Hi I'm looking to buy a 2009 MT Rx-8 from a local buyer. He performed a compression test earlier in the year and gave me these numbers
Front: 700kPa, 710kPa, 710 kPa at 284rpm
Rear: 690kPa, 700kPa, 710kPa at 286rpm
The care currently has ~40,000miles. From the charts I have seen, these number are pretty borderline. The owner said it passed according to the Mazda dealer. Does this mean the engine could fail soon or do I need? He says he has been following maintenance schedule 2. He adds about 1/2 quart of oil every 500 miles. Are there more specific questions I should be asking?

Thanks!

 

It is a borderline engine. 690KPa is technically failing. The engine is starting to lose compression, and compression loss tends to accelerate after a certain point, but it is unpredictable from what I have seen. It could last a few months or a few years on those numbers.

Additional questions could be whether he knows the health of the catalytic converter, how often he has changed his plugs, coils, and wires, whether he premixes, etc.

 

Steve's gone over everything I would have said. Unless you are ready to budget for a rebuild, or you can argue for a reman (which is truly **** or miss, remans fail just as often as older engines do) your better off finding one that's got healthy compression and a really rock solid schedule as far as work done goes. I bought mine on a whim and by pure luck did I get a car with decent history and good compression. It ain't great, it'll fail at some point in time, but I'll be ready for an engine by then and hopefully have something nuts ready to go.


I'd pass and go for one with better compression. That's me, though.

 

Thanks for the reply guys. Sounds worrisome, I really wanted to like this car. I asked him a few questions and his reply was "When our dealer ran the test they called Mazda corporate and were told that the specs were passing, just on the low end of the spec..

Ignition coils were replaced on 6/17/2015. Spark plugs were replaced on 11/05/2012 and again since then but I’m having a hard time finding the exact date and paperwork for that.

We don’t know the health of the catalytic converter but we don’t have any reason to suspect any issues with it."

If I were to negotiate the price, how much should I have in hand to rebuild the engine? I have seen the number $2000 a couple times and was wondering if this was still current. Also, what would it take to have the engine replaced under Mazda warranty?

 

For Mazda to replace the engine, it has to score below passing in the compression test. Being a 2009, you have under a year of warranty, depending on the first purchase date. If it was bought January 2009, obviously that's less than a year. You could make a bet that it fails before the warranty runs out and shoot for a replacement engine just before then, which, if it works out, means you're set for a long time.

If you have to replace the engine with your own money, budget 4-5k. All depends on how much work you want to do yourself. It's usually recommended to buy a ready rebuilt engine from a reputable shop like Pineapple, Pettit, RotaryResurrection, etc rather than trying to rebuild it yourself. If you can install the engine yourself, you save money.

 

I'd only buy that if it was cheap enough - you might be able to extend the life of the engine by adding a little high quality premix to each tank and most importantly, drive the car like you stole it, but ultimately you'd have to budget for an engine refresh.

 

Good advice thus far, but yeah it's borderline. Being an aged engine that is now hitting these numbers it is concerning... however, if you can budget for a rebuild and can negotiate them down in price, you could still get some life out of that engine. You just have to be realistic, that you also might not.

Obviously that chart shows the 280 crank speed, but if you have your sea level reading and want to normalize them down to the widely used 250rpm, here is the calculator for that...

Foxed.ca - Rotary Compression Calculator

 

As for rebuild cost, it depends on the engine's health when opened up. I think a general seal replacement kit runs around 1400$ + builder's labor costs, so yeah you could see a rebuild around 2k$... but if you have any damage or unusable components it would obviously be more. I have seen quite a few fresh rebuilds being sold for 2500$ So I might budget around there just to give yourself some wiggle room.