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Fellow enthusiasts and those much more experienced than I, it seems I can't solve my blow by issue and I'd love to get some good feedback and help as to why I continue to have issues. With an upcoming track day, I can't commit until I know my catch can setup works flawlessly without filling with oil in a 15 minute span of extreme hard driving. When I say extreme hard driving, I'm talking all out autocross level driving consistently past 7500rpm on some local twisty roads.
The problem - In 15 minutes of hard driving, my catch can fills with oil and begins leaking out the front filter.
Catch Can Setup - I have a racetronix catch can with -10 AN fittings and lines(see link for more info), thought to be large enough based on some other threads I've combed through. Hose is plumbed to the oil filler neck. Catch can located in cruise control module location(no longer have cruise control) which is as high as I can mount it in the engine bay.
Other mods that might be worth mentioning - Xcessive oil pan(has a top baffle), non sequential turbos @ 315whp, stock vacuum nipples on oil filler neck both capped, running Valvoline 20W-50 VR1 oil. The reason I mention these is, does the larger pan with a 6 QT. capacity contribute to more volume of oil being sloshed sideways to run up the oil filler neck? Is the 20W-50 oil too thick to drain back down out of the catch can lines, it cools in the lines, thickens and then doesn't drain, creates a clog and blow-by pushes it to can?
Do I need larger lines? Should I move the catch can nipple line to the top of the filler neck as oil may be accumulating in the flat portion of the filler neck? I should probably invest in a larger catch can but that won't fix the system flaw. Unless the flaw lies within the catch can baffling.
Any help, tips, things I'm doing wrong, fixes required are appreciated. THX!
I should think that the first step would be relocating the hose to the top of the oil filler neck and seeing if that helps.
A second problem may be sloppy engine clearances causing excessive blowby. I had a newly built motor that was constantly filling catch cans even on normal cruises. I broke that motor down and found that the builder was INCREDIBLY sloppy with the rebuild and seal clearances. When I rebuilt it properly with tight clearances there were no more blowby issues or overactive catch cans.
Thanks for the suggestion, I will be tapping the upper portion of the neck as soon as I can. I would like to think the motor has great clearances as it was built and street ported by a well known shop. I'm curious if a rich tune would contribute to an excessive amount of blow-by. That's another topic I'll be posting about soon but will save it for the correct section.
Dip stick does not pop out but it is a new oem dip stick so the rubber seals are better and tighter than the original.
I'm curious if a rich tune would contribute to an excessive amount of blow-by. That's another topic I'll be posting about soon but will save it for the correct section.
It wouldn't really contribute to blow-by by definition, but it would definitely result in the oil being diluted with fuel, and if the dilution is really excessive, the oil level in the sump will actually increase between oil changes. So yeah, under hard cornering & g-forces that you'd see on a track, an over filled sump would be more likely to puke liquid oil into your catch can.
It has a baffle in the neck to keep oil from working up and also it's pre-threaded for AN fittings.
A good catch can setup helps but if your motor isn't super tight (as stated by another poster) you just do what you can to help things out. A tighter motor will have less problems with blow by.
Whether or not you have excessive blow-by or too much oil in the sump, the higher on the filler neck that the nipple is located, the better. The body of the filler neck acts as a gravity-operated air/oil separator, so the nipple should be located as high on the neck as possible. That's how Mazda designed it.
You need to be scavenging the blow by from the sump. Easy solution.
I’m sure I’ve seen bumpstart post on here.
not sure if this is frowned upon but it’s valuable info.
You need to be scavenging the blow by from the sump. Easy solution.
I’m sure I’ve seen bumpstart post on here.
not sure if this is frowned upon but it’s valuable info.
I'm actually interested in the setups in that AusRotary thread, but those are absolutely the worst "drawings" and descriptions I've ever seen and I can't figure them out.
I'm actually interested in the setups in that AusRotary thread, but those are absolutely the worst "drawings" and descriptions I've ever seen and I can't figure them out.
haha. I agree.
keep it simple.
Vacuum line from air filter to filler neck so when you are in boost it is sucking the blow by from the sump.
