Compresion drop in the last year
 

Here are my test results from last year compared to yesterday. First numbers are raw results, second are adjusted for dead space and RPM
Note: These are from a TR-01 compression tester which apparently scores an avg of 12% lower than the Mazda tester. I tested each rotor 6 times and took the mean results (front first, then rear, then front again for control)

Last July:
Front: 111 - 109 - 113 @ 275 ==> 108 - 105.9 - 110 @ 250
Rear: 110 - 113 - 114 @ 268 ==> 108.9 - 112- 113.1 @ 250

Yesterday:
Front: 108-101-102@264 ==> 108 - 101.7 - 101.8 @ 250
Rear: 113-111-109@251 ==> 117.1 - 115 - 113 @ 250

Mazda Specs:
It's not a major drop, and I am still within the Mazda acceptable range, but the front rotor has always been weaker than the rear and now it's gotten weaker again, at least one rotor face has dropped about 6psi and is closer to the fail mark.

Engine only has 42,000KM on it (26k miles) and has had an OMP adapter installed running Idemitsu premix for the last quarter of its life, additional premix of 4oz/tank (8oz on track days), redlined daily (only when warm) and subjected to DD, AutoX and some light lapping. Running RP 5w30 since the OMP was installed, dino 5w20 before that, always changed at ~5000km (~3000mi) and using the K&N HP-1010 filters (extra long).

I know that my plugs need to be replaced, which I plan to change, but I'd like to prevent this from deteriorating further. Would the Mazda Zoom Cleaner be of any help here (similar to Seafoam)? Not quite sure what else is possible to do here.

Yes, I did this immediately after I got home from work. Car was very hot.

I am unsure of the intake idle vacuum, assuming I can read that with the AP (?) but my AP is on its way back to Cobb for warranty repairs. Should be a few weeks 'till I get it back. I'll see if anyone I know has a vacuum gauge.

Altitude is ~260ft.

I'm only at 90 ft MSL. It's like I have Nitrous. ;)

New Orleans has oil premixed in their air though....so....yeah.

ZING! :lol:

Back on topic:
Humor me and check to see if you have any oil drips from under your engine.

You know what....worst come to worst, just light all the damn stuff on fire :D:

is puzzling? I dont get it. One rotor actually has increased compression@250rpms and the other has lower from the previous readings?
I would suggest using a heavier wgt oil and what engine temps are you seeing? Have you ever had over 220F for any lenght of time?
Mazmart oil pressure regulator mod is also good imho.
OD

Alrighty sorry for the delay, finding a vacuum gauge was a bitch here.

Vacuum is just a tad above 16mmHg @ 260ft, hot engine, measured at the VFAD inlet below the UIM.

No leaks that I can see. Oil level is constant (one advantage to the OMP adapter, oil level doesn't change!).

I did go up to 5w30 - are you recommending 5w40? Temps in Canada aren't as harsh as the US, though it may help when I track it.
While I don't have a dedicated temp gauge the one in the dash has never read higher than it normally does. My stock oil pressure gauge is busted though so there may be variances there that I'm not aware of.

Well not much choice here just keep driving it and get a Mazda compression test before the extended engine core warranty expires. If your numbers are right the engine is on it's way out. All Rotary wear over time but it does looks like your going fast there. I know the Tester conversion math is probably fine but I would want to see the Mazda test results if it was my ride.

^^ presume you were speaking to your coolant temperature gauge as being nominal. You do realize that the stock oil pressure gauge is a binary have pressure/have no pressure gauge?

I would recommend 5w40 when tracking - but hard to find so actually 10w40 as presumably it's warmer weather tracked.

It really is nice to have dedicated coolant temp/oil temp/oil pressure gauges, especially when tracking as you can tell at a glance if you're moving outside normal operating conditions.

I have no warranty on mine as it's branded rebuilt. :-(

That's why I'm trying to prevent as much as possible. If it does go though I am flying a certain someone out to do a port and polish + rebuild :)

I do intend to get a set of gauges... waiting on a certain GB to start for a new gauge pod.

Why and how are these compression rates adjusted down to 250? Mine was at 273 and I was told that was used because that was how fast the car actually cranked over at. I was told they then use a table to figure the ratio based off that. I ask them about 250 and they said that different cars turn over at different speeds but that they werent aware of any adjustment?

Mazda's tolerance spec for compression is 120psi max and 98.6psi min at 250rpm
If my starter is only spinning at 200rpm... that will affect the compression numbers.
So we use a program to do all the math for us and figure out, based on our compression numbers, what it would be if it were spinning at 250rpm.
then we can compare those numbers to Mazda's spec.

