jmcho

I've been calling up shops and asking them to run the pre-purchase inspections for this 04 rx8 gt 77k miles, and it seems like none of them want to do a compression test.

What i'm interested in knowing is if a compression test is really a requisite of buying this car? If the car sounds fine, and runs good would a compression test be able to tell me it's not?

cmc

well I am a new owner and no expert but I talked to a guy on base in Norfolk that has an 8 and he said he had compression test done two years ago and the number indicated his had no compression, he didn't have money to fix so he has been driving ever since and experienced no problems. may be rare case im not sure. I had one done on mine but didn't do until after I bought because I didn't find this forum until after. sorry I know this didn't answer your question

Arca_ex

iTrader: (10)

Yes. Get one done. Especially on an '04, they have no warranty so if the motor goes shortly after then you're SOL.

bose

iTrader: (5)

True

Coldwound

iTrader: (1)

No more important than the car itself.

BigCajun

iTrader: (1)

The reason some may be reluctant to do a compression test is that mainly dealers and shops specializing in rotaries have the equipment necessary.
There are 6 different #s that check each face of the rotors that will tell you if it's good.

Read the new owner stickies(!!!!!) and judge for yourself.
If you don't get one, you are taking a huge gamble.

9krpmrx8

iTrader: (46)

What feels good can be misleading, and more so to someone who has never really driven an 8. An engine that is borderline low on compression may feel fine. Compression tests are smart move when buying any car, but even more important when you are buying a 10 year old rotary.

And I come from a long line of Hondas and Nissans and I can tell you it's common for an engine to feel great just before it blows.

monchie

Compression test is a MUST when buying a used rx8...

Coldwound

iTrader: (1)

DONT get a compression test done... when the motor blows and you realize you dont want to spend the money on a new one Ill come take the shell off you hands

jmcho

Ahh thank you everyone for your input!

I scheduled a compression test with a dealership to be done for $130.
I'll be sure to post again if it works out in the end.

Again much appreciated!

nycgps

iTrader: (1)

no compression? they were doing it wrong. they probably never seen what a no compression engine runs like (I have one right now)

he can drive a low compression car all he wants, it's just that it will run like ****, well, most people can't tell cuz they don't give a **** about their ride.

RIWWP

iTrader: (2)

I'm sure with a bit of effort we can dig up dozens of threads where new owners first post is about a blown engine and trying to figure out how badly screwed they are...

FrankieAvocado

That's not too bad, I ended up paying a Mazda dealership to have mine done and it cost $200. Nobody around would run a compression test on the engine for me except the dealership, total pain. I hope everything works out for you!

alnielsen

iTrader: (4)

It takes specialized equipment to test each face of each rotor. There was a home unit that was made at one time, but I don't think (99% certain) that it isn't available any longer.
A standard compression tool can be used by removing the shrader valve. But, it will only give you the average compression of the three faces of the one rotor. If you have one face that is bad, it may go unnoticed.

jmcho

Hey everyone,

I'm about to head out to get that test done.
If the results end up low, or maybe even near the point of considerable failure, what are some of the things I can do to improve it? Other than replacing the engine, I've seen that redlining, seafoam, pre-mix all help when it comes to compression. Anything else I'm missing?

RIWWP

iTrader: (2)

It depends on the reason. If it's due to physically worn seals, then you can't add the metal back on. Rebuild or replace is it.

The only other option is if it is due to carbon caking that is either holding the seals out of position or preventing them from sealing well. In that case, a decarb may help. I recommend you read through my decarbing picture thread before you do a decarb though, just to educate yourself on what is actually happening inside the engine.

Schenags

Compression readings. Thoughts?
2008 Rx8 35,000 miles

Cold
Rpm: 250
Rotor 1: 7.5, 7.1, 7.3
Rotor 2: 7.6, 7.4, 7.6
Rpm: 257
Rotor 1: 7.7, 7.3, 7.4
Rotor 2: 7.7, 7.6, 7.8

Warm
RPM: 250
Rotor 1: 6.2, 6.3, 6.1
Rotor 2: 6.7, 6.6, 6.5
Rpm: 287
Rotor 1: 6.9, 7.0, 6.8
Rotor 2: 7.4, 7.3, 7.2

NotAPreppie

Ignore the cold numbers. They are meaningless.

Use this chart:
https://www.rx8club.com/rx-8-discuss...0/#post4551182

Find the compression score in the appropriate units on the left side.
Follow that row to the right until you reach the RPM that the engine was turning.

If it's in the red area (above the black stair-step line), the engine is no good.
If it's in the green area (below the black stair-step line), the engine is in good shape.
If it's in the yellow area (near the black stair-step line), the engine is marginal.

UnknownJinX

If you are close to the sea level, this engine is officially failing.

If you are at a place with some altitude, you need to account for that as well.