This post regards my 1992 camaro rs (305 tbi). So as I have been looking into this car more and taking it out I have realized that the driver side pcv valve is loose and the grommet looks like ****. My mechanic said the engine had some blow by and it’ll get to be an oil burner. The problem is that on a ride out last night every red light was a slight smoke show from my engine bay. When we got to where we were going we found out the pcv valve wasn’t in the grommet. So my problem now is if I replace the grommet, and valve along with relocate the line so it has less tension on it, is it a bad thing. Because clearly pressure is somewhere in the engine and if I do this am I making it worse? Idk please help

 

There is always gonna be a bit of blowby, NO piston to cylinder fit can ever be 100% sealed because then the piston would be too tight to move.

Fix the issues you mention and the smoke should go away.

And speaking of go away, if your gonna own a car of this vintage and you aren't a millionaire, it's time for this "Mechanic" creature you mentioned to go away and for you to learn to maintain your car yourself. No one says ya gotta start out by rebuilding your engine, but learning how to do simple tune up stuff like maintaining your PCV system will start you on your way toward saving mad $$$ . Learning and understanding how your car's various systems operate and interrelate will make you a more informed owner, and less reliant on people whose help usually costs upwards of $100 per hour.....

 

Compression checking all cylinders is a fun test if you wish to learn your car. So is degreasing things and seeing if there are external oil leaks you can find.

Do the valve guide seals if it's "using" oil. Very common on higher mileage third gen engines.

If there's tension on the PCV hose, maybe lengthen it instead of relocate.

 

yea I get that, I’ve done a lot of work to it myself but this is something that as a young kid with his first car I don’t know what is next. The family friend who just so happens to be a mechanic told us about the blow by so that we knew it wasn’t perfect.

 

What's the mileage? My 1986 C4 Corvette that I got with 90k had some blow-by, switched to 10w40 and it improved a lot.

 

it has 140k.. I’m on stock recommended oil I believe is 10w-30

 

You should likely run some quality 10w40 in it. I always ran 5w40 synthetic in my higher mileage 305 and it helped with consumption.

Watch your oil pressure - it will probably go up a bit with the 40. My 305 was always about 35 psi at a hot idle with 5w40.

GD

 

Maybe you can measure the blow-by , flow rate is easily calculated,



estimate using temperature and air density near ambient to satisfy that equation after setting up the pcv system as I describe here:
https://www.corvetteforum.com/forums...post1603290397

The question is whether the amount of blow by you are experiencing is more than typical or more than it should be.
The answer lies in being able to tell from experience or from using math.
I could tell you by standing there but you can make comparisons with other engines (from a toyota or whatever) by measuring flow rate using math.
Hooking up PCV will reduce the blow-by, but that doesn't mean the rings and cylinder walls aren't shot and blowing by extra sauce.

 

A oil catch can inline with your PCV system can help reduce the amount of oil that is allowed into the intake manifold.

 

You would think so but, actually this is a terrible solution, as it creates many more problems.

The best solution is to shorten the line leading from crankcase to intake manifold as short as possible, like an OEM line, using a small diameter hose, like OEM size hose.
Fast, hot moving crankcase vapors act as detergents because oil and gasoline can both become cleaning agents as long as they are hot and moving rapidly, which they are fresh out of the crankcase.

The last thing you want is to slow them down, that is why they can collect and clog up lines. For example if you install a very long long hose between intake and crankcase the hose itself will become a catch can, as the vapors cool and slow they will stick to the hose inner diameter, they settle out as sediments and brown/black carbon sticky tar-like substances and as they collect they will draw more of the same to themselves, gradually clogging the line as those carbon deposits stick to every surface when they are allowed to cool down.

Why else is a catch can a terrible idea?
The additional volume of any catch can or large hoses will reduce PCV signal. Similar to installing an intercooler between the turbo and engine, you have created a pressure drop due to additional volume, even if we neglect the resistance to flow the intercooler causes (like the resistance a catch can creates, which can be neglected here)
While a turbo can reference intake manifold pressure and compensate for the pressure drop, a PCV system has no such reference, so overall the flow will decrease. In other words it will hinder PCV suction, it will reduce PCV performance if the orifice and flow rate is not adjusted to suite the new additional volume of added lines and catch can. And this is a bad idea because increasing PCV flow rate means that any accidental clogging of the fresh air inlet side of the crankcase now can more easily damage engine seals and the oil pump. In other words, it is ideal to keep PCV flow rate as low as possible, that is, only as high as necessary, to achieve the required pressure drop of 1 to 3" Hg in the crankcase at all times.

