GM 3.6L LY7 V6 Bypass and Anti-drainback

[ktrsb]

Can anyone explain to me the functions of the valves in the filter adapter and filter adapter cap in this top loading, cartridge-style GM engine:

Specifcally, GM calls parts nos. 8 and 10 both "bypass" valves. The one that fits in the cap is apparently replaceable.

The reason I ask is I believe I have fixed a startup noise that sounded a lot like lifters pumping up or timing chain rattle just by replacing the cap. The engine has 167K miles, a history of moderate sludging, and a recent timing chain replacement. The noise preceded the timing chain replacement, but was lessened after.

I am curious as to how these valves work, why there are two, and whether one is actually a drainback.

Thanks in advance.

 

[Maritime Storm]

GM has been having issues on the direct injection model of this engine(you didn't specify year and model) with early timing chain failures. As it sounds like you've already encountered. It could be the old cap's bypass valve was defective.

 

[JR]

had motor and vehicle is this in.

 

[ktrsb]

Originally Posted By: Maritime Storm
GM has been having issues on the direct injection model of this engine(you didn't specify year and model) with early timing chain failures. As it sounds like you've already encountered. It could be the old cap's bypass valve was defective.


OK, not to be rude, but this really isn't the information I was looking for. Engine had 160K+ miles, and I am well aware of the timing chain issues, that's why I didn't ask about them. The whole question is, was the bypass valve defective? I can speculate just like anyone else. I am just asking someone who knows.

 

[dnewton3]

No - I don't own one of these. But I don't have to own one to be able to follow a simple hydraulic circuit.

You are correct; one is a bypass valve and the other an ADBV.

I presume 17 is the pressure sensor, so conventional design wisdom would lead me to believe that 8&9 are the bypass and 10&11 are the ADBV. I say this because you cannot have the ADBV leading into the filter in normal flow, because when the oil wants to drain back, it would just seep through the media; the ADBV must be AFTER the media in "normal" flow mode.

(Note - I'm presuming the ADBV is 10&11 because there is a dotted line indicated it's internal to the rest of the package.)

In short, the bypass valve is a relief valve; they are to work in the same direction as normal fluid flow, based upon some predetermined pressure differential. The ADBV is a check valve, it is "activated = shut" when flow is reversed. Hence the positions to achieve those tasks.


Why GM calls them both bypass valves is beyond me, but much of their literature is confusing ...


BTW - that is one clean engine bay for having 167k miles on it.

 

[ktrsb]

Originally Posted By: dnewton3
I say this because you cannot have the ADBV leading into the filter in normal flow, because when the oil wants to drain back, it would just seep through the media; the ADBV must be AFTER the media in "normal" flow mode.


Thanks, that is what I was looking for. I believe I will fashion a test based on a "pop-off" tester I made for my jet ski carbs - I think I have read that it should be 21 psi for these bypass valves. But I have blown through it and know it is not stuck open.

Originally Posted By: dnewton3
BTW - that is one clean engine bay for having 167k miles on it.


Lol. I wish. Not my engine - I keep my pix on shutterfly and bitog.com doesn't play well with them.

Check out srxturnsignals.shutterfly.com.

 

[ktrsb]

So I pulled the bypass valve like this:

Found a PCV coupler that it fit perfectly in:

Used this setup to check its opening pressure:

Consistently was between 15 and 20 psi.

Video:

 

[dnewton3]

A man with tools and ingenuity; gotta love it!

 

[demarpaint]

Originally Posted By: dnewton3
A man with tools and ingenuity; gotta love it!


+1

 

[ktrsb]

So in my never ending quest to beat this topic to death, I improved my test device for use with my leakdown tester:

Hooked it up to my leakdown tester:

Found that it started opening at 10 psi, fully open at 21:

http://youtu.be/9Ej77mdj0XM

 

[ktrsb]

And of course, I couldn't leave well enough alone, so I dissected the valve.

The valve fits into a casting in the cap, with passages that allow oil to flow to the center of the casting where the valves is pressed in:

The very end of the valve is, of course, the seat for the valve spring:

The valve itself is just plastic and bullet-shaped.

The valve housing is just a sheet metal cylinder mated to a heavy steel housing. The cylinder has slots around the base on the valve end. As the valve opens, the oil flows through those slots and out between the sheet metal cylinder and the heavy steel valve housing.

No obvious signs of damage that wasn't caused by my hamfisted forensics, so I guess the spring just got tired after 150K miles or so.

 

[ktrsb]

OK, a long way to verify what dnewton3 already confirmed just by looking at parts diagram.

I always thought the anti-drainback valve was number 10 in the diagram. Whenever I would change the oil, I would push on it - it is spring loaded, and has a pin sticking up, so pushing down would "open" it (so I thought).

I now am certain that this valve is normally open, and pushing down on the pin closes it. So the design function is, when the filter cartridge is installed, and the cap is tightened, the metal base of the filter cartridge pushes down on the valve, closing it. When the cap is loosened, the valve opens, draining the filter housing and allowing for a very neat oil change.

I looked at the pictures of a previous oil change, and noticed something for the first time. Look at the ring that is worn/ polished into the base (it's missing from the "label" side, which I always install up):

It appears to me that the filter rotates as the engine runs, and the pin on the anti-drainback valve has worn this ring.

So next time I change the oil, I am going to test it out with some fresh oil and see if that is how it works. I am sure it is. I am also going to index the filter to see if it does, in fact, rotate.

OK, thanks to all, and thanks for letting me think out loud.

 

[gotib007]

Cool stuff, but what happened to the images?