Bad Head Gasket

[Colorado Yeti]

So, it turns out it was a leaky intake manifold gasket. Why a leaking intake gasket should make the coolant reservoir bubble under acceleration, I have no idea whatsoever. I checked the compression before I pulled it apart and they all had 150-165 psi in each cylinder with no leak so I quickly eliminated head gasket / cracked head from the variables. I changed the intake manifold gasket this weekend. Man, what a complete pain in the a$$!! I could have done this job in 3-4 hours on the 327 in my old '56 Chevy but it took me > 12 hours on my Tahoe and it is the exact same job. Whoever designed the power steering pulley / PS bracket / AC bracket contraption should be shot. But it runs like a dream and is clean as a whistle.

 

[willxfs]

Glad you got that all sorted out and your rig is running good again!

 

[swathdiver]

So, it turns out it was a leaky intake manifold gasket. Why a leaking intake gasket should make the coolant reservoir bubble under acceleration, I have no idea whatsoever. I checked the compression before I pulled it apart and they all had 150-165 psi in each cylinder with no leak so I quickly eliminated head gasket / cracked head from the variables. I changed the intake manifold gasket this weekend. Man, what a complete pain in the a$$!! I could have done this job in 3-4 hours on the 327 in my old '56 Chevy but it took me > 12 hours on my Tahoe and it is the exact same job. Whoever designed the power steering pulley / PS bracket / AC bracket contraption should be shot. But it runs like a dream and is clean as a whistle.

When you said vortec in your first post I figured you were dealing with an LS and not a SBC. The former does not have water jackets going through it. Glad it wasn't the head gaskets and she's running smooth.

 

[alpinecrick]

So, after talking to some guys who are very familiar with Vortec motors, they say this is a classic presentation of a bad intake manifold gasket which is a very common problem on this engine. They said this because I have oil in my coolant but no coolant in my oil. Of course, I don't know until I do a compression test and I haven't had time to do this yet. I'll let you guys know what I find. I sure hope it's an intake manifold gasket problem.

That's what I thought when I read your original post. The intake gasket generally leaks to the outside (usually in the rear) but can also leak coolant to the inside.

If the intake gasket is leaking, make sure you do't pump too much water into the motor when pressure testing.