And 273 is pretty high for a starter rpm... I've never seen one that high.
Is your starter aftermarket or the upgraded one?

I dunno I got it from a yard so it could be from a different year or something. I also have a larger battery than normal and I think that makes them spin faster. The guys above shows his cranked around the same.

So what does this convert over to:

115.70, 122.67, 119.91 @ 273rpm
122.67, 133.25, 128.61 @ 273rpm

I have the upgraded starter with a Redtop Optima battery and I've only seen 248rpm during a compression test.

I'm at work and have to download the conversion software... I'll let you know in a couple minutes unless someone beats me to it.

It converts to:
113.48, 120.72, 117.85 @ 250rpm
120.72, 131.72, 126.90 @ 250rpm

So whats your opinion on this - they told me at the numbers they gave me 125 and higher was considered high because of carbon build up.

That is true with piston engine... so I assume its the same with a Rotary.
Just to clarify... this test was performed on a warm engine... right?
You can also seafoam the engine and run it again to see how much the numbers change.

yea i guess - I drove it there and it took them alittle while to get after it but it should have still been warm.

the vacuum reading confirms it for me. Engine has wear.
What you may be able to do is to do to keep her going for a little while longer is do a deep decarboning, then use 1/2-1 oz premix/gal and switch to a 20/50W oil. That may help a little.

People do generally believe as that is what they have been educated to believe, that ambiet temp is what drives the choice of oil viscosity. While there is a little truth to that -it mostly centers around engine start up protection.
Think about it---does your engine temps run colder in a 40 degree day versus a 80 degree day? Nope --it doesnt--at least it should not.
In a sub 30F weather --no i wouldnt run 20w/50, I would run a deseil oil 15W/40
Anything above 40F I would run 20w/50. It all has to do with the oil film strenght and whether or not the oil can hold its viscosity.
Lot of good info in the forum about this.
Good luck dude and rotor on.
OD

^ Indeed OD Protection at engine startup is the most crucial element. Beyond that adequate viscosity for the operating regime, be that typical street (differing dependent on city or highway) or more rigorous track.

As we know basically the number to the left of the 'w' indicates the cold weather rating (lower being colder-ambient capable) and the number to the right the viscosity.

The bottom line is to select an oil based on your projection of climate and use for the next 3k miles.

Damn... out of curiosity what's the expected vacuum for a healthy 8?

I will definitely run seafoam/zoom cleaner and re-test. I will look into the oil more but the vast amount of info is counterproductive when trying to find the good information.

Oh Denny you were so nearly there! You are right on the money that your engine temperature and overall internal environment doesn't change regardless of what the ambient temperature is. Therefore, because oil is thickest when the motor is cold you want a viscosity at startup that is as close as possible to the viscosity of the oil when the motor is up to temperature. 20w/50 is like pushing honey through your motor.

Castrol GTX 20w/50 cSt @ 40 degrees C: 143.1, @ 100 C: 18 (Spread is 125 cSt)
Eneos 5w-40 (which I run now): cSt @ 40 degrees: 82.5; @ 100 degrees: 14.0 (spread is 69 cSt)


No, the "W" is an indication that the oil is a multi-viscosity oil. There is no winter rating for any oil.

Marc, if you need more information let me know and I'll take care of you.

Thanks Todd. I'm gonna run the Zoom Cleaner this weekend and throw in some new plugs, re-run the compression and vacuum tests and post up the results.

I may hit you up for some thoughts on oil though as I know how much time you've spent on this. I've been running RP 5w30 for the last 10000km (changed every 5) since I installed the OMP adapter. Temps here go from ~40 on a cold night to ~90-95 on a hot day, lower near the beginning and end of the season. I'm considering making the jump to 5w40 especially to help out on track days. I don't think the outdoor temps here will have a huge impact on the oil.

Be sure to run the zoom cleaner through the maint. ports on the lower intake manifold. That REALLY gets the job done. I recall Erick fabbed up a couple small vacuum lines with a T fitting which works pretty well.

Also, be sure to give the car a couple days before doing another compression test. While that stuff burns out pretty quickly you will want to give the motor time to get rid of any deposits that it dislodges.

As for oil, I ran the 5w-30 RP for about 40,000 miles and all the motors we have torn down running RP has perfect bearings. I've ran the 5w-40 Eneos since the formulation is a bit different and also I've got a lot of miles on the motor which means my clearances have loosened up a bit.