Does oil go backwards, against airflow?

Jerome74911S · 02-16-2015, 03:02 PM

At first I thought I had a failed valve guide oil seal, but now I'm not so sure. There is a large deposit of ugly junk in my #2 intake and that spark plug looked black and oily, but can oil from a failed oil seal make its way 'backwards' up the intake runner tube? The tube is oily inside all the way up to the point where it plugs into the air box.

Here is the seriously dirty intake valve area of cylinder #2.

Whereas, here is #1, nice and clean, as are all the others.

And here is the 'top' end of #2 intake runner, where it plugs into the air box. Looks oily and otherwise dirty, but #1 is clean.

So, if it is the cold start injector and/or its controls not working properly, how does the gas gunk, or oily gunk go up the intake tube against the airflow? Or, if it's a leaking oil seal, same question. What's happening?

Elombard · 02-16-2015, 03:17 PM

Interesting, I was going to say the oil is coming from the recirc vent system but that should make all the runners dirty I would think.

I think when the valve slam shuts there is quite a bit of turbulence but looking forward to others chiming in.

T77911S · 04:25 AM

just a guess, but if oil is leaking past the valve guide, when the other cylinders are on their intake stroke, that could pull the oil up an into the runner.
i would think this would be reall bad when you are at hi revs and close the throttle. that would put more vacuum on the on the intake system.

you might do a leak down test.

stlrj · 06:57 AM

It appears that any oil that has puddled at the bottom of the air box overnight will be sucked in by the bottom runners nearest the floor of the airbox, that is, #2 and #5 on startup. In addition, if you were to routinely park at a slight angle to the left, you would find most of the oil being ingested into #2 runner as the engine goes poof in a cloud of smoke at first start in the morning.

Just a thought...

Cheers,

Joe

wwest · wwest's Garage

Valve not fully seating?

Compression measurement?

stlrj · 02-17-2015, 09:24 AM

You might notice that where #1 attaches to the air box is on the top part of the box in a clean dry location and #2 is on the bottom where oil is likely to puddle.

And here is the 'top' end of #2 intake runner, where it plugs into the air box. Looks oily and otherwise dirty, but #1 is clean.

Josh D · Josh D's Garage

What does #5 look like? Both #2 and #5 pull from the bottom of the air box.

Jerome74911S · 02-17-2015, 10:25 AM

Quote:

Originally Posted by Josh D

What does #5 look like? Both #2 and #5 pull from the bottom of the air box.

Someone else mentioned this idea, too. I park on the level, and #5 is running as clean as a whistle. When I took off the air cleaner there was very little oil to be found in there.

There is a lot of good speculation given here, but naturally I want to be pretty sure of what to dig into with the most confidence, so keep scratching your heads, please. I'm going to get my hands on a compression tester and start with that.

Elombard · 02-17-2015, 10:44 AM

Hmmm yeah that would be nice if the valve was adjusted too tight and not seating and all you had to do was adjust it. If you are able to determine its the valve seal I am not sure I would fix it if its not running badly. The rest of the ports look great.

Not sure a leak down will be definitive if its a valve seal. Unless its real sloppy seams like that valve would seat most of the time and not show any leak by unless you wiggled it?

wwest · wwest's Garage

Quote:

Originally Posted by Elombard

Hmmm yeah that would be nice if the valve was adjusted too tight and not seating and all you had to do was adjust it. If you are able to determine its the valve seal I am not sure I would fix it if its not running badly. The rest of the ports look great.

Not sure a leak down will be definitive if its a valve seal. Unless its real sloppy seams like that valve would seat most of the time and not show any leak by unless you wiggled it?

Use the engine itself to compress... valves then have to unseat-reseat, etc, etc.

Note that in the picture the valve seems to be mostly absent of crud on one side, where the leak is?

Jcslocum · 02-17-2015, 02:52 PM

Valve overlap allows air to go back UP the intake while running as well as the vacuum that is in the intake when running. If oil pools up while sitting it could also be sucked/blown up when starting.

THat is a mess and I don't know on this type of system if there is something specifically connected to that intake or in the air box nearest that intake....

Walt Fricke · 02-17-2015, 11:00 PM

Err -- this is obviously a CIS car, but I don't find any other information.

The 2.7s had the oil tank vent (which includes the engine vent) connected to the airbox on the engine side of the air filter.

The 3.0s (ones I am familiar with, anyway) have this connection go to the rubber boot joining the two sides of the CIS intake system.

In either case, one would expect blowby oil to end up about everywhere in the intake system downstream from where it got in. So this is a puzzler.

I'd do a leakdown and a compression test to see if the #2 shows up any different than the others. The theory that the valve guide is pretty worn, so on the intake stroke oil is sucked down it into the port, and that the intake doesn't quite seal on the compression stroke, forcing air and some oil up the intake runner, sounds at least plausible. A leakdown ought to tell you if there is any validity to such a supposition.

reddogmotrsprts · 02-18-2015, 12:34 AM

I can't believe the other runners would so perfectly clean if the source of oil was from the airbox. Also, the uniformity of filth and distribution in the runner suggests vapor to me and not a little drip from puddling oil.

My money is on a broken valve spring; I think if you were leaking oil from a stem seal, it'd simply be washing right into the cylinder and would remain fairly clean. I guess if you're very lucky, the valve simply isn't seating due to debris.

T77911S · 02-18-2015, 04:51 AM

the only way oil can go up the runner like that, and that is a LOT of oil, and there not be a lot of oil on the others is if there is a lot of oil leaking past the valve then the other cylinders are sucking the oil up the runner when you let off the gas.
the oil is being spread out to the other 5 cylinders. that is why the others are clean.

i suggested a leakdown because there could be a slight chance the valve is not seating and the compression is blowing it up the runner. but the car would run bad. you might not notice this except the person driving behind you would see smoke when you lift.

how many miles are on the motor

there is not enough valve overlap on a 2.7 or 3.0 to blow that much oil up the runner.

psalt · 05:21 AM

Does oil go backwards, against airflow?

that spark plug looked black and oily,

Jerome,

To answer your question, yes, on a running engine the intake manifold is a swirling mess of air, fuel and exhaust pulsing back and forth. With that amount of oil in the intake port, I would be also be looking at the piston crown and ring seal for that cylinder.