Which PCV Valve to use???

**Ace17** · 01-04-2020

Hey guys,

I've got a Vortec TBI build in progress, and I was wondering which PCV valve to use. I have an 1988 GMC sierra that I'm rebuilding, so I bought a new vortec 5.7 long block, and put a vortec/tbi intake on it. It's got a mild cam(comp cams xe258hr), 1.6 rollers, nothing too crazy. My question is, should I use the pcv valve made for the 88' tbi engine(FV184), or the one for the 96 vortec engine(FV178)? I had a friend tell me a while ago that using the wrong pcv valve on your engine can lead to leaking gaskets and seals, as it helps vent the pressure in the engine. What do you guys think, considering it's both vortec and tbi?

**1project2many** · 01-04-2020

You'll be fine with either valve. There's even a chance they're the same valve with the addition of a plastic elbow on one. Make sure the breather in the opposite valve cover is open because that's where any crankcase vapors that cannot be drawn into the PCV are vented.

**Ace17** · 01-04-2020

Okay cool. I was questioning how different the pcv valves would be, considering these engines aren't radically different from each other.

**PlayingWithTBI** · 01-05-2020

Take a look at this one

https://www.summitracing.com/parts/n...7779/overview/

**Ace17** · 01-05-2020

Wow, that pcv valve looks like it works for the tbi trucks, and then a few of the 1996(and later) trucks as well. I'm so confused, lol. I think I might just buy a few and try them all out

**LeMarky Dissod** · 01-06-2020

What the original poster suggests
in this thread
may not be overkill if your cam and either of those PCV valves are not in sync.

At a minimum, you may want to do some research regarding Part Number 12572717. Technically it's not a PCV 'valve'; it never opens or closes, because it's a fixed orifice.
Originally redesigned in 2003 to combat oil consumption in Gen3 GM V8s of all sizes, many LT1s, L31s, and even older GM V8s have used this PCV fitting with great success.

Hope either of the pieces of info in this thread are of some help to you …

**Ace17** · 01-09-2020

Yeah I'm not opposed to trying any of these suggestions, because at this point I'm starting to run out of ideas.

Not to hijack my own thread, but I'm currently dealing with a oil pan leak right at lip where the oil pan meets the timing cover. I've replaced the gasket at least 3 times and it still leaks(the one-piece felpro gasket). While the engine runs, it's totally fine, but as soon as I shut it off, it squirts out of the bottom lip of the oil pan. I've heard from several people that it could be because of a buildup of crankcase pressure, so that's I'm currently looking at the pcv valve system.

Do you guys have any more suggestions as to what it might be???

**Fast355** · 01-09-2020

Originally Posted by Ace17

Yeah I'm not opposed to trying any of these suggestions, because at this point I'm starting to run out of ideas.

Not to hijack my own thread, but I'm currently dealing with a oil pan leak right at lip where the oil pan meets the timing cover. I've replaced the gasket at least 3 times and it still leaks(the one-piece felpro gasket). While the engine runs, it's totally fine, but as soon as I shut it off, it squirts out of the bottom lip of the oil pan. I've heard from several people that it could be because of a buildup of crankcase pressure, so that's I'm currently looking at the pcv valve system.

Do you guys have any more suggestions as to what it might be???

With the engine shut-off the crankcase pressure will be gone in a fraction of a second.

My guess is its likely leaking at the timing cover or at the bolt that intersects into the fuel pump pushrod cavity if you have changed the pan gasket 3 times.

Do you have the oil pan reinforcement bars in place?

Did you clean the block where the pan sits completely with carb or brake parts cleaner and put a bead of RTV on all 4 corners where the pan gasket meets the timing cover and the rear main seal housing?

Stock vortec timing cover is also one time use. Once its torqued into place and removed, you throw the timing cover and bolts in the trash and get a new one. If you reused the cover swapping the cam it could be your leak source. I have a Holley Aluminum cover on my L31 based 383.

**PlayingWithTBI** · 01-09-2020

You should have a PCV valve on one valve cover going to the base of the throttle body, and on the other side should be an open hose that goes from the valve cover to the back of the throttle body neck.

