Rb25det Blowing Smoke

[slowpoke2006]

So a quick description of the car and motor. It's an S1 Rb25det swapped into an 89 240sx with a FMIC, Freddy intake, an OBX bov stock turbo, stock ecu and wiring specialist harness. Its on its 3rd oil change running Mobile 1 fully synthetic advance formula 10w30. It has an oil catch can also. I didn't put the motor in the car i have just been going through every part of it and checking everything out that i can. It had a new water and oil pump installed before putting it into the car. when i got the car i changed to oil, plugs and cleaned the filter and checked the coolant. I have been driving it about for 3 weeks at 7psi of boost and some times 10psi set with a home made manual boost controller. The other night i get in the car after work and crank it up and let it warm up before taking off and it starts to pore out white/grayish smoke out the exhaust. Im setting at a red light when i notice it. Im around a few other cars so i pull into a parts store and let it idle there and i can see it just rolling out and it smelled like burning oil no sweet smell but would burn the hell out of your eyes. It would almost white out the car beside me. All my temps are good and it has great oil pressure. I limp it home. I couldn't tell if it was still rolling out while cruising home only when i stopped at a red light could i see it. I have done a block test to check for exhaust gases in the coolant system there was none, i have done a compression test and all 6 cyl are at 150psi. I went and got a cylinder leak down tester and tested all 6 cyl and they where all in the green with less than a 20% leak down. I did the compression test with the motor close to operating temps and didn't add any oil to the cyl. After putting everything back together its no longer smoking at all. It does have a slight miss at idle but that is being caused by my coil packs you can see them arc to the valve covers when it misses. Any ideas on what could have caused the smoke then it just stop the next day? Also i think my brake booster is going bad some times i have a great peddle and other times its hard a hell to mash so that is on the list of things to fix as well.

Thanks for any help.

James

[WMDC35]

Is there brake fluid in the vac line off the booster?

[slowpoke2006]

None that i could tell. The hose is dry.

[GTSBoy]

Most likely the turbo letting some oil into the exhaust then.

[slowpoke2006]

I don't know i have never owned a turbo car, but every time i have seen that on a na car it has been bad news. How bad would that be? Should i start saving for a new turbo or is it not a huge deal?

[GTSBoy]

Stock turbo is not rebuildable, so you're looking at a 2nd hand replacement or a highflow job or an outright brand new one.

But I would take it to a mechanic to get it diagnosed because leaping to conclusions based on internet diagnosis is not so smart. It could be leaky stem seals in the head or it could be oil control rings. Keep in mind it is possible to have high compression AND burn oil coming past the oil rings..

[Ryno]

Another thing to keep in mind is you are running quite thin oil (30 hot weight). For years I used 10W40 as that was recommended for the engine, but always suffered oil misting out of the cam shaft seals (with multiple seal replacements over the years (and different catch can setups) to try and solve the problem. I went to 10W50 oil and that pretty much fixed the problem.

Oil technology is getting pretty awesome these days... I now use Hi Tech 10W60 fully synthetic oil. So it has the same cold viscosity as your 10W30, but does't thin out so much when hot.

I'm not saying that the thin oil is definitely the cause of the amount of blow by you have experienced, but it may be a factor.

[slowpoke2006]

I'd rather not take it to a mechanic. How would they tell if it's the oil seals? A boar scoop or pulling the Pistons out and checking them? It hasn't done it again sense Friday night. As far as oil pressure when it's cold and I crank it up it has 80 psi. As it warms up it will drop to about 18 when fully warm and idling around 850. And as I Rev with it warm it will go back up to 80 psi at about 6500 rpms. I don't mind buying any tools that I would need to diagnose any of the problems.

Edited December 21, 2015 by slowpoke2006

[GTSBoy]

Your oil pressure has nothing to do with any of this. The fact that it sounds perfectly healthy is just something to keep you warm at night.