That's what I'm curious about. "to vacuum" implies to the UIM as the factory does, but you're suggesting the turbo inlet (air filter). Reason I don't love that is, the air/oil isn't separated coming up that neck, so it could be that the reason it isn't filling the catch can is the turbo/motor is ingesting the oil blow-by.
I'm also surprised you get any "vaccum" effect even on boost, because the turbo has a MUCH larger opening through which to draw air (the filtered inlet), and there's a large filter on the catch can (ultimately connected to the same system).
Reiterating what ptrhahn said, hooking a vacuum line up to the blow by line anywhere pre filter defeats the purpose of the system. Also, I wasn't convinced with Aaron's video after watching, its obvious the reason his blowby oil accumulation disappeared, it is being put back into the intake tract and motor. Again, defeats the purpose. Yes, hooking a vacuum line up to the filler neck will equal the air pressures, especially if your lines aren't large enough. Any vacuum on the catch can (or positive pressure side) will only pull oil to the filter or intake(if PCV hooked up).
I am curious, is there any type of blowby occuring during high levels of engine vacuum, say when you're 0% throttle and braking or coasting from a high rpm?
Also, anything pre turbocharger, you'll always be in vacuum. But I think ptrhahn was implying vaccum even when in boost will just pull air from the catch can filter. It can get really complicated when it comes to pressure vs volume of line vs volume of air expelled with blow by versus vacuum.
I'm over thinking this, but, the PCV doesn't make sense with a catch can setup that has an air filter. A different story if there was no filter to atmosphere.
This all had me down the rabbit hole, and I think I may try an air/oil separator with drain to pan between the filler neck and the catch can. Depending on what shows up in the catch can after that, I might reduce the size of the catch can.
but it would definitely result in the oil being diluted with fuel, and if the dilution is really excessive, the oil level in the sump will actually increase between oil changes.
I am interested in this statement. We have gas in the oil, can tell by the smell.
We have not figured out yet how its getting there but have some ideas.
Our plan in the mean time was to change the oil when we smell gas.
But even after changing the oil, its still smells like gas.
So maybe this is the problem.
How do we get the gas out of the sump when changing the oil?
Fuel dillution is normal, and part of why we do such frequent oil changes. also why I run 20/50. It'll be even greater if you have decel fuel cut off. If it's excessive, i.e.; you're significantly filling the pan or the oil is super thinned out, you may have a problem, but just smelling like gas is pretty normal.
The primary turbo inlet (or just a turbo inlet on a single turbo) does not have a significant amount of vacuum. You need a restriction to create vacuum. The giant air filter keeps it from having any major vacuum. Air moves through that pipe, if you put a regular boost gauge on it you would barely see it move off the zero point. The ONLY place in the engine with vacuum is between the throttle plates and engine, that's it.
Stock there is a PCV valve (gray/black, about 8mm inlet/outlet) that goes from the oil fill neck to the upper intake manifold. Mazda got rid of it on the 95 cars. The 95 setup is just a line from the oil fill neck to the primary turbo inlet, that's it.
Fuel dilution is just going to happen on rotaries. You have the combustion chamber wet down with a rich fuel mixture, the oil control rings scrape the walls of the combustion chamber and pick this up as well as some blowing by worn or out-of-spec side seals into the oil in the center of the rotor. As stated, 20w50 oil and change regularly at 3000 miles and you are good.
Street cars typically have near no problems with PCV. I have a Jaz catch can and barely have much of anything to get excited about in it when I empty it during an oil change. Track cars are a whole different animal, there's been TONS written about track guys trying to keep oil out of the PCV system. Most of that is pulling VERY high G's (many times on race tires) for a long time - you simply can't replicate that amount of force on the street.
The primary turbo inlet (or just a turbo inlet on a single turbo) does not have a significant amount of vacuum. You need a restriction to create vacuum. The giant air filter keeps it from having any major vacuum. Air moves through that pipe, if you put a regular boost gauge on it you would barely see it move off the zero point. The ONLY place in the engine with vacuum is between the throttle plates and engine, that's it.