 

So all engines will have blow by, the higher the mileage and wear the more the piston rings will allow through, other than a catch can what can be done to mitigate how much oil is making it's way into the intake manifold from the crankcase? A small inline filter?

 

First we have to talk about some specific engine type and year range. Because SBC tend to behave quite differently than an OEM LS style engine for example, the SBC is far more varied, from the factory they can be quite different in terms of seal behavior and internal structure positioning and so forth. SO, for us to be fair with our general statements, It serves to narrow down the scope of our discussion to more effectively use blanket statements which can apply to any engine within that range.

I Like to limit my power&pcv discussions to the 'ancient' (20 years old now) yet modern subset of V8 truck engines from Chevrolet (made after 2002 but before 2008, such as LM7 and L33 and LQ4) because it levels the playing field for performance venue (they all support 800-1200-1600bhp), as there is nothing significantly superior produced since then due to their computer aided design and relatively simplicity of electronics for people interested in swapping their vehicle (LS swap) while also lacking the troublesome modern devices as DOD, direct injection, etc... which complicates a swap in any engine made after roughly 08+.

If we take a sample size of those engines with between 80,000 miles and 250,000 miles we would find they all produce similar blow-by, whether they are 300hp or 1200hp makes no difference. The use of modern engine oils and modern engineering techniques makes possible to find a mint set of bearings in almost every single one of them with any mileage it seems.
For example the 700-800hp LM7 in my car right now has over 200,000 miles and produces some blow-by of course, but it isn't any extra when compared to any other 300hp engine from those years.

This makes it very easy to blanket statement the following:
Blow by gas from any healthy engine (any one of THOSE healthy engines which has been maintained) should be quickly returned to the combustion chamber because it will not contain significant oil residue or gas state oil molecules when the PCV SYSTEM is properly setup. In other words, the blow by gas from those engines contains very little oil, whether 300hp or 1200hp, it is mostly a combustion byproduct which are light carbon chains consisting of partially reacted hydrocarbon compounds from gasoline. Being light chains similar to gasoline means they will function similar to gasoline: They will CLEAN as they move along while in a gas state. Thus the blow-by gasses from those engines functions almost as a cleaning detergent as long as it remains as a gas state and is quickly whipped back into the intake manifold while still hot and fresh, and like any maintained PCV component the line should be replaced at some interval of course(maybe every 5-7 years?) to eliminate the small collection which still occurs over time. This requires a properly setup PCV system which I have gone to great lengths to describe already above but will attempt to do so again.

The problem people introduce unknowingly is they create a difficult pathway for those hot fast moving gas molecules which causes them to slow, cool, settle out, and combine with other similar molecules, forming hard or sticky substances we find later over time.
Another problem is the overall flow and design of the PCV system which I will now discuss again.

The crankcase must be kept at a vacuum of 1 to 3" Hg at all times, cruise, idle, wot. This pressure drop must be measured and set in a performance application. It depends heavily on the correct paper air filter and correct PCV hose attached after that air filter, especially in turbo applications.

If the crankcase vacuum isn't able to reach 1 to 3" Hg of vacuum, the engine blow-by will increase. Crankcase pressure will increase (by definition if you don't have a vacuum, you have pressure, nothing can be zero perfectly because the engine operates in pulses and each piston brings its own pulse into the crankcase rising pressure, or attempting to rise pressure with each pulse. Thus a vented crankcase is actually under pressure at all times and this will increase blow-by and reduce piston ring function).
To put this another way, the piston ring seal is DESIGNED to work with a vacuum inside the crankcase. Automotive manufacturers use PCV fresh air inlet restriction orifices since the 80-90's, especially in turbocharged variants as the infamous 2jz-gte and sr20det and similar, in order to facilitate the crankcase vacuum which allows the piston ring to function properly.
Without that 1 to 3" Hg in the crankcase, piston ring will not function properly, so blow by will increase in a semi-positive feedback mechanism.
In other words if we measure the blow by of an engine running at 1psi crankcase pressure compared to an engine running with -1.0 psi crankcase pressure, the engine with 1psi will produce more blowby because piston ring seal cannot function properly. This is the root cause for majority of blow-by issues in any engine, that is, improper PCV setup. Usually because of air filter modifications.