If by "oil seals" you are talking about the piston oil control rings that I mentioned.....no, of course you cannot inspect them from outside the engine. But here's the reason to take a car that is blowing smoke to a mechanic. These guys know what to do, in what order to cross off various options for oil burning from the list of possibles. You would appear not to. Therefore the mechanic is the better choice. It would of course be a waste of time taking it to a mechanic if it is not currently smoking. So if you did something to it that stopped it smoking, pat yourself on the back, but give up on trying to work out what you did because it would appear to be something random.

I am working on the assumption that it will start smoking again in the near future. A survey of threads like this one on this forum will show a pattern like this....

OP: I have a problem.

Replies: Several ideas for what it could be.

OP: I didn't do any of the things you suggested, but I have done several other random things, and now the problem has gone away.

Replies: <Shrugs>

Several weeks pass.

OP: The problem is back, worse than ever.

Replies: <crickets>, <indifference>

[slowpoke2006]

I know I didn't do anything that could have stopped it from smoking. I just did several checks to see if I had a blown head gasket. I can rule out blow by from the valve covers as they go to a catch can and not the intake. The other places that oil can get in are at the valve stem seals but you would mostly see it smoke on start up after its been sitting for a little while then there would be the turbo oil seals but I have no oil in my intake. I take care when checking things to make sure I'm not changing anything.The fact that it did it once means that something is going out. I'm just trying to rule out things that can be checked before I replace anything or start pulling the motor apart to check things. I'm not leaping to an conclusions. I'm looking to do test and find out the facts.

[GTSBoy]

Turbo oil seals don't just leak into the intake....... There are 2 sides to a turbo.

Valve stem seals can leak on overrun because the vacuum inside the engine will pull oil through.

Having someone who REALLY knows what they are doing actually SEE the smoke WHEN it happens is the best way to diagnose this stuff.

[AngryRB]

+1 for valve stem seals , how do the old plugs look?

Edited December 22, 2015 by AngryRB

[slowpoke2006]

They looked great. A nice tan brown on the tips and some black around the base at the end the the threads just suit that could be wiped off.

[AngryRB]

There pretty old motors, i'd try some thicker oil as said already, after that its valve guides, turbo etc.... the usual routine really.. later its blown ring landings etc etc

Edited December 23, 2015 by AngryRB

[slowpoke2006]

I think I may have found out what caused it the two lines going to my catch can are crushed flat so I think it was the crank case becoming presherised than pushing oil past the rings. But will also check into thicker oil. Will replace the lines to my catch can until then I connected them back to the intake

[Ca180]

Make sure it's decent lines i use hydraulic return hose for my set ups oil eats heater hose hard out.

I've had oil burning issues in the past my list is

Check plugs determine if oils being burnt through engine or just exhaust

Compression test

Leak down

Tear down

Swear words

Glad you got to a couple bad lines before it got really bad nice easy fix this time!

Edited December 23, 2015 by Ca180

[slowpoke2006]

I will be getting good hoses for it and will be watching it for the next few weeks and at my next oil change I will go with a little thicker oil like what was mitioned. I'm fixing my truck so I have something to daily if need be. New valves and rocker arms for it as the last owner didn't take care of it and it has smashed 2 valves on the exaust side. So 4 new valves and 4 new rocker arms with a valve lap job. Parts should be here today for that job. Guess I'll have a fun Christmas doing that job.

[GTSBoy]

These rockers are on the truck, yes? We're not talking about the RB any more?

[Ca180]

I'd be worried if we were.

[slowpoke2006]

I still am and will keep a close eye on it. I have checked everything I can with out pulling parts of the motor apart to check things. I will pull the turbo this holiday weekend after I fix the ka24e motor to check it for signs of leaking, but there was no oil on the o2 sensor but will check parts of the exhaust for oil. Not much else I can do with it not smoking ant more. I do think it could have been the clasped hoses th the catch can since that was the only place the motor could vent the crank case pressure. When or if it starts to smoke again is when I'll be able to check it out better and determine exactly is the cause. If at that point it's the Pistons oil rings then I'll pull the motor and rebuild it.