Blowing smoke on deceleration after boost
 

I drove my car for the first time today since finishing my turbo build, it is blowing a lot of white smoke on deceleration after a pull in boost. It also blows a small puff of smoke on shifts. I searched and cannot find a definitive solution. Help will be greatly appreciated!

Build Info
-NA8
-MS3x
-ID1000
-ARTech manifold, downpipe, and exhaust
-used SR20 turbo from zilvia (Garret 2560 journal bearing), no restrictor (see pictures below)
-turbo supply line = -4AN, turbo drain line = -10AN (see pictures below)
-OEM PCV with line to intake manifold on cold side of valve cover, vented to atmosphere on hot side of valve cover (I will be getting a catch can setup soon)

Main Points
-a lot of white oil smoke comes out of the tailpipe for a few seconds after a few seconds of pulling with boost (6psi max). No boost = no noticeable smoke on deceleration
-according to a friend, there is also a small puff of smoke on shifts with no boost
-no smoke during the pull
-no smoke when revving without load (I held a steady 3000RPM for well over 5 seconds in a parking lot while watching the tailpipe and there was no smoke at any point) Sometimes it smokes a lot when idling, other times it does not
-this car did not smoke, burn coolant, or burn oil before this build. I did not open the engine during the build
-turbo was bought used from zilvia, it does not have excessive shaft play and looks like it is in really good condition (but I still think this is a turbo problem in some way, maybe turbo drain?)
-there is no oil in the compressor inlet, there is no oil in the charge piping or intercooler, all of those areas are completely dry

Do I need a restrictor even though this is a journal bearing turbo? Does my oil drain line stay horizontal for too long? I am not sure where to go from here because from what I have read when other people (on this forum and others) post about similar issues, they always have more symptoms. They smoke during the pull, or while revving, or there is oil in the charge piping.

Pictures of my turbo's oil inlet and drain line. Any suggestions would be greatly appreciated!

Seals on the turbo ok? Turbo housing all good? I suopose if oil was getting into it the smoke would be blue-ish. Anyway my first thought was the turbo itself and its state of health

Seals on the turbo ok? Turbo housing all good? I suopose if oil was getting into it the smoke would be blue-ish. Anyway my first thought was the turbo itself and its state of health.

I bought the turbo used and did not take it apart before installing it, so it is possible that the seals are bad. If the seals were bad, wouldn't there be smoke all the time and during acceleration in boost (not just on deceleration after boost)?

I had almost the same problem when my headgasket was leaking. After boost pull when the RPM drops on its own without braking to a certain RPM lots a smoke. With normal driving not, only when boosting

Could very well be the restrictor. It is a must on Garrett turbos.

The only issue with that I see with headgasket is that I do not have any of the symptoms that generally come with headgasket failure.

Even on journal bearing turbos? Instinct tells me that it would be better to rule out everything else before restricting oil to the turbo.

Yup. Read about it. My T25 is journal and I use a restrictor. I searched around before buying and the Nissan guys said you need it.

According to Garret a restrictor is generally not needed on journal bearings turbos........

https://www.turbobygarrett.com/turbo...oil_restrictor

It later says it is a good practice for a non rebuilt journal turbo. Most are at least 20 years old by now. The nissan turbos were fitted with one from the factory and a 10$ part couldn't hurt.

That is what I found as well.

I am leaning towards piston ring blow-by in boost, then on deceleration when the intake manifold goes into vacuum the oily air in the now pressurized crankcase is sucked in to the combustion chamber and goes out the exhaust. I am going to check compression and do a leak down test. Any thoughts on that theory?

That is another part of the problem. I bought this turbo used and have no clue what it has been through. However, if it were turbo seals I would expect a couple of things:

1. I would expect to see smoke at times other than only when decelerating. There is literally no smoke at any time except for when I come off of the throttle after being on it.

2. I would expect to see oil at the compressor inlet, or in the charge piping, or in the exhaust. There is no oil at any of those locations. That makes me think the oil that is making it out the exhaust is oil vapor (as it would be if it had gone through the combustion chamber).

Overrun conditions can suck oil around the rings and where I generally see oil smoke first on tired engines.

I have 0 experience with this. How much smoke would you expect to see in a situation like mine (if it is rings)? After a sustained pull in boost (even at just a few psi), there is a period of 2-3 seconds where there is a lot of smoke. Like enough smoke that if it were coming from under the engine I would be confident that my car were on fire.

In my car I know for sure the rings are toast. I see big clouds of blue smoke and I have a quart of oil per 800 miles consumption.
Keep an eye on your oil consumption. If it's not a big deal I wouldn't give it a second thought.

I am going to try a few things, but if it does not stop I am going to drive it until it goes for real. Then it will be VVT time.

I had an old small block Chevy that was beyond wore out, as a trick I'd run it up to 6k RPM and then let it coast down to 4k. It would haze smoke doing this but when I'd jump back on the gas at 4k I could cover 4 lanes of highway in smoke thick enough you'd think I blew the motor.

