RotaryRider

Problem & Symptoms: There wasn't really a major problem. My car started fine when cold within 1 to 1.5 sec when hot it usually takes about 1.5-2.25 to fire up after cranking. The other day I took a 300 KM trip, took a short stop (10 mins); when tried to crank it fired up but took slightly longer than usual (I'd say about 2 secs) cold start. Therefore, I decided to get a compression test for my peace of mind (which backfired miserably )

The Test: Next morning, I booked an appointment at my nearest Mazda for a compression test. As usual, read a lot about compression testing and did my homework before going in. I showed up at Mazda and went straight to the service manager, asking him in what form I was gonna get the final results, 2 RPMs and 6 Numbers; 3 for each Rotor. The manager says, "I am not sure how they do it, I am not a tech but I will pass on all the information I get." I tried to reaffirm by asking if they are gonna normalise the numbers and compensate for altitude (as the city I live in is 1100 feet above sea level). He said he's not sure what I mean by that.

The Results: They took the car away for approximately 90 mins and came back with a set of numbers I was expecting.The numbers are as follows:

Rotor 1: 7,6.9,6.5 at 253 RPM
Rotor 2: 6.9,6.3,6.9 at 252 RPM

I asked him about the compression test procedure and whether he compensated for the altitude. He said that he took the numbers from the tester and plugged them into there 'internal website calculator' to get the final number. At the top of the page he printed out it 'PC calculator2_5_7_07.xls'. I believe this excel file does not take altitude into account. The page looked exactly like this one (example):

Link: http://www.underway.us/rx8/bog/rx8_c...on_oct2014.pdf

Decoding the Results: According to my understanding they probably did not normalize the results as the RPM number are 253 and 252. So I am assuming the altitude was still unaccounted for which gave me a little more confidence. Then I used Foxed.ca compression calculator to get the adjusted numbers. Foxed.ca says:

Rotor 1: 7.49,7.38,6.95 at 250 RPM approximately 1100 feet above sea level
Rotor 1: 7.40,6.75,7.40 at 250 RPM approximately 1100 feet above sea level

I know the numbers are not very encouraging. Rotor 1, face with 7 is borderline and Rotor 2, face with 6.78 is below specification. But my car is still running fine for now; as I stepped out and cranked it fired right up in under 1 sec.

My Questions: 1) How long before my baby dies ? I understand it can be a day or a year, don't give me that answer, I would like to know from someone who has experienced this on how long it took.

2) Do they always decarb before a compression test ? (I will call to confirm tomorrow if they did that in this case.)

3) What should I do to prolong the leftover life on my baby ?

4) Any magic solutions (that actually work) to restore some compression ?

5) Your opinion and advise on the results ?

Specs: 2005 with 60K miles, bone stock.

Jastreb

iTrader: (1)

Sorry to hear, similar thing happened to me recently.
What are the units on those compression numbers. Some dealers use kPa X 1000, some use kgf/cm^2. If the units are kPa x1000, the compression in kgf/cm^2 is just a little bit higher. Not that it would make that much of a difference.


2) No they don't typically decarb before a compression test. In fact if they did, the compression would be lower immediately after a de-carb. It would be several hundred miles before you might see a compression improvement.

3) Pre-mix, make sure ignition coils, plugs and wires are fresh.

4) Some members reported a slight improvement after a de-carb. They should chime in.

5)How many years/miles on your car? Maybe you are still under the extended engine core warranty?

Good luck!

RotaryRider

Thanks for the quick reply bro.

The units are Kgf/cm^2

I am inclining towards decarbing to see if it helps but I don't want to lose more compression and end up with hot start problems.

Unfortunately, the warranty ran out at the end of last year

TorontoRotaryGuy

Hello guys. I'm buying a stellar 2011 R3 RX8 in Toronto. it has 15,000 kms (9000 miles) and was a Mazda Canada corporate vehicle for most of it's life. I'm buying it from a Mazda dealer, that had a hard time letting it go, and were using it as a showpiece. I think it's one of the best examples you can find. I still asked for a compression test, after reading all of the horro stories. Below are the results. It looks amazing - almost too good. The compression is very high. Any comments?

2011 Rx8 compression test, performed Jan 7, 2022

Loki

iTrader: (1)

Ok but it's literally a month or 10 years. One person's experience and mode of failure doesn't predict what your experience and mode of failure is.

That said your car is fine. It will eventually need a new engine, if you make your peace with that, the exact timing is less important. Retest in a while to see if you get the same results. My car has been hovering in the same range of 7s as yours for the last 6-7 years, up and down a bit with each test. Premix and keep an eye on the rest of the usual rx8 weak points.

alterego

If you have the mechanical capacity to rebuild it yourself or want to remove it and send it off to someone you trust, you could save yourself from having to replace housings or rotors when that low face breaks loose.

TorontoRotaryGuy

Thanks for the response. The compression numbers on my test actually seem too high. Do you know what could cause this?