**JCampbell** · 01-09-2020

I just finished an L31 TBI build in my 86 K20. I'm using the stock LO5 PCV.

One interesting thing I learned is that if you don't have a proper vent on the other valve cover to allow clean air into the crankcase, you will build a vacuum in the case and it will pull air in through the rear main seal. It will cause an intermittent squeak or squeal that will drive you crazy.

I lost the plastic vent tubing that went from the valve cover to the air cleaner and couldn't find a breather to fit, so I temporarily plugged the hole with a spare PCV valve. The squeaking freaked me out. Thought I was loosing a bearing or something.

**Ace17** · 01-09-2020

Fast355 - You've got an aluminum cover on your vortec engine??? I was looking around for a metal cover at the time of building this engine, but I couldn't find one. I never liked the idea of putting a plastic timing chain cover on an engine; plastic has a tendency to warp with age.

Yep, I've got the reinforcement bars in place, and I spent an hour cleaning everything up with brake cleaner and acetone. When assembling I put 4 dabs of black rtv in the corners where the block meets the timing chain cover. This area on the engine is actually bone dry.

I normally don't touch the timing cover when I change the oil pan gasket, because there doesn't seem to be a leak anywhere above the lip of the oil pan. It's the strangest thing(I might shoot a video of it eventually), but whenever I am running the engine for a while, and I turn it off, about a tablespoon of oil gushes from the middle of the lower lip of the timing chain cover/oil pan junction.

**Fast355** · 01-09-2020

Originally Posted by Ace17

Fast355 - You've got an aluminum cover on your vortec engine??? I was looking around for a metal cover at the time of building this engine, but I couldn't find one. I never liked the idea of putting a plastic timing chain cover on an engine; plastic has a tendency to warp with age.

Yep, I've got the reinforcement bars in place, and I spent an hour cleaning everything up with brake cleaner and acetone. When assembling I put 4 dabs of black rtv in the corners where the block meets the timing chain cover. This area on the engine is actually bone dry.

I normally don't touch the timing cover when I change the oil pan gasket, because there doesn't seem to be a leak anywhere above the lip of the oil pan. It's the strangest thing(I might shoot a video of it eventually), but whenever I am running the engine for a while, and I turn it off, about a tablespoon of oil gushes from the middle of the lower lip of the timing chain cover/oil pan junction.

Mine has the hole for the crank sensor but Holley makes it both ways. If you ever want to run a sensor in the one cast shut, a relatively simple machining process could open the hole. Then again the whole cover was reasonably priced. ~$65.

Are you sure the timing cover is not cracked or missing part of the rib that holds the gasket into place.

**Ace17** · 01-09-2020

Yep, the bottom of the timing cover is in good condition. It actually looks like it's leaking from bottom of the oil pan gasket mating surface, as opposed to the top where the gasket meets the timing chain. I'm gonna be out in the garage a little later, and I'll see if I can shoot some pictures to show you what I'm talking about. If I can, I might even get my dad out in the garage and I can film the oil coming out of the oil pan front lip as the engine is shut off.

**Ace17** · 01-10-2020

UPDATE! Okay, it looks like it's leaking a little higher up than I thought! It's coming from the upper corner of the oil pan and leaking down. I put black rtv there(as seen in the video), but it didn't seem to make a difference.

https://www.youtube.com/watch?v=WYI_sdXgBI8

https://youtu.be/4-C9S7T0MDc

**1project2many** · 01-10-2020

One interesting thing I learned is that if you don't have a proper vent on the other valve cover to allow clean air into the crankcase, you will build a vacuum in the case and it will pull air in through the rear main seal. It will cause an intermittent squeak or squeal that will drive you crazy.

Lol... my first ever post on the 'net was telling a guy with a '59 Chevy truck that the horrendous squeal he was hearing at idle was because he had installed two PCV valves on his engine.

UPDATE! Okay, it looks like it's leaking a little higher up than I thought! It's coming from the upper corner of the oil pan and leaking down. I put black rtv there(as seen in the video), but it didn't seem to make a difference.

Are you using a pre-96 block? the Vortec cover does not fit the old blocks correctly. I made an aluminum plate to help the timing cover seal against the block. I still needed some RTV for the corners.