testers.

Are your ignition coils fresh? If older than 30k, replace. This is not in the maintenance schedule, but dead coils are too often the root cause of engine problems.

 

@2000sh Thanks much for the quick response. I'll keep driving my 8 until the engine shows signs of its nearing doom. Hopefully, that day is not close by.

Does Mazda make completely brand new engines for the 8 anymore?

Also, what could I have done wrong, in terms of maintenance, for the low compression numbers at this relatively low mileage?

Is there s possibility of the test being wrong on that rotor?

Thanks!!

 

@Loki Thanks for the reply. GIves me some hope

I was imagining my engine stalling while going with my son on a long drive (BTW he loves my 8 :D). So that's not a worry now.

Sure, I'll try to get the test done again, later, from a different place - just in case, to be sure.

Yes, ignition coils and plugs are relatively new. ~10-11K miles on 'em. I might have pushed the original coils a little bit (couldn't afford coils when I wanted to replace them at ~30K miles. I think I changed them around 38K+ maybe). So that could be one potential cause?

 

Mazda remans use a lot of, if not all, new components according to a teardown done by Mazmart. Made in Japan by trained technicians as well. Pretty good value for $3k + core.

 

I agree with Loki, I wouldn't worry about it. I have driven rotary engines with blown rotors. Being a little down on compression at 250 RPM is almost negligible at 3k or 4k RPMs. As long as the car starts and drives normally, I wouldn't give it a second thought.

I would only worry when the car takes noticeably longer to start when the motor is hot/warm.

 

I share the sentiment to not worry. Continue to enjoy your RX-8, and when - and if - you start having low compression issues (i.e. hot start problems), look into a a Mazda reman engine. That’s my plan; I consider the $3-5K cost on an 8 in otherwise excellent condition to be a relative bargain for what you get in return. It’s not a popular opinion, but I really do feel like I’m secretly driving a $60-90K exotic supercar for, well... peanuts. I know, crazy.

Also, kudos to you for staying on top of your car’s maintenance. If all owners showed their 8s the same love and care, I suspect the car would enjoy a much better reputation for reliability.

 

I'm not sure which rotor is 1 and which is 2 in your case, but the rear rotor will often fail first, if the catalytic converter becomes clogged. You might have your cat visually inspected for clogging and have your ignition coils tested. They often last less than 20K miles, which leads to cat clogging, then rear rotor damage.

 

@UnknownJinX Thanks! I did not know that most of the components can be brand new. That's good to know. I thought only the apex seals are new and the others could be from different motors.

@strokercharged95gt Good to know. And yes, it starts and drives strong and no issues with hot starts too, for now.

@New Yorker Totally agree with you. None of my friends understand why I spend so money on a car which doesn't cost as much to buy used. I feel the same as you; driving around in a cloaked supercar of sorts.

 

@Steve Dallas I am not sure either, which one's which. But, now that you mentioned the catalytic converter, I recollect that one day a couple years ago I was driving to work and I saw the check engine light on briefly and I experienced loss of power. I straight away took it to rotor sport (in Santa Clara - a reputed place around for the 8 owners). I was told I will have to replace the cat, which I did. And if I'm not wrong, I think, I replaced my coils and ignition in the same visit. Could that incident indicate that the lower numbers are from the back rotor and the cat was the root cause for it? I am actually much more relaxed now (than when I posted the message), after seeing all the messages above, but still couldn't sleep properly last night and am slightly agitated about why this had to happen to my 8.

I think I'll get over this feeling in a day or 2, hopefully.

 

^ A flashing CEL is always a misfire, which usually means something is faulty in the ignition system. When fuel and oil do not burn completely, residues build up in the cat and clog it. The backpressure and heat from the clogged cat kills the rear rotor pretty quickly. With that in mind, it is possible that event affected your engine, but it is impossible to be sure. And, we are not even sure of your rotor numbering, so it could be your front rotor that is low on compression. That is the typical failure cascade, however.

 

@Steve Dallas I got a reply from the shop late last week that rotor #1 is front and #2 is rear. So things are going bad in the correct order; not sure what to take out of that though