Plenum Gasket.
 

Found my coolant leak. Intake. Looks like the plenum gasket. How much trouble am I getting ready to get into? I've never done anything much more invasive than starters and water pumps. Anyone got a step by step guide for performing this procedure?

It's going to take more than starters and water pump ;) But not much, all it does it involve removing the 7 plenum bolts, removing the TB,TB cable, fuel rail/injectors, prying and loosening, and taking it off. Of course there is a little more to it, here is a link on the procedure:
http://www.gmtunerz.ca/docs/3_4upperintake.pdf

Welcome to the forums

You never mentioned the engine type so I assumed a 3.4, a 3.8 shouldnt be much different, maybe a bolt or 2

Yeah, sorry bout that. 3.8. Thanks for the link. I'll get to reading it and see if I can do this.

Are you sure its the upper intake? Intake gaskets and the plastic elbow under the intake are very common issue with these cars.

Very true^They tend to damage alot easier than the upper intake

Well I went ahead and changed the upper gasket. I am pretty sure that's where the leak was, as there is staining on both sides of the intake just below that gasket going down to pools of coolant between the intake and the valve covers. Those plastic elbows that you mentioned go from the tensioner assembly to the water pump, yeah? If so then those are brand new. (my old tensioner took a vacation as I was driving down the road a few months back) So those particular elbows are new, and lower than the evidence of the leak. As, obviously, are the other, lower, intake gaskets. Wish I'd taken a picture while I had it broke down so I could show you guys what I'm talking about.

From what we surmised coolant was leaking from the upper intake gasket, pooling on each side between intake and valve covers until it got up high enough to run over down the back side and burn off.

So there is definitely no more leak?(might have well have replaced the lower gasket as well since you were down there) Make sure you clean up alot where the coolant leaked and for extra measures run some seafoam through it and change your plugs and wires(the coolant might have fouled one or 2, have you checked?), then you should be on your way

I'm not prepared to say definately no more leak, but I'm pretty sure I eliminated it. Topped coolant off last night and it didn't take nearly as much as it was prior to replacing the gasket, and it's entirely probable that I didn't get it completely full saturday night after the gasket replacement. I haven't seen any fresh coolant where it was pooling before.


As for plugs I changed them recently, and none of the old ones were fouled. (I changed them after the coolant leak started but before I found the apparant source) I had one injector that looked like it might have been a little cleaner than the other five, but the difference wasn't big enough to cause concern, and I haven't had any rough ride trouble accelerating problems that aren't obviously being caused by a backed up Cat (next project). I have no coolant in my oil. (changed it last night and it was spotless)

Would have done the entire intake if I'd been able to afford the full gasket set, but the money wasn't there this weekend. I may have to go back and do it anyway, but if I do I'll chalk it up to 11 bucks in stupid tax for just buying the upper.

In a few more days I'll be able to confidently say if the leak is gone or not for sure.

Is it too late to run the seafoam through there now?

there is very definately still a leak. Looks like the same place, but only on one side of the intake this time. My cousin/help tightened the bolts on that side, so my first stop is to check those. After that I guess I break back in and double check to make sure it's not warped or cracked somewhere I didn't see. Any other ideas about where it could be coming from? I can't see how a lower intake leak would show up that hight on the engine.

Which side of the intake is the leak on?