Stock there is a PCV valve (gray/black, about 8mm inlet/outlet) that goes from the oil fill neck to the upper intake manifold. Mazda got rid of it on the 95 cars. The 95 setup is just a line from the oil fill neck to the primary turbo inlet, that's it.
Fuel dilution is just going to happen on rotaries. You have the combustion chamber wet down with a rich fuel mixture, the oil control rings scrape the walls of the combustion chamber and pick this up as well as some blowing by worn or out-of-spec side seals into the oil in the center of the rotor. As stated, 20w50 oil and change regularly at 3000 miles and you are good.
Street cars typically have near no problems with PCV. I have a Jaz catch can and barely have much of anything to get excited about in it when I empty it during an oil change. Track cars are a whole different animal, there's been TONS written about track guys trying to keep oil out of the PCV system. Most of that is pulling VERY high G's (many times on race tires) for a long time - you simply can't replicate that amount of force on the street.
Dale
Dale,
All good points, especially on vacuum at the turbo inlet.
I'm actually very interested in the concept of "equalization" between oil pan and manifold as Aaron describes in the video. I had an issue recently where I'd plumbed the oil injection nozzles to a spare nipple on the filler neck (because there's a -10 AN line to a large (1 quart) filtered Jaz can there. I'd originally done it because frequently blowing oil jets sprayed oil all over my engine bay. But, with a new motor, it smoked (no more blown oil jets). Ultimately fixed by disconnecting that line and instead running to a small filter.
I now want to put a boost gauge on the filler neck, because A, I want to know what the heck was going on there, but B want to see if pressure is still built with that -10 line, maybe I need a -12, or if its just oil climbing the neck that tends to fill my catch can.
For recording intake pressure drop you need a gauge that can read in inches of water. That's smaller resolution than a typical vacuum gauge. You can get digital ones fairly cheaply off Amazon. It's considered a differential pressure gauge/manometer.
I now want to put a boost gauge on the filler neck, because A, I want to know what the heck was going on there, but B want to see if pressure is still built with that -10 line, maybe I need a -12, or if its just oil climbing the neck that tends to fill my catch can.
That is an excellent idea, I may steal it. I've been thinking about adding a catch can to my mostly-stock car that sees occasional autocrosses and track days, and it would be nice to have some before/after data aside from guesstimating the amount of oil that got into the intercooler. From what I've seen from piston cars, those guys are often using a couple of large breather lines. If our rotary engines are getting a lot of fuel in the oil, I suspect we might have more crankcase pressure than a similar-power turbocharged 4-cylinder engine.
After combing through some older threads in the Race Car section, I believe I've found the key to my problem and its a rather simple one. My issue lies in not venting both sides of oil pan. If you're going to be doing any hard driving where the car experiences high side to side lateral G's, venting both sides is a must. For single turbo cars, easy solutions include using the rear oil return to vent blowby pressure, or if you've removed the oil metering pump and blocked it off with a cover plate, you could also tap the plate and vent from that location. For those that are still using the twin turbos and the oil metering pump, I suppose tapping the oil pan is your next best bet. Anyone want to weigh in on the best spot to vent the cold side of the motor when the tt system and oil metering pump is in use?
On a side note, I'm not sure why but running 20w-50 with BNRs (and an open -10AN in an IRP Filler neck, also waiting on a good oil catch can solution) caused some weird pressure build up and oil to leak out of part of the turbo assembly. It wasn't internal as I never got any blue smoke through the exhaust, it just ended up on the hot housing and caused smoking in the engine bay.
I changed the oil back to 5w-30 and haven't ran into the issue since (it would happen even with the car just idling on 20w-50) even after WOT pulls.
Not sure if there's a direct cause and effect relationship with the oil weight but sure beat my worst case scenario of having to pull the turbos out and sending them back to BNR to be rebuilt again.
You can't really put a vent in the oil pan. When the pan is full the oil level is above the rail, if you tried to put a vent in it would be underneath the oil level and wouldn't properly vent.
09-11-21, 05:50 PM
