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Oil Consumption/Blowby in Fast, Sweeping, and Sharp Turns
Has anyone encountered excessive amounts of oil smoke on entering a higher than normal G turn? I'm actually surprised I haven't found a thread or post in track focused threads, though I did find ones relating to overfilling the oil. And I think my issue's symptoms are different, given that it's only happening right after a long sweeper or quick, sharp turns and not on straightaways.
I've got an on-ramp on my way to work that does a left hand 270° turn to merge with a highway, and whenever I'm pushing the car, upon acceleration out of the turn, I get a magnificent smoke show regardless of RPM band. The first time it happened, I thought a seal had failed or something and immediately pulled the car over and had it towed. Then it happened consistently (albeit somewhat less drastic) at an autocross event, where accelerating hard after making sharp turns would produce a nice cloud out of the tail pipe. My previous worn engine would have blow-by if I accelerated hard going in a straight line and didn't correlate to turns, but a straightline only hard acceleration hasn't happened yet with my current one. It's only happening under conditions that would cause oil sloshing or pooling to one side.
I bought a catch can yet to be installed, and I'm going to try running the car with the oil level a tick mark or two lower than full. I figure those two things done independently should confirm my suspicion that: 1.) The oil is entering through the breather tube line and not somewhere else, and 2.) that the pooling or sloshing must somehow block a pressure escape and results in oil reaching the breather tube.
In case anyone wants to throw out other suggestions, I'll mention my compression is okay, about 105 average ± 3 psi per rotor face, and it's been roughly 7500 miles since the rebuild. I have a Sohn adapter with Idemitsu, an AEM intake, working order intake valves, and a UIM from an 04, though mine is an 07. I'm using 5W-40. As far as I know, the rest of the oil system is stock.
LH turn would be away from the breather galley on the center iron, but if you pull the accordion tube at the TB then here should be signs of oil entering from hose at the oil cap breather tube connection if it’s from there. if not then the catch can won’t help. Never had that happen even with oil sump over-fill. I’d suspect it to be something else, but please confirm. Maybe block/remove the Sohn and try to see if it stops because I never ran one of those either (and won’t).
The ‘07 UIM has the additional PCV breather point added to it for the milky oil substance TSB issue, but mine is an ‘05 and never did that. If it is coming from the sump then the next step is to determine why. Because that would have to mean excessive blow-by when cornering, which again is not normal with an engine with good seals. It may be a rotor oil seal issue, though I’m not sure how that would manifest itself when cornering.
The oil fill breather tube runs right into the LIM ports on mine. The catch can should intercept the liquid oil from the vapors going to the LIM. I shouldn't have the additional PCV point since I'm using the 04 UIM, and I know for sure when I had the original 07 UIM, it was capped because of the AEM intake / VFAD delete. I only have 2 hoses running from the "accordion tube", the third is capped.
I'll verify there's no oil at the TB, but I've never seen evidence of it being there (as there's no hose for oil to get there). I couldn't think of a reason the Sohn would/could ever produce oil enough to cause this condition, but I'll try running it dry and see what happens. The first time this smoke show happened, the dealership the car got towed to diagnosed the plugs as fouled, which I thought could have been from too much 2-stroke (Sohn and was supplementing with mixed gas). But that doesn't explain why it would only do it on cornering.
I appreciate the pointers. I'll see if I can rig up a way to video, as I'm convinced the smoke is oil smoke, but I'm also slightly colorblind...
ahh, that was part of the ‘07 UIM breather configuration.
Without that UIM, then that hose assembly should also be deleted with the nipples capped just like the earlier vehicles. That’s likely to be the issue then.
Either that or the later UIM needs to be installed. I don’t think that hose to the LIM nipples is going to function properly without the other breather port and hose that was added where the UIM (not actually the UIM, but the PCV oil galley and intake valve vacuum tank assembly that bolts to the UIM) bolts to the center iron breather assembly. That’s what was different between the earlier and later S1 UIM.
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Early S1 PCV-vacuum tank on the left, later one on the right; note the large breather hose coming off at the lower RH corner and turning 180*. This is the new breather port & hose that was added in addition to other hose going to the nipples on the LIM.
just for the record, most of the mileage on my car is from street use and to say 99% of RX8 owners had this problem and benefited from this change is just more forum lore not borne out in either truth or factual data …
so what defines most people who have this issue? Living in a cold climate area with high moisture and/or not getting the engine oil temperature high/long enough to burn off moisture from the atmosphere that might accumulate in either the engine sump and/or oil fill/pcv chamber on the UIM.