The OEM style paper air filter and inlet tract is DESIGNED to protect pcv function by producing a pressure drop of approx 0.5" to 1.5" Hg, and more (3"+ Hg for dirty filters) which applies to the crankcase during wide open throttle. By keeping the crankcase in a vacuum state at all times this will reduce the total blow-by of an engine, as well as protect the engine oil by pulling light hydrocarbon chains out of the oil and out of the crankcase before they can interact with engine oil. The engine is able to lead a long healthy life this way, even with less frequent oil and filter changes, because as the engine is more neglected the pressure drop is increasing- and this is by design, cunning engineering allows the neglected engine to more heavily clean its crankcase due to the increasing pressure drop of the mal-maintained air filter system. But I digress

The points to take away are summarized:
1. Air filter must provide a pressure drop of 0.5" to 1.5" (or up to 3" Hg) during wide open throttle to maximize piston ring function.
2. Part throttle and idle blow-by of healthy modern engines should be directed to the intake manifold quickly, short and sweet, using minimal hose and OEM size diameter through a high quality PCV valve (use 1998 toyota supra turbocharged PCV valve for good results, IMO).
3. Measure crankcase pressure at idle/cruise and fix the fresh air inlet diameter to match the desired 0.5" to 1.5" Hg pressure drop minimum (as in the picture I posted above)
4. keep all lines as short as possible, do not introduce any additional VOLUME to the system, such as catch cans.


There is a reason to use a catch can, I will address quickly:
Engines which are damaged, broken pistons, or poorly manufactured, poorly machined, improperly assembled, improperly broken in, etc... Any engine which is damaged may have a problem with oil control, oil spilling out somewhere uncontrollably, can use a catch can as a bandaid, so the owner can drive the car temporarily until it can be fixed.

Thus when we see a catch can we can assume there is some oil control issue, either the owner or machine shop didn't assemble correctly or they don't know about the importance of pressure drop in the crankcase to support piston ring function which over time, is similar to the effects of smoking, initially there is little sign but over time symptoms develop which cannot be easily or quickly corrected even if you "Stop smoking" (setup the pcv properly, finally) due to the wide spread effects over time of improper PCV.

 

I thought I posted the picture but its in the link I posted, not in this post yet. But here it is simply drawn in paint quickly


For IDLE/CRUISE:

Wide Open Throttle PCV:
This one showing how to measure with a sensor and select for air filter

 

Better BY FAR than fiddlefarting around with a bunch of that, is to go DIRECTLY TO THE SOURCE of suspected "blowby", and deal with it.

The 2 biggest sources in a typical reasonably well-maintained (oil changed every few tens of thousands of miles whether it needs it or not) small block Chevy are, the intake manifold gaskets, and the valve guides. People ALWAYS want to jump directly to the piston rings, especially the end gap, but that's not usually the case.

Valve guides wear out, and the valve stems, where they pass through the guides, wear as well. On the intake side, that exposes the crankcase (the inside of the valve cover) DIRECTLY to intake manifold vacuum; and on the exhaust side, exposes the crankcase DIRECTLY to the exhaust ports. Install "positive" valve guide seals; NOT the stupid-a$$ O-rings the factory used, NOT "umbrellas"; POSITIVE type only.

And of course change the intake gaskets. Piece o cake. They turn to dust and crumble in the center, where the exhaust goes through the center of the heads and into the intake, for EGR. This exposes the crankcase (lifter gallery) DIRECTLY to the exhaust system. Just replace them.

Then AND ONLY THEN, maybe get all wrapped up in the rest of that crap, which is about 99.999% assured of being a useless waste of time anyway. Pretty drawings and a pretense of technical sophistication don't necessarily align with COMMON SENSE. Start with the simple stuff FIRST. (speaking strictly as a former math & physics major)

I would also recommend doing these 2 things, BEFORE changing the oil viscosity.

 

Modern OEM LS engines dont have issues with valve guides or whatever. The real problem is people modifying their intake air filter and not measuring their pcv system pressure.

Also I am not sure what you mean by "all of that crap" when all I've done is show how the OEM PCV system is routed. There is nothing special or different here in anything I've written, its all OEM information.

Finally, the PCV system is the most important system on an engine, it works directly with the oil system, oil pump, to provide oil control. So mastering it is essential for high performance. In racing we use vacuum pumps instead of intake manifold vacuum, and those systems are tightly monitored and controlled. Without understanding the basics of pcv you cannot ever hope to achieve mastery of high performance engines.