Which hose comes from the oil filler neck?
 

Which hose comes from the oil filler neck? I am in the process of installing a catch can and I can't trace the hard line from the filler neck down to the inlet elbow. The idea is filler neck to catch can, then catch can to inlet elbow.

Also, the primary turbo intake hose has oil in it but the secondary turbo intake hose does not. The car has been overfilled with oil in the past and I'm guessing the oil is coming from the oil filler neck to inlet line? Or do you think it could possibly be coming from the oil injectors?

Thanks.

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The one on the right. Put the catch can in line with that hose or cap it all together and run the catch can line to the bottom port of the oil neck. Make sure you eliminate and cap the pcv.

The oil in the primary inlet would most likely be from the overfilling, seeing as it is only in the primary. I doubt it would have anything to do with the oil injectors.

The oil is probably only in the primary Inlet because that is where the crankcase blowby vents into when you are boosting.

Or, filler neck to catch can, then catch can to hose that used to connect to filler neck

i.e. you don't have to run a hose from the catch can to the primary turbo inlet elbow since there is already a line that's there which is hooked onto your filler neck. Just take that hose (which was attached to the filler neck) and connect that to the catch can

The primary turbo inlet tends to get oil there because the stupid stock breather system dumps it there. Putting a catch can should help.

I just did what you are doing now, last week.

1. I removed the PCV line going from the oil filler neck to intake manifold. Capped the now spare port on the oil filler neck. And capped the now spare port on the UIM. This is because the PCV is not required and 1995+ cars don't have it from the factory. Its just another potential boost leak.

2. I bought a sealed catch can with two 5/16" hose port barbs on it. And a drain plug on the bottom.

3. I cut into the line that goes from the oil filler neck, down to the turbo inlet elbow. I spliced the catch can into that line simply as follows:

Line from Oil filler neck goes into catch can.

Line out of catch can continues down to turbo inlet elbow.

This system is sealed. Which is very good.

The turbo inlet elbow pulls constant vacuum from the crankcase, and the catch can is inline to catch any oil before it goes into the turbo inlet. I've driven it in anger for 1 week so far and it is working great with zero issues. I highly recommend it.

Yes, I thought about that overnight and it might be a lot easier to simply plumb the catch can back into the hard line near the filler neck that already goes down and connects to the primary inlet elbow, it would just potentially look a bit unsightly.

I am going to be running a Saikou Michi S3-OCC baffled catch can which is pretty large and was test fitting hose routes last night down to the inlet elbow.

I am using 3/8" hose though as I was told nearest to 9mm was the correct size to directly connect to the filler neck and inlet elbow? I have hose clamps which I can use to tighten things down just in case.

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Instead of routing the hose down here

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Route to here?

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Any reason why you chose a sealed catch can setup? I prefer a vented catch can. There is actually little to no vacuum generated at the turbo inlet. Air is going to take the path of lest resistance and it will pull front the filter. The reason the crank case vent is plumbed into the turbo inlet is so any oil goes back into the motor and burnt.

Huh, are you sure about that? How does air get to the engine if it's not pulling it from the intake, via the primary turbo inlet.

I ran an unvented catch can and would have to drain it after every track session, about a pint. Part of the problem may be the oil level, which maybe high if you fill it to full.

A sealed system is more efficient and a baffled one is the best given that it doesn't allow gunk to continue through to the inlet elbow. Also, the sealed system won't result in an accidental mess of oil in the engine bay (not that I expect to ever have that scenario).

Are you sure the inlet elbow doesn't create vacuum or a suction effect, particularly under boost when the turbo is spinning at a crazy speed and drawing in air? I thought that was the point of using the inlet elbow as opposed to the intake manifold because the suction from the turbo creates a vacuum effect whilst the intake manifold would be creating positive pressure when under boost.

A quote from a Supra forum below.

"A functional PCV system is even more critical to turbocharged engines. Turbocharged engines generate crankcase pressures far above those experienced by a stock motor. Simply attaching a filter to the PCV valve will not cut it. The factory PCV system simply isn't up to the task, and unable to keep up, excessive crankcase pressure will result, causing poor piston sealing, blowby, intake charge contamination (which in turn introduces detonation), and ultimately ring damage. And because the PCV system relies on a vacuum source to operate, it will not function when the engine is under boost. This is because like the whole intake system on a turbocharged engine, it is pressurized when under boost. And since the PCV system is sourced by a vacuum source on the intake manifold....Well, you get the picture. But this is precisely when a PCV system is needed the most. One must find a means to evacuate excess crankcase pressure, which builds exponentially under boost and heavy load. This is where a air pump comes in. By using an air pump you introduce a vacuum to the crankcase. This will evacuate the crankcase gases at a much faster rate and help the piston rings to do their job. With very little crankcase pressure to fight, engine builders car run looser tolerances. With looser tolerances comes less friction and reduced parasitic drag."

Anyway, with respect to my photo above, I'm assuming I can run both lines in the following ways:

1. Filler neck to catch can to hard line near filler neck which connects to the primary inlet elbow.

2. Hard line down near primary inlet elbow that originally comes from near the filler neck to catch can to primary inlet elbow.

3. Filler neck to catch can to primary inlet elbow, therefore leaving a redundant hard line in place that won't be used.

I don't think that's technically correct, as the stock rats nest uses vacuum to operate its myriad solenoids and chambers... And its main system vacuum source is the second barb on the turbo inlet elbow...

Mazda chose to route the main vacuum for the rats nest and the oil vapor system off the turbo inlet as there is always significant vacuum there, under manifold boost or idle. Enough to supply an entire solenoid system to operate correctly.

