Compression test results on potential buy: Advice?
 

First post!

My wife and I are about to buy a well maintain 2004 with 130k miles, 50k on the engine (replaced in 2006). We've looked over the car, checked all the recall and maintenance history, and had a compression test done.

I'd like some forum pro advice on the health of the engine based on these results:

Rotor #1: 770/750/750 kPa at 276 RPM
Rotor #2: 770/780/750 kPa at 280 RPM

I did some quick math to try and convert it to the 10 pt scale, and got between 7.88 and 7.68 for each, but I'm not sure it that was right; the conversion I had was for 250RPM, and these were run 10% higher.

The engine seemed to have good power and idled with just a little vibration in felt in the shift knob.

Being over 100k, there is no more engine warranty. Are those compression numbers OK?

Thank you!

For how much?

According to the graph 750-780 kpa at 280rpm would be right at or just above minimum compression, right?

111.195599133 psi @ 280 rpm
I'd venture to guess that is around 100+psi @ 250 rpm. I agree with xexok's assessment. According to that chart, that is a tired motor.

Thank you for the input guys. So, based on the chart it is above the minimum compression, but should that significantly detract from the value (as in, will the car need a rebuild very soon, etc?)?

The negotiated price is $8,200. It is a Velocity red 2004 GT with 6-speedm 130k miles (50k on the engine). The car is in excellent shape inside and out. I thought it was a fair price, but you guys are making me nervous. Advice?

Tell them you are interested, but are worried about the condition of the motor, because its at the bottom end of the compression test results scale.

Look for another car in the same price range.
If you don't find one, get them to either replace the motor, or knock off more money so that you can budget in a motor replacement.

Either you get that car with a fresh motor, for less money, or you get a different car.

BC.

Do you really want to buy a sports car out of warranty with a motor that will fail soon enough? I wouldn't pay more than 6k for it, a engine replacement will cost you $3,000.00 minimum. You also need to think how much mileage is left on the tranny as well.

Thank you guys! Sorry this turned into a buying/pricing discussion, I had just meant to learn more about compression, etc.

The tranny seems to be fine, the clutch is less than 1k old. The rest of the car is all in very good condition (I love Southern cars!). We're going to negotiate on the price and will probably go through with the purchase. If we can get 20-30k out of the engine I think we'll be coming out well ahead, and who knows? We might get even more than that, or we replace the engine sooner. But then we can enjoy the car with a new engine!

You could find one with that price with lesser miles and has better compression results. Search is your friend, good luck. :)

I don't think you would get that. Even if you did, those miles would be with a weak motor. I think you might be able to do better. Rx8 prices have been extremely favorable to the buyer recently and winter is coming. Prices will drop more I think.

Exactly what he said, granted, I didn't pay any attention to where you were located, but I bought mine in early february 2011...138k miles, same exact color and model as yours and paid 7400 for it, got 28k miles out of it before the engine died about 7 weeks ago...and that was with eerily close compression numbers too.

I'd play hardball with that dealership...or just walk away.

This is a provate party sale... One owner, truly meticulously kept, and serviced at a good local Mazda dealer.

I am near Atlanta. I have thoroughly searched and sure, maybe an oddball car comes up cheap in California or Maine, but factoring in inability to inspect in person and/or travel and transportation costs, I don't think I can do much better unless we hunt for weeks. Unless it fails emissions or the final check goes bad, I think we'll go for it.

Run away, run away ....!!!

although it seems like the numbers are a bit low, did they decarbon the engine and tried it again?

Its your call, just do not get trapped in this deal because you think "there are not any more rx8s around me". If you find one across the country you could ask a local member on these boards to check it out for you, some may be willing to help you. Also shipping a car is not as expensive as you may think.

I just cant help but think a "hesitation, loss of power, how long will this engine last??" thread is in your future with this car. At least do the decarb with mazda and then run a second compression test like jason suggested. It might cost you $200-300(unsure of prices) to do it, but its better than a possible $8200 mistake. If you have no problems with waiting for the engine to die and then replacing it then go for it, if its in your budget.

How do you know the car was meticulously kept? Is the owner on 8 club? It's easy to clean the engine bay, exterior and interior once and call it a day. It's harder to do the the right thing and do the correct maintanance everday. Pass on this. Why did you even post up if you were going to snatch the car up despite the advice? If you know you are going to change the motor out soon (which I think you will) then buy a car with a blown motor for cheap and buy a new motor. Hell buy a ported motor. Don't be impatient when shoping for a rotary because in the end, you will pay or even worse, you will have to wait a long time while your car is serviced and there is nothing worse than that.

^:worship:

Thanks again for all the input guys!

Although I have gone forward with the purchase, don't think I didn't take your advice into consideration. I was able to negotiate the price down to a point I am comfortable, even knowing that it may need a new engine before we sell it.:fingersx:

It is not our DD, so it can sit in the garage or shop if need be (most likely, when I start tearing things apart and start playing with it!). In the end I'm very happy for what I paid, and that's really all that matters. :D:

I'll be posting pics in the future in the appropriate forum, looking forward to joining the community!

Well welcome to the club. Did you ever get the decarb and try another compression test? I'm interested to see if if made a difference. Good luck dude.

How much? I hope you can get an s2 motor in there. That would be ideal.

Wouldn't that also need the s2 pcm, and be a real pain in the ass? Not saying its not possible, just super expensive unless you find a s2 that was totaled from the rear end, right?

Ash8 and myself both have threads on that subject. It's not feasible for many reasons.

That engine is junk.

6K or walk. That's all I can say.

and prepare another 3K for an "ok" Reman from Mazda. 4-5K if you want a "decent/excellent" rebuild.

7-8K for a "Brand new and Excellent" engine.

unless you wanna dig every single pieces of wire out and put them back ...

or should I say

unless you have too much time to waste...

Yea I didn't take time to look at 9k or ash's thread yet but I'm sure it would take a ton of time or a lot of money for no gain at all. The only gain people see is unproven reliability of the new engine.