Every motor is different, compression and leak down numbers will tell you how bad it is.

That's the Miataturbo.net spirit :)

I hope mine does not get to that point once I start turning the boost up!

I try!

What size restrictor do you run on your T25?

That motor had like .015" cylinder wall wear and would blow the PCV valve out of the valve cover from all the blow-by......Good times.

I bought mine from a local performance shop but I think there's only one size fits all:
t25 turbo oil restrictor eBay

That is impressive!

UPDATE: The smoke is worse and is now also happening pretty much all the time. Sometimes worse than others. The turbo is blowing oil past the seals for some reason. The image below is after running it hard. I think it may be turbo oil drain related. Could someone with more experience tell me if my oil drain line is horizontal for too long (second image)? https://cimg4.ibsrv.net/gimg/www.mia...98e5c7d260.jpg

https://cimg7.ibsrv.net/gimg/www.mia...43674fe8b1.jpg

Going back to the original post , " white smoke " says coolant not oil to me. I vote for head gasket. Fredb

I completely forgot to add in the update that the smoke is without a doubt oil smoke, not coolant smoke. Since it is now occasionally smoking at idle I am able to see the smoke without looking through the rearview mirror. While it is not the same blue that you would typically associate with oil smoke, I can smell it and know that it is smoke from burning oil.

I read somewhere that oil smoke that does not go through the combustion process (goes straight to the downpipe from the turbo) is not always blue. I think that is what is happening here. I am going to make a new drain line that does not go horizontal like my current line does. If that does not fix the problem I guess I will be looking at using a restrictor even though that is supposed to be a last resort type of thing for journal bearing turbos...

I took my oil drain line off because I am going to make a new one that does not go horizontal at any point. I found that the ID of the -AN line fitting is 3/8" even though it is a -10AN line. Does anyone know the standard ID of this fitting? I am using commercial lines on my car that may not be standard. Also, my drain line is a nylon braided line, not stainless, so I think the rubber may be thicker = smaller ID.

https://cimg6.ibsrv.net/gimg/www.mia...92020c7dea.jpg

UPDATE: I made a new -10AN oil drain line that does not go horizontal at any point, it still smokes blue a lot.

Next, I installed a pop rivet restrictor (takes the ~4mm fitting inlet and makes it 2mm), it still blows blue smoke like I converted it to run on engine oil.

I am buying a turbo rebuild kit now. I don't know what it could be besides turbo seals at this point...

You might try running out without the turbo on for a few seconds to see if it blows smoke before you spend money on the turbo. Just a few seconds of running will tell you what's up, I've wouldn't run it long like this.

Just let the manifold open in the engine bay? The only problem would be that I would need to drive it some to be sure that it's still smoking.

Yeah don't drive it, I would only idle with it pointed at the shock tower. With that much smoke I betcha you'll be able to tell if it's pre or post turbo on disassemble.

That's a good point. Dry manifold and wet turbo would mean turbo problem and not engine problem. Based on what I've tried so far, do you think I can confidently say I've narrowed it down to either an engine issue or turbo seals?

I would think so, that's about the only way to get oil smoke.

I know this has been beat to death at this point, but I would like to add a little experience story.

I boosted my Honda insight that had 300k miles on the original motor/trans. It smoked like a chimney from day one, I assumed it was the Ebay GT12 that just had bad seals, because the car never smoked before, so I just kept driving it. 50k Miles later my hybrid battery died on the car (unrelated to the turbo) so I decided to give the entire system away to a friend who I owed money. Guess what? He put it on his car and it only smoked while the old oil burned off. Since then, it has never smoked.

Thank you for all of your help on this!


Thank you for the insight. I really hope this isn't an engine issue. I have a hard time accepting that it's an engine issue because it did not smoke or burn any oil before this build. Also, even when I only run 2 or 3 psi, it still smokes just as badly as it does at 10. That makes me think the smoke is proportional to oil pressure (RPM) and not boost. Which suggests a turbo issue to me.

Honestly at this point I'm just hoping I do not have to pull the engine again. Because if I have to rebuild it then I am going to build it for real which will mean a lot more money and time.

The manifold is dry. I have not gotten the downpipe off yet, but I am hoping from the downpipe it is obvious that there is oil post-turbo but no pre-turbo.

Well, when I pulled the turbo off, the engine no longer smoked. So... Yea.

Wait so the engine did not smoke before or after the turbo was on but it did smoke with the turbo? Then your friend used the same turbo and it did not smoke?

I had a similar issue that progressed like yours(first just smoking when getting off throttle then started always smoking after a few hundred miles). I checked everything, oil restrictor, oil drain, etc. The telling sign was that smoke/oil started coming out of the crank vents due to a bad cylinder and had so much pressure you could see pulses of air oil coming out the vent filter. I did not see if you said you checked compression but that was the final indicator. Mine was 3 cylinders where in the 160psi range and cyl 3 was well below 100psi.

I have not checked compression or done a leak down test yet. I do need to get that done though. I will report back here once I find the problem.

did you end up fixing the issue?