The turbo inlet can only provide a source of filtered air and not a real source of vacuum.

think about it. the vacuum needs to be pulling from the far end of the tube..
You cant go attach a hose to the intake and expect it to pull vacuum at the other end. It needs to pull from the other end to start with..if that makes sense

https://cimg7.ibsrv.net/gimg/www.rx7...ea3f6d975e.jpg

Well if that's the case, where/how does the rats nest get initial significant vacuum signal from?

I know it does store some vacuum in the small reservoir plastic tanks, but they need to source it from somewhere.

The vacuum diagram (and other documentation I've seen, unless its wrong) shows/says that initial vacuum comes from the turbo inlet elbow. This is why there are two barbs on the elbow- one draws crankcase vapor and the other barb goes up to a "vacuum manifold" which supplies the turbo precontrol solenoids... Now surely if Mazda wanted reliable operation of the precontrol solenoids, they would have made sure that running them off a small log manifold that only gets its vacuum from the turbo inlet elbow, was going to be a good reliable source of vacuum?

There is another small line off the front side of the UIM with a check valve in it, which goes to the rats nest. Presumably this also gives manifold vacuum to the rats nest when the engine has vacuum in the UIM (not sure, can't trace it well), but it would fail to supply vacuum during boost.
The inlet elbow appears for all intents & purposes to supply vacuum.

which hose in this diagram are we talking about?
https://cimg8.ibsrv.net/gimg/www.rx7...24e3c4dde6.jpg

Dark Blue, Dark Green and light pink.
I think the RX7 gets it's main source of vacuum from the UIM, if you follow the green from the vac chamber to the UIM.
Now I could be wrong on this but I don't think there would be a significant amount of vacuum from the primary elbow because in order to create vacuum there would have to be a fair amount of restriction from the air filter which would rob HP, but once your past the butterflies in the TB then there would be vacuum until you start building boost which is where the vac chamber comes into play.
The tube on the primary would have a slight vac but nothing to write home about, unless the air filter is plugged. There might be a venturi effect? but that is just speculation.

Mike

So, here is the route from the oil filler neck to the catch can. I took off the old cap from the top nipple on the filler neck and used the cap to plug the bottom nipple that was connecting to the hard line down to the primary inlet elbow. Unfortunately, I couldn't take the old hose out due to lack of room to maneuver so just left it there unconnected. I will need to sort that out at some point for aesthetic reasons.

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Next, is my connection to the primary turbo inlet elbow highlighted by the hose clamp. Did I do this right? Also, I need to get a new hose for the left rubber hose as it's hard as a rock and really easy to take off from both sides.

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Current routing from inlet elbow back to catch can, but will probably move it from between the master cylinder hard lines where it sits now. Was just trying to "stealth" the piping.

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Please let me know if I did anything wrong.

The solenoid rack gets its vacuum source from the green hose going to the uim with the check valve.

100% wrong.

One line to the primary intake elbow is for the PCV from the oil filler neck. The other goes to the OMP nozzles. The vacuum chamber is charged through a vacuum line with a check valve inline from the UIM behind the throttle body. The pressure chamber is charged from boost at the Y pipe with a check valve in line.

The purpose of plumbing those connections to the intake elbow is for filtered air; not vacuum. The PCV sees vacuum from the line from the filler neck to the UIM. I'm not rocket math magician so I couldn't tell you mazda's reasoning behind eliminating the line in 1995.
Matt

so how come the UIM is pulling vacuum and the intake is not????

The UIM is pulling vacuum because the engine is creating vacuum but the butterflies in the throttle body are restricting flow. Any source before the butterflies would have minimal vacuum where after the butterflies there is significant vac while at idle or light throttle application.
you can check this out easily if you have a boost gauge that also reads vac by just moving the boost/vac hose from the gauge to one of the nipples on the dark blue manifold.

Correct. The stock PCV setup has two points of vacuum from the oil filler neck, the primary turbo and the UIM (via the PCV). Problem is under boost, the PCV is closed and the primary turbo is sucking in a good amount of air which is pulling good vacuum to the oil filler neck and thus pulls all the nasty vapors and possibly oil (during hard cornering) into the primary turbo inlet which then ends up in the IC, hence the need for a catch can. At idle, when the butterflies are closed, there's probably not much vacuum from the primary turbo, but then again, there's not much vacuum (i.e. your not pulling gunk from the filler neck)

Agreed. So, is my routing in the photos above correct and ok?

Looks good (hard to see exactly though). Looks like you have the bottom inlet on your catch can routed to the primary turbo, which is your vacuum, and the top being fed from the filler neck

Ok, so I hooked everything back up and noticed no leaks when idling. Then, I went for a 15 mile round trip drive stopping at Shell in between to fill up. On this drive I drove pretty gently but made sure to hit at least 8 psi up to 5,000 RPM (limited by a 40 mph speed limit and speed cameras) just to build some pressure and see if anything started leaking. It's also important to note that right now the engine oil level is full and I know it should be at about 2/3-3/4 full to prevent so much blowby under boost.

When I got back I popped the hood as the engine was idling and looked at the filler neck and noticed that the bottom nipple which I capped off and faces downward is leaking a bit of oil as you can see in the following photo. The cap on the bottom nipple used to be on the PCV nipple which the catch can hose is now attached to.

I suspected that this might happen due to gravity but is there any way I can seal the bottom nipple better? Will a ziptie suffice? What about locktite?

What would you do to resolve the slow leak (and potentially a bigger one when I go to the track on Saturday and I am constantly in boost and high RPM.

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