PNWDad

Have a lead on an '06 RX8 that's near my folks' place in the country. It's a long way from anywhere, let alone any place that can do a proper rotary compression test. I've hunted... So, I've talked to the owner: regular oil changes, on top of coils and new starter aways back. Sounds pretty much stock. Says no cold or hot starting issues at all. ~100k on original engine. 2 owner. Right now taking him at his word and going to see it, but without being able to do a proper compression test, whats the best I can hope for in checking it out? This will be my first one, read up a ton, and interested in this car, but have read basically everyone swear by getting a compression test before buying. But if I can't feasibly do that.....? Any ways I can get reasonable assurance it'd be average or better based on inspection and driving? thanks!!

Shaozhou Zhang

Compression test with a piston engine tester and normalize it, Driven by Madness has a video about it.

There’s a thing called engine vacuum testing, read more here https://www.rx8club.com/series-i-tec...esting-147135/. Some dealers use this in addition to compression test to determine engine health.

If both cannot be done, at least a video of cold and hot start is somewhat helpful.

But if you are unable to get a proper compression test it is advised not to buy it. Start cold and hot does not mean a lot. My car has borderline compression but it starts amazingly, super fast.

Loki

iTrader: (1)

Check how well it starts warm.

At the end of the day it's your money and your risk. If you're convinced from the available info that it's not bad, and understand the eventual engine replacement cost (which could come this year or next year or in 10 years), and the price is right, nothing says you can't buy it.

.If you're stretching your budget for this car, then definitely get one you can be certain about. Or a known dead one for cheap with a plan to replace the engine immediately.

mazdaverx7

iTrader: (6)

Loki really gave some good advice. Hit the nail on the head really.

You will want to plan for an engine replacement in the future. That's just the nature of the Renesis engine. Expect it to be on the lower end of the spectrum with 100k miles and allot a budget for a rebuild or reman engine. If the car has been well maintained and is in good shape, it would definitely be worth putting an engine in down the road. Go into the purchase knowing that however, and be prepared to work on the car yourself and be able to learn to diagnose issues should they arise.

alterego

In my experience, I have found 2 indications of low compression even if it starts fine hot or cold.

1. When driving on a flat road with cruise control on, the car will not be able to hold a steady speed and will bounce either up or down constantly in an effort to keep the speed you set

2. No acceleration under load in higher gears, lets say from 3rd above 6,000 rpms into 4th. You will feel a distinct lack of power

mikeljourdann

Why not just spend the like $300 or whatever for the Rotary Compression Tester and just test it yourself? Then you can give compression tests locally and recoup your funds if you want and there's no one around, lol.

Ricky SE3P

iTrader: (10)

I just want to say that I replaced a motor in my car with low compression, like EXTREMELY LOW, and somewhere I have videos of it both hot-starting and cold-starting perfectly fine. Its ability to start isn't always a proper reflection of the engine health. Compression testing with a tester from a piston engine is no help either when it doesn't record the engine RPM which plays a major role in the proper calculations. My raw numbers on the compression test were in the upper 90's, but the starter was spinning over 320 rpm. Normalized it was well below failing numbers. Buy a compression tester, you'll be able to use it on your eventual rotary every 6 months and write down/record the numbers as part of monitoring engine health over time which would be a good practice. Its one of my favorite tools in my toolbox for that reason.

Also if you compression test this 8 and it fails, and you end up not buying it... you can use the tester to compression test the next 8 you look at. Repeat this process yourself enough times till you find a good one and get a deal for it and the tester has already paid for itself pretty much.

What do you do if you cant compression test? Walk away. Or buy it under the impression that it needs a engine replacement and pay a price that reflects its value as a rolling chassis since you cant be sure what engine parts if any will be in reusable condition for a rebuild.

CaymanRotary

I mean generally, as long as the car runs and drives and you did the tests as mentioned above, compression likely isn't an immediate issue. Everyone is right, a proper rotary compression tester is the only real way to diagnose engine health. However, through my experience as well; the tips as mentioned above will rule out compression being at least an immediate issue just by driving the car.

MincVinyl

If I was going to buy another rx8:

• I'd make sure to start the car (should be near instant start since a cold engine will have better compression.....note what rpm the engine starts at 250rpm==stock starter 300+==upgraded, rotary engines gain compression with rpm........it is possible to hide a lower compression motor by using a faster starter)
• shut it off after a minute cold.....see how it starts again.
• Wait for it to get to idle temp, shut off, start again.
• Then go on a test drive all through the rev range, which shows if the intake manifold valves open smoothly and if the fuel pump fails at high rpm (note the temp gauge is a dummy gauge so likely this will get the car fully up to temp even if the gauge doesn't move)
• shut off and restart. (This is the basic hotstart test for low compression, longer time generally means worse compression. No start = rebuild)

I'd consider the engine worthless if you can't do this without any troubles. Now even if it passes, this isn't to say the engine will last but it is a decent indication of whether you are buying a complete brick or not. Keep in mind engines may keep compression depending on the owner anywhere from 70k-130k miles(housings/seals/rotors?/bearings? rebuild). The stock coolant seals can go anywhere around 100k miles(seal rebuild+ housings?) there is no way to really know when a coolant seal is going to go.

Replacing the starter and coils is a good sign. The stock coils typically give up at 30k miles.....leading to a clogged Catalytic converter.....leading to heat buildup in the header.....leading to increased wear/ blown seals/ damaged coolant seals. I advise asking about the Catalytic converter, many people remove these which may show an engine code and fail obd2 emissions tests.
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Buying the 300$ rotary compression tester is your best friend if you truly want to buy and own an rx8. No matter what plan for a rebuild or new engine upon buying the car, you never know how the previous owner trashed it.

Jerakl

Stall the car a couple times once it's warm, and if you can drive it again within <20 seconds it's probably good :P
(Do not do this).

From what I've heard how well it starts up once the engine is warm CAN be a reasonable estimation of the engine's compression.