There are a lot more than 1% of RX8 owners who live in warm or hot climate that didn’t ever have this problem. If anything they were fighting too high of oil and coolant temperatures.
I know no one wants to discuss this topic further, but if anyone has the patience to explain, I'm still having a hard time trying to understand exactly how the PCV system is supposed to work. Or maybe I do and it's not clicking.
Here's what I've put together. At a basic level, the oil fill neck (or PCV vacuum tank) just funnels oil to the oil pan. It's got one or two ports (depending on model year) built into it to allow for ventilation of oil vapor and condensation. These ports are under vacuum, but not enough that it could pull oil up like a siphon (right?). Supposedly it's strong enough to draw unwanted vapors, but in order for it to do that, there has to be a flow path. It can't just pull on the air mass in the tank and evacuate the gasses inside. Like sucking on glass bottle, you can generate a vacuum, but nothing is flowing. So does that mean there's air/gas that's being provided somewhere in the oil pan? Is there always a miniscule amount of blow-by present that keeps the gasses moving? It is called Positive Crankcase Ventilation, indicating there is always some positive pressure coming from blow-by. So does a healthy rotary not have ANY blow-by, or maybe a miniscule acceptable level? At higher RPM, you'd expect more blow-by than at low RPM, so does that mean there's more airflow through the PCV system at higher RPM?
I'm not seeing how our PCV system is necessary, if, by design, blow-by shouldn't be happening.
As for diagnosing my issue, here's what I'm thinking. Liquid oil should stay in the pan, and should never get past the bottom flange that connects the oil fill vacuum tank to the engine's mating flange, even under high G turns. Sloshing I suppose could get droplets up there, but unless the car was upside down, I can't imagine oil being able to flow all the way up to that point even under high speed cornering. Like Team has mentioned, he's undergone high G turns with an overfilled oil system, and not had oil reach his PCV port. You'd have to seriously overfill your oil to the point it's flowing out of the dipstick tube to get it in the oil fill neck under a high G turn. In other words, if the car was put on a G-force simulator without the engine running, you'd have to pull some insane G's to get the oil to overcome gravity and get up to the PCV oil fill chamber. Does anyone know if this is true?
So, if I have a catch can full of oil, oil is either being drawn up by intake vacuum, pushed up by blow-by positive pressure, or a combination of both unless I vent the catch can and don't have it recirculated. In the latter case, it would have to be positive pressure pushing the oil up, indicating bad blow-by. Does this sound right?
So regardless if I have one or two PCV ports, if I vent the catch can to atmosphere with just the oil fill neck tube connected, and STILL end up with lots of liquid oil inside, I should assume bad blow-by is occurring. I should also get rid of the idea in my head that it's the intake vacuum pulling oil through the PCV system because under a tight turn, the oil that's made it somewhat up the filling canal has blocked whatever normal flow path the gasses take.
As an update to anyone viewing this thread, I believe my original issue has been "mitigated". I take the same way to work M-F every week, so there have been plenty of right sweeper possibilities for it to happen. I'm fairly certain this was an issue relating to pressure, and here's why.
When I did my next oil change, I made sure to not fill past the full mark (which I typically overshoot by about 1/8th of an inch on the dipstick). Still had a smoke show event on a sharper on-ramp that it happened on, not my usual commute one. So I concluded it's not overfilling the oil that's causing it. So I threw in a catch can with a breather filter, and capped the LIM ports. Since then, there's been no incidents. I haven't done any autox events with it installed yet, but a month of commuting and taking the same on-ramp sweeper has yet to even deposit oil into the can. So the next test is finding an empty road or parking lot, and giving the car a proper shakedown. I'm convinced now that exhaust gas was finding a way into the oil system, and having the breather filter alleviates that pressure constantly without oil consumption. I know my engine isn't in perfect condition as it's a rebuild with average compression (little over 100psi on all faces), so blowby is bound to happen.
I plan to install an oil filler tank with the 2nd PCV port once I get some time and get it painted to make the bay look pretty. I'm going to try to tee that line into the catch can too and see what happens, though I don't think it'll make a difference as nothing will be under vacuum still. After that, I'm thinking I'll try swapping the breather filter for a line back to the LIM ports (or one of the three intake ports), and see if that draws any oil into the can. If it does, and swapping back to the filter doesn't, that should jive with my theory that it's a combination of positive "crankcase" pressure and intake vacuum that draws oil up and causes the smoke show events for me.
06-02-2021, 11:48 AM
