For a few months I've been wondering what's been going on with my engine. It seems healthy, but it burns oil, and the #2 plug fouls with oil almost immediately. My first thought was that the oil control rings were toast. The first few thousand miles on this engine were spent with the PCV system hooked up wrong so that the crankcase was getting full manifold vacuum, and word has it that this can pull oil off the cylinder walls. However, this didn't sit quite right with me. The #2 plug would be wet with oil when I pulled it, which didn't seem to me like rings. I wondered if it could be valve guides, but the heads were fresh. I figured I would just sit on it, because I'm planning a full engine rebuild later this year, but the other day I noticed it was steadily puffing out wisps of smoke at idle.

I recently bought a cheap USB endoscope with the intent of using it to diagnose this. I figured the time was now, so I pulled the #2 spark plug and poked it into the cylinder. I was happy to see that the crosshatching still looked good, but the top of the piston was disgusting.





I should also mention that I've previously fought with by wideband O2 showing the passenger side running lean at idle. I had a lot of theories but not many options to test them. They were mostly implausible, but one dawned on me a few weeks ago that seemed like the silver bullet. I'd heard of guys having vacuum leaks inside their engine, between the intake manifold and the lifter valley. Not only could this lean out one cylinder in particular (making one whole bank look lean), it could also allow oil to be sucked in and burned.

This might be the first time a SuperRam intake ever made anything easier. By just pulling the lid off, I had a straight shot down the intake runners with the endoscope. Sure enough, oil seeping past the gasket. Or at least I think that's what I see; hard to tell with the image quality. I poked it down all the other runners, and none of them looked quite like #2. Most had some glossiness, but not the yellowish smear of oil from #2. That said, I'm not totally sure what the shininess would be. It almost looks like RTV, but I'm 99% certain I just put RTV around the water jacket. Who knows though.


#2 cylinder


#4 maybe? Wish I'd kept better track.


#7 I think?


Any thoughts on what I did wrong to get oil coming past the gasket here? I'm sure I torqued the bolts by the book (from the inside out, rotating pattern, 35 lb-ft. if I remember?). I think I used the red tacky glue to hold it in place when I installed the intake.

Also, I definitely recommend getting a cheap endoscope like this. I've used it a few times, even for stuff like looking for a nut I dropped down in the engine bay. For $20 it's nice to have on hand.

 

I don't think that's RTV or anything that you did to cause a problem. It could be (spit-balling here) that the head or the runner has a nick / scratch in it that doesn't allow the gasket to seal completely, and that's allowing oil to get sucked in as you say. Those look like the OEM GM gaskets?

 

I recall both surfaces as being pretty clean and smooth, but it's been a few years. I'm pretty sure I'm running the gaskets from this Fel-Pro set.

 

Sorry, I thought you were talking about the lower intake manifold gaskets to the heads, no? The 35lb torque made me think lower manifold to heads. Or are those indeed the SuperRam runners to lower intake manifold themselves?

 

Ahh, my bad. You are correct. I guess I just grabbed the first thing I saw when I searched my records for "intake gasket". I can't find which particular gasket I used, but I generally stick with Fel-Pro.

I went back and got better pictures of the gasket in all cylinders. Here they are in order (#1, #2, #3, etc.)










I still only definitively see oil on #2, but the others do look pretty crusty. It could be RTV, but I think it has to be oil. Maybe it just wicked into the paper rather than leaking past it like I think it is on #2?

Now, I did see oil one other place, and I can't explain this. This is a picture of the gasket between the runner and the intake base on the #1 cylinder. I really cannot fathom how oil would be getting here. I think the only thing upstream of that is EGR, but I can't imagine much unburnt oil making its way into the exhaust. Only thing I can think is maybe a valve cover leak letting oil pool at the outside of the base of the runner, then getting sucked through, but that's a wild theory.

 

Yeah, I think you're right and that theory is too wild to be correct.

So if your avatar is the 1990 coupe that we're talking about here, and if my 1989 is anything similar in crankcase PCV routing, there is a PCV valve in the left valve cover which provides positive pressure ventilation of oil fumes into the intake manifold base, and the right valve cover has an oil vent / breather hose which attaches to the throttle body providing negative pressure suction of air back into the crankcase when needed for pressure balance. I have seen liquid oil gather in both of these hoses left and right, and I think they have some ability to allow enough fumes / oil mist liquid to be sucked into your inbound air behind the throttle plates.

I know you wrote that you've got the SuperRam, and I'm not super familiar with how the airflow dynamics work in that manifold, but the combination of places where you show some oil mist accumulation could just be where the airflow has a slight disruption and allows oil mist to gather there when it's sucked into the intake air charge via those PCV hoses. In other words, the oil films that your endoscope are showing may just be normal accumulation and they're not the cause of your actual oil burn and lean condition mentioned.

I think your earlier theory is probably most likely; that you have valve guide seals that are leaking (probably near that intake #2 valve that you see the plug fouling) and when you replace those valve guide seals it will help. This is just theory based on what you describe, and I'm sure someone on here has potentially better ideas that I've not thought of.

AJ