Compression test, ¿is it correct?
 

Hi, greetings from Spain. Please excuse my english, it is not as good as I wish. I read your forum from time to time, so I'm aware of the engine issues you are having there. Here in Spain we've had some engine replacements, but as far as I know, in a much lower rate than the one you are having (my dealer has done 3 replacements so far). Anyway, my warranty period expires right now, so I wanted to run a compression test just to make sure it is ok, although the car seems to run fine and haven't had any engine issues at all.

The tech said that the results were normal. He showed me a table (from a book which had all the min and max compression for all mazda motors) where I could see the results were inside the limits. But, the test was run at ~290 rpm (I have the new starter) so I don't know if the numbers are really on the safe side. I've checked with the graph on the service manual, and my results are below the "optimum" curve. The service manual states that minimum is 680 kpa at 250 rpm, but I don't know how this minimum translates to my numbers taken at 290 rpm. If you don't mind, I would like to post my results. I would be glad if you could help me determine if they are really right or not. Any help would be much appreciated.


The car has 35.000 kms (~22.000 miles). It is a 04 6 speed MT. I've been using premium petrol for the last months (here it is called 98 RON), first ~two years I used 95 RON. It had its third service done last week, so it has new engine oil, new spark plugs (all 4), oil and air filter, etc.

Motor was warm (10-15 mins after arrival at the dealer) and temp was about 30ºC (86ºF).

Here are the results:

http://img183.imageshack.us/img183/3...rotoresea6.jpg


Thank you very much in advance.

judging from the poor graph online that mazda provides, approx 750kpa is the minimum at 290rpm cranking speed. so while your engine is still in the "good range" it is at the lower end of the spectrum.

and wow... they are still using the WDS... the only thing nice about that thing was the touch-screen

All of the pressures should be way over 900 kPa at 290 RPM.
That absolute minimum at 290 RPM should be 788 kPa. Your engine is on its way out (provided the test was run correctly).

:(

So... is this a prelude to my engine death?

Is there any chance it will not go lower than this, or something I can do (driving habits, premixing, ...) to "save" it?

I don't really know what to do... It seems that it is in the bare minimum, so I think I won't be able to claim anything to Mazda.. What's worse, I think the techs here don't even know that running the tests at different speeds affects the results... so for them 800 is way over the 680 minimum...

Can I do anything other than wait to see how it dies? :( :(

well this is a tad on the unorthodox side and not condoned by mazda but... i have had some success with running auto transmission fluid through the engine while holding at about 2k to 3k rpms. get a long piece of vacuum line and fit it to one of the capped ports on the side of the intake manifold. insert a reducer or anything that will act as an orifice to slow the intake of the fluid into the intake. have someone hold the rpm steady as you SLOWLY dip the hose into the ATF and draw it into the engine. its tricky and can be dangerous. it will smoke like a train for a while and you will likely have to change out your plugs afterwards, but i have had it bring some engines back. try half a liter to start with.

use at your own risk

Thank you very much for your answers.

Charles, with "steam cleaning" do you mean driving it at high revs for a short period?

I'm not sure, but I doubt I have too much carbon-build up on the engine... I normally drive it hard at least for a short time almost every time I drive it (once it is warmed up). I used an injector cleaner ~5k miles ago too.

mazdatech177, is this method suitable in my case, even without having had any symptoms of engine failure (other than the test numbers, no power loss, stalls or bad idle) ? If this could solve the problem, would that mean that this issue is not a matter of engines tear down? (don't know if I said it correctly, sorry!)
The truth is that this method "scares" me a bit...

Thank you again, your help is very appreciated.

i understand what you mean PeriQ, i wouldnt use this method unless you start to develop low idle speed or stalling concerns. right now its "technically" not broken.
and if its not broken.. dont fix it

it will be an accomplishment for it to get past the "great expectations discussion phase" first

Don't bother.
Mark is so busy driving around parking lots at break-neck speeds (if that is possible in second gear) that he doesn't have time to explain his methodology.
He spends so much energy avoiding risk, how do you expect him to comprehend risk?

BTW - had an "interesting" conversation at Cobb this week...

Charles, it's not just you. There are people who try things and contribute by sharing their results, and there are those who pour liquid crap on the results that were contributed by others.
Just ignore it.

I think Mark and Jeff went to the same school. I find Mark very helpful if you ask him a direct question...Jeff as well.

Both have poor tolerance for BS....and show it in there presentation

Don't take things personally on here.......

Care to elaborate?

Ray- don't bother with Team. He's just trying to get a rise outta ya

I tried to help the trapped miners, but I ate all the KFC before I got to the site, so I just left.
I'm pretty sure I mentioned my "other" motives for my trip to SLC elsewhere. Mark tangentially sniped me at that time as well.

Here's Chewie at the Grand Canyon:

https://www.rx8club.com/attachment.p...1&d=1187161762

The descent into Marble Canyon at 120 MPH:

https://www.rx8club.com/attachment.p...1&d=1187162001

err don't want to bother but... back to the original message... I would like to ask one more question with your permission...

Despite having the latest flash, will it continue to get worse? Is it feasible that the engine holds on that numbers and doesn't continue to tear down? Or it has many possibilities of dying?

Thank you again.

Periq,

Back to your original query I would like to state two things:

1) The more time you run one engine the moe will get worn. That answers your last question: Yes, the wear figures will go worse as car miles go.

2) Manufacturers usually give wear figures with some margin, which means that you can usually run the engine with no problems after the "limits" are reached.

Having said that I do not consider normal that an engine gets worn at 22.000 miles. If I were in your shoes I would have a second compression check done (in a different shop, of course) to compare results. Find one where the techs can interpret and correct the data for different cranck speeds and draw to a final conclusion. If your guarantee is about to expire it is good to have a Mazda service document stating that the engine was almost finished @ 22.000 miles...

I just hope the new compression test figures are better.

Cheers

jird20