Problem started with a bad coolant leak into the #5 cylinder. Pulled the intake and there was water setting in the #5 intake port. I assumed it was the manifold gasket because of their bad reputation. I heard GM had an updated gasket (read on here I think) but my only option yesterday was a felpro from advance. I never saw a bad spot on the gasket but water had to be entering there because the lower intake port was black and carboned but the port in the head was cleaner and had some rust spots (problem happened a week ago, just now got time). Cleaned all the mating surfaces impeccably, put a little rtv on the back of the gasket to hold it in place, and then bolted everything back together torquing the manifold in patterned steps.

...It still leaks water into the #5 cylinder. And by leaks it pours, it was shut off for 2 minutes and it leaked enough water to hydrolock it.

Any thoughts? My current plan is to hit up the chevy house for an OEM gasket set and hope that I somehow screwed something up putting it back together but I have a sinking feeling I'm just wasting more money days off. Thanks in advance for any help, the archived posts on this forum have already helped me out many times in the past.

 

Do a compression test on #5.

When you did the gaskets, was there any pitting on the mating surfaces of the head or intake around the water jackets?

 

There was very minimal pitting around the water jackets, nothing like what I've seen in some pictures on here. I'll compression test it this evening and hope against probability that it's not a headgasket. The only wierd part if it is the head gasket is how it literally fills the intake port in the head up.

 

Compression tested it. #5 cyl averaged ~135psi. Tested cyl #1 (135psi) and #4 (140psi) to compare it to*. Now I'm even more confused as this seems to point away from a head gasket. A blown head gasket or a crack big enough to hydrolock it should seriously effect cyl pressures. I guess it's possible I bumped the gasket putting the lower manifold on and caused another leak on the same cyl, (the #5 intake port is also a long way from the water passage) but not probable. I guess a warped intake or head could cause it. I didn't even think about checking them for straitness when I had it apart.


*What is the range it should be in anyways? I'm used to bikes that should be 180ish.

 

Hard to say where it should be. The 4.3L doesn't have an aggressive compression ratio so those sound about right. Generally, you want to see all cylinders within 10psi of each other. You definitely do not have a headgasket failure on your hands which is good!

You'll need to get it taken back apart for sure.

 

Hmm would putting flouresent dye in the coolant system and then running it work? I've never messed with any of it and not sure if they make it for coolant but this sounds like an ideal situation. And it still runs surprisingly well with the upper pelenium just held on by its own weight.

 

Well, I'm not sure what the dye will tell you. You know you have a coolant leak.

 

Yeah but I don't know where. If theres a big green streak between the coolant and intake ports I'll feel a lot better about just putting another gasket on. I don't really want to put another gasket set on there when the last one didn't seem to change a thing.

 

Well, you know it is getting into the #5 cylinder. Your possibilities are cracked head in the intake port (highly unlikely) or pretty much a bad intake manifold gasket seal (whether that is due to a bad gasket or mating surfaces not being flat, etc). Either way, you are looking at removing the intake again to check things out (straightness for one).

 

I just did the intake gasket on my 95 and I had to torque and retorque and retorque in order to get all of the bolts up to spec. The progressive tightening sequence loosens the other bolts as you go along. I know this seems obvious, but did you check all of the bolts final torque before you put everything back together? It does take several passes, even though they don't specificy it in the manuals. You should have used the tube of RTV black, oil resistant, high temp that came with the gaskets. Use brake cleaner to prepare surfaces? Did you tap and die boltholes and bolts, clean them (brake cleaner again) and use high temp thread locker? Wait 48 hours for RTVand thread locker to cure fully?

I read about a guy who went so far as to encircle each port, both sides of each gasket, with RTV to get a proper seal after he did it once and had this same problem.

You can put a short section of like #10 dowel (about 3/16 diam I think) into the bolthole to help you guide straight into position.

Also, and I know this is picky, but thereshould be3 bolts that you may have noticed are longer than the rest of the manifold bolts. Those need to go into the boltholes that have the engine hoist brackets on them. The longer length is to accomodate for the extra thickness of the brackets. If you use them in the wrong places, you can bottom out the bolt tips on the cast iron block downin the bolt holes, even though you have the impression they are pulling on the manifold.