Chevy 1.5T PCV system

JTK

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Aug 14, 2003
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Buffalo, NY
The PCV system on GM LYX 1.5L turbo engines really has me stumped. I had done some reading on how the tubing can get brittle and break on these systems, and all the fittings are basically a tamper proof, snap in place, one time use setup. The screws that holds what looks like the PCV valves themselves into the valve cover have tamper proof heads on them even.

While doing some maintenance on my new to me 2021 Equinox with the 1.5T, I took a good look at the one piece PCV hose assembly. The assembly connects to two stubs on the rear of the valve cover, which joins with a single stub on the front of the valve cover, then a single line tees off of this assembly and connects to the rubber boot just upstream of the turbo. Best I can tell, there is no vacuum supplied to this PCV system at all. The system appears to rely on what ever suction it can get from the turbo. All that oily condensation blows through the turbo, through the charge air cooler and into the throttle body. There is a small baffle box near where the system ties into the turbo inlet. I've seen videos where owners report this box full of oil/water. There's no easy way to drain it either. Here's a clip to get an idea of the plumbing.

 
they can not use manifold vacuum as the manifold is is often under pressure. The turbo is the only place it can get vacuum. A very low restriction catch can could also be used, it would need to be kept clean. The system needs improvement.

Rod
 
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You can't see the PCV that's used under vacuum, It's integral to the valve cover, cylinder head, & intake manifold. 3 in the diagram.



Operation.....

The crankcase ventilation system is used to consume crankcase vapors in the combustion process instead of venting vapors to the atmosphere. Fresh air from the intake system is supplied to the crankcase and mixed with blow-by gases inside the crankcase. Blow-by gases rise to the top of the engine and are picked up into the oil separation chamber in the camshaft cover, where oil is separated from the gases. Blow-by gases are then passed to the intake manifold to be consumed by normal combustion, through a calibrated orifice inside of the camshaft cover.

Fresh air is brought into the engine through the positive crankcase ventilation (PCV) valve (4) as long as the crankcase is under vacuum. The primary control is through the PCV orifice (3) which meters the flow into intake manifold, at a rate depending on manifold vacuum. The PCV orifice is an integral part of the camshaft cover. Under certain operating conditions, the system is designed to allow excessive amounts of blow by gases to flow through the PCV valves (1 or 2) depending on if the engine is in boost mode or excessive crankcase pressure is detected and then routed into the intake system to be consumed by normal combustion.

Turbo Applications:

During normal operating conditions the PCV gases are routed using PCV valve (3) and the internal passage within the camshaft cover. When the Turbo is active, check valve (3) is closed and check valve (1) opens and PCV gases are routed back to the turbocharger to be consumed by normal combustion. If the engine sees excessive positive crankcase pressure check valve (2) opens and the pressure is routed to the air inlet to be reintroduced into the engine.

Non-Turbo Applications:

During normal operating conditions the PCV gases are routed using check valve (3) and the internal passage within the camshaft cover. If the engine sees excessive positive crankcase pressure check valve (2) opens and the pressure is routed to the air inlet. Also for non-turbo applications check valve (1) does not exist.


In any application check valve (2) is only used if the engine sees excessive crankcase pressure.

pdiN6Tz.png
 
You can't see the PCV that's used under vacuum, It's integral to the valve cover, cylinder head, & intake manifold. 3 in the diagram.



Operation.....

The crankcase ventilation system is used to consume crankcase vapors in the combustion process instead of venting vapors to the atmosphere. Fresh air from the intake system is supplied to the crankcase and mixed with blow-by gases inside the crankcase. Blow-by gases rise to the top of the engine and are picked up into the oil separation chamber in the camshaft cover, where oil is separated from the gases. Blow-by gases are then passed to the intake manifold to be consumed by normal combustion, through a calibrated orifice inside of the camshaft cover.

Fresh air is brought into the engine through the positive crankcase ventilation (PCV) valve (4) as long as the crankcase is under vacuum. The primary control is through the PCV orifice (3) which meters the flow into intake manifold, at a rate depending on manifold vacuum. The PCV orifice is an integral part of the camshaft cover. Under certain operating conditions, the system is designed to allow excessive amounts of blow by gases to flow through the PCV valves (1 or 2) depending on if the engine is in boost mode or excessive crankcase pressure is detected and then routed into the intake system to be consumed by normal combustion.

Turbo Applications:

During normal operating conditions the PCV gases are routed using PCV valve (3) and the internal passage within the camshaft cover. When the Turbo is active, check valve (3) is closed and check valve (1) opens and PCV gases are routed back to the turbocharger to be consumed by normal combustion. If the engine sees excessive positive crankcase pressure check valve (2) opens and the pressure is routed to the air inlet to be reintroduced into the engine.

Non-Turbo Applications:

During normal operating conditions the PCV gases are routed using check valve (3) and the internal passage within the camshaft cover. If the engine sees excessive positive crankcase pressure check valve (2) opens and the pressure is routed to the air inlet. Also for non-turbo applications check valve (1) does not exist.


In any application check valve (2) is only used if the engine sees excessive crankcase pressure.

pdiN6Tz.png


Funny I was looking for this…lol.

GM doesn’t like to make anything simple……..
 
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Here's a little fun story that sparked my interest on the whole GM 1.5T PCV system in the first place. While I was doing some maintenance on my newly acquired 2021 Equinox, I inadvertently started and idled it for about 10sec with the oil fill cap off. In that little bit of time, enough oil mist and droplets shot out of the 710 hole that I had to wipe down the whole left side of the engine bay, fender, etc. It seemed like an awful lot of blowby for a 34k mile vehicle, which has supposedly seen excellent maintenance if you can believe a Carfax. The vehicle runs beautifully and has consumed no noticeable oil in the 500mi or so I've used it so far.

The oil fill hole is right near the timing chain, which I'm hoping is all the situation is.
 
That's the way most turbos PCV works nowadays I think. It's how my Gen Coupe is. They also have some sort of diverter valve too that will generate vacuum from the pre turbo intake track PCV make up air when under boost. Brake booster also needs a check valve. Check valves are internal to the hose and cannot be seen but you can feel them on mine.
 
I waited until '23 to buy my wife's Equinox. Didn't want to deal with the camshaft driven vacuum pump.
I would have preferred to go that route, but a used 2023 with the LSD 1.5T was a good $4K more than I wanted to spend. I believe the PCV system is the same between the LYX and LSD 1.5s, but it sure would be nice not to have the engine driven brake booster vacuum pump to contend with.

It seems like GM struggles with the PCV systems on everything they build with GDI or GDI and turbo. With the 1.5T's you have the potential of lots of oil and condensation in the charge air cooler, which has no place to go other than through the turbo. I've seen people report frozen charge air coolers in the winter time on these.

There is a little collection box looking appendage on the rubber boot upstream of the turbo on the 1.5s, but there's no easy way to remove and drain it. The PCV tubing is "permanently" attached, so you'd have to break things to have at it.
 
I'm hoping this engine is better than the 1.4T I had in a '14 Cruze. Worst GM motor I ever owned.
The plastic cooling system bits and plastic valve covers were pretty bad on those.

I think the 2018+ 1.5T does have some plastic cooling system parts, but I've not heard of any issues with them on the 1.5s. I've seen some reports of valve cover leaks and of course the aftermath of exploded brake booster vacuum pumps.
 
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