MHONZDA

I checked this car out and the owner had kept it in a near flawless condition. Started up cold just great. Only turned over for a second. I test drove it and got back. It was warmed up. I turned it off and started it three times. Each start up was just as good as the first time...

The engine was replaced by Mazda about 16,000 miles ago when the car had about 56,000 on it at that time. It's a 2005 6-speed. I don't have my butt dyno calibrated to know how quick an rx8 should be, so I don't know if there is any loss of compression.

The was never any smoke from the exhaust that I saw but I didn't stand behind the car when it was running. It was T-shirt weather too.

The owner seems pretty knowledgeable about rx8s, but the car is completely stock and they never premixed the gas.

Is there other things I should check? I feel like the engine is good.

NotAPreppie

Completely mandatory.

Treat an RX-8 without a compression test the same as an RX-8 completely missing its engine.

Red line envy

+1^. I bought mine in 2015 and it was fine started hot or cold but yet a year later I was ripping the engine out. (just finished putting new engine in now)
So save yourself a headache and get the test

mazdaverx7

iTrader: (6)

As of right now it sounds as though the compression is pretty good! But I would perform a proper compression test to determine the engine's health. You may have one face that's lower than the others by a good margin or by you may find that the engine is in great health with not much difference between each face. You just need to know where you stand honestly.

Steve Dallas

Absolutely mandatory. Also get a block (exhaust gas in coolant) test done. I just had my engine replaced at 45K miles. It always started right up and otherwise showed no signs of failing compression. But, it failed both block and compression tests.

MHONZDA

Thanks for the responses guys. I'm going through with the compression test. It's good to get that "peace of mind".

I also think I'll use the results to compare with a compression test I'll try at home using a normal piston engine compression tester. The method is shown in a YouTube video by DrivenByMadness.


Has anyone verified the accuracy of this method? It would be interesting to compare to the real results from Mazda, and see how close the results are. Then maybe in the future I could use it to determine the health of the engine a bit more cheaply?

Also about how much does a block test cost? This is the first I've heard of it. Do they just test the coolant itself for exhaust particulates?

schumithecat

to me it depends on what you're paying and how much you need the car. I didn't get one becuase I paid peanuts for mine, the owner had taken good care of it, it showed no signs of low compression, had pretty low mileage on engine (40k on mazda reman; first one lasted 90k), and it is a weekend car so if I had to swap engine it would not leave me without a car for weeks. to me if the test is good, it would justify the seller raising the price since the uncertainty lowers the price I would otherwise pay.

MHONZDA

Thanks for your contrasting opinion. I think I'm mostly in the same boat as you were, but I'm not really paying peanuts for this rx8. I sure hope a good compression test doesn't make the seller raise the agreed upon price!

NotAPreppie

If I understand that method you have to...

• Use a normal piston engine compression tester with the schrader valve removed.
• record the dial face (preferably in slow motion) while cranking
• Use a computer to read the pressure measurements and calculate the number of pulses per second.
• Do some basic math to convert number of pulses to RPM.

Theoretically, this could work if you don't want any precision in your measurements. Also, the length of the tube from the spark plug hole to the gauge will reduce the apparent compression results (more volume for gas to fill) relative to a real rotary compression tester that has an electronic transducer in the spark plug hole (read: no extra void volume).

Just take the car on a test drive to a Mazda dealer and pay them the 1-2 hours of labor to run the compression test. Make sure you and the seller agree upon the price before the test.

New Yorker

Personally, I would not buy an RX-8 without a rotary-specific compression test from a Mazda dealer or from a reputable, independent rotary engine mechanic.

Yes, mandatory.

MHONZDA

What do you all think?

MHONZDA

Ok i tried to post a pic of the data sheet but it says I need to wait for moderator approval.

So these are the numbers:
Rpm: 166
Rotor 1: 498, 501, 524
Rotor 2: 560, 560, 558

"Compen. (250rpm)"
Rotor 1: 709, 712, 735
Rotor 2: 771, 771, 769


Seems there is quite a difference between rotor 1 and 2. What do you all think?

Nopstnz

Passing numbers, I don't think that difference is that severe, I have seen way worse.

Go for it, I am sure the price is good if it is an 05

NotAPreppie

Use the chart in this post.
Find the pressure value.
Follow that row until you get to the RPM.
If it's in the red, it's bad. Green is good. Yellow is marginal.
https://www.rx8club.com/rx-8-discuss...0/#post4551182

It's not uncommon for one rotor to be worse. Usually it's the rear and my hunch is that it's because it doesn't get the best cooling.

The fact that the test was run at 166 RPM means that either the battery or the start is ****. It probably has the old, weak starter.

MHONZDA

I'll just post a little update so I don't leave you guys hanging. I was originally hesitant on the compression test largely because of the price. I was quoted about $145 an hour for 2.5 hours plus tax, which works out to be almost $400. For the price I was paying this was a significant increase in cost. After getting the compression test, the bill was only like $230. Much more reasonable in my mind! So a happy ending there.

As for the starter, yes it does seem to spin slowly, but it does still start the engine without fuss. I ordered an upgraded starter anyways. One I found on Amazon:


I haven't installed it yet but will soon. I told my girl that I'd teach her how to drive stick in it, so I have to have a strong starter!


Also, I'm thinking about starting an introduction thread! I have a lot I could say about this RX8 and I've only had her for a week! Should I start that thread in the New Member forum or in the General Discussion forum?

mazdaverx7

iTrader: (6)

Keep us updated on how the starter works. At that price point it seems like a good buy! Feel free to post a thread about your car in the New Member section if you'd like. I post all of my restoration threads and pictures in the RX-8 Multimedia/Photo Gallery section. Would be cool to see pictures of the car and hear about its journey and previous history!

Steve Dallas

Some dealers have become very proud of their compression tests. The actual test takes 45 minutes, if the car is already hot. I had a dealer quote me 2 hours as well. I rattled off the procedure, and the service manager sheepishly reduced it to 1 hour.

Votewiggum

I am halfway between Madison and Milwaukee, and have three dealers to choose from. The first two dealers seemed to stumble a bit and had to do a lookup of the compression service. They both quoted me $350 and $450. The third dealer said "I haven't had to use that tool in awhile, I love those cars bring it in, and we can have it done in 45 minutes." His cost was $145. So, my choice seemed pretty easy. If you have an opportunity to shop more than one dealer, it may be wise to call around.

Tr4

100% percent neccessary. Always perform a pre-purchase inspection before buying any used car.