Vent line from valve cover to air cleaner hose/fitting

I put this in the small block section, because I have a 350, but the big blocks use the same setup, at least in 69.

I've got a 69 LeSabre, which is supposed to use the 1 piece molded hose that connects directly to the valve cover. I don't really like that design, and would rather use the later design that used a grommet, a steel connector and a angled hose. Both hoses are reproduced, but I'd probably just use a piece of bulk hose. The steel connector is not reproduced. How are others addressing this connection?

What I did years ago (in the 90's) was to use heater hose and a gray 90 degree hose barb I found at Lowes. I never really liked it, as it can move around in the grommet, and is now bent by the heat/oil exposure. It will also contact the rocker arms if you press it into the grommet far enough.

Also...why does the hose connect to the air cleaner, if its not going to pull filtered air? It relies on a little filter pad instead of the main air filter.

 

Ok, it looks like after much time spent searching on vendor sites, and googling..... only after posting, I almost fell into a possible solution. Dorman actually lists a valve cover grommet for my 69, even though it didn't originally use one. It also fits the early 80's 3.8's, so I decided to explore what the 3.8 uses beyond the grommet.

The 3.8 uses this elbow. I'd rather have a strait connector for hose routing, but the 90 should work, too. I think this will be held by the grommet much better than the gray elbow from Lowes.

https://www.dormanproducts.com/p-24075-47043.aspx

Actual GM parts seem to be on ebay, too.

 

Airflow runs from the valve cover to the carb, not the other way

 

Got the metal barrel if you need that.

 

No, the PCV valve pulls from crankcase and the breather replaces what was removed. If airflow is coming from valve cover to air cleaner, the PCV isn't working or the engine is worn out.

 

Flow is actually in both directions. At idle and cruise it's in the breather and out the pcv to the carb but at WOT blowby exits the large hose to the air cleaner, which is why a large hose is needed. I run a 1" hose from the fuel pump block off plate straight up to the inlet. The hose is packed with 1/2 of a stainless steel pot scrubber for a flame trap.

Jim

 

When I was reading an old Chilton manual last night (One of the big books) they mentioned a flame arrester, too..... they were not specifically addressing a GM system, though. Should I have a flame trap on my car that was originally there, or is the filter providing that function?

The manual I was reading actually did not mention the direction of flow reversing, but I kinda figured there were times it could, although I doubt the PCV valve would flow much in reverse.

It still doesn't make much sense to me, why the vent line is outside the main filter. It just seems like a good way to foul the air filter with oil vapors wafting through it most of the time. In fact, my current filter is pretty dark, and I don't think it has much run time on it.... although it's years old because it sits.

 

Would you rather have all of that unfiltered blow by going through the carburetor? I'd rather replace the filter than have to clean out or overhaul the carb.

 

But you said the air is going the other way, and then Jim said it was going that way most of the time (idling/cruising).... the air from the PCV isn't filtered either, although I guess that's connected very low on the carb, or maybe it's actually the top of the manifold, I don't remember.

I'd rather have well filtered air going into the crank case, while preserving the main air filter, than rely on a little piece of poly, sitting in a cup, to do all the filtering going into the crankcase, while risking oil contamination of the main filter. My 1999 454 is setup like that, and has almost 300K miles.... I guess maybe MPFI isn't as susceptible to getting gummed up?

 

You DO have filtered air going into the crankcase.
The PCV valve only flows one way, thats INTO the carb AFTER it flows thru your carb air filter.
Under acceleration when your vacuum drops low enough to where the PCV valve doesnt function (closes) the crankcase blow by (pressure) goes thru that hose in the valve cover and the little filter collects any oil vapor so it doesnt completely saturate the engines air filter, thats why that little filter turns dark and oily.

 

That little filter does act as a flame trap. Maybe not a very durable one but better than nothing. The newer designs put it downstream of the air filter. Blowby does have combustion byproducts in it but that's pretty clean compared to unfiltered air.

Jim

 

Yes, filtered by the little poly filter sitting in plastic cup.... not ideal.

No it doesn't. The PCV is connected to the base of the cab, or the top of the intake. It does not go through the main air filter, as it would surly foul it.

Yes, the little poly filter is oily, but I was speaking of the main air filter.

 

Sometimes parts disappear over the years and owners, so I wasn't sure. For instance, I removed the dashpot years ago, but will likely put it back on since I still have it.

 

Slight misconception about how the PCV valve works. Flow through this valve is always in one direction only, it is the PCV vent line flow that reverses with blowby. Under high vacuum the PCV valve closes and then allows a metered flow through an orifice so that the idle mixture can be calibrated properly. At cruise and WOT the pcv valve opens and allows full flow to pull more blowby gasses into the intake manifold. The vent line allows fresh air to enter the crankcase during idle and cruise if the blowby is less than the PCV valve can flow. Then at WOT the increased blowby overcomes the flow of the PCV valve and reverses the flow through the vent line. This is why the vent line needs to be a large diameter. Not at all complicated once you understand how it is supposed to work.

Jim

 

I got my V6 elbow in the mail today, so I ran out to get the 5/8th fuel line..... doesn't fit. The elbow is 3/4". I guess when I did this back in the 90's I used 5/8ths because it fit the Lowes elbow, and I was able to jam it on the filter because apparently heater hose is soft enough to do so. I wonder if the 5/8" hose was functionally too small, since apparently original is 3/4". When I got this car, in the 90's it still had what I assume was the original hose, but was extremely mushy, and I think taped.

 

3/4" is common on the Buicks. I run a 1" vent line but I tend towards overkill.

Jim

 

I used a furnace humidifier drain hose, heated it to form fit the v/c 90* elbow piece. I think my 90* elbow was off of a 1968 350 maybe. It runs inside the filter area on my L88 base, no filter, no oil coming out either.
My pcv is direct from valve to intake, as I have zero vacuum provisions on my carb.
Might give you some ideas....