thick oil film inside intake manifold

[wwheeler]

I took off my cold start valve today for a rebuild. When I looked inside the intake manifold at the floor through the hole, I saw oil grunge. I wiped some out with my hand and sure enough it was quite oily. It wasn't puddled up but there was definitely a thick film. There was also some crusty black stuff like you would expect from the crankcase breather.

My question is, is it normal to have that much oily stuff in the intake. The breather tube is hooked up correctly for a '68 M130. Is there supposed to be a filter or screen other than the baffle in the valve cover? Could there be another reason for the breather gases to be that oily? The oil level in the crank case is correct and the engine doesn't smoke or use oil.

Thanks for the help. 

 

[Dash808]

I'm no expert, but I would imagine that there would be build up because of it. 

And It's funny you mention it because I just posted in my thread how the original owner directed my breather hose down and out the bottom of the car, and when looking at the exit area I can see grunge build up around the hose. 
I'm not sure of the effects of this but hopefully it isn't negative.

Doubt that helps you, but good luck.

[wwheeler]

Since I have been having problems with my cold start valve, I took it off again. This gave me an opportunity to see if anymore oil has collected in the intake manifold from the breather since I last cleaned it out in December 2008.

Well, more has collected. This time it is no longer grungy but is clean oil which means it collected between December and now. Just to check, I took off the brake booster and an accessory vacuum line from the back of the intake manifold. Both had a fair amount of oil residue inside the hoses as well. This seems to be more oil from the blow by gasses than I would expect.

What would be the cause of excessive oil in the crankcase gasses going to the venturi and intake manifold? Would driving habits have any effect? In an attempt to adjust the fuel mixtures and throttle linkage, my engine has done a lot more of idling than normal driving lately. In general I know this isn't good for our engines, but I wonder if it would increase oil in the crankcase gasses?

Any thoughts?

[rogerh113]

Hello,

How full is the trap (the plastic unit that looks sort of like a small elongated heart) between the brake booster and the intake manifold ?  If you don't have one, or it is full of oil, this could be a source of your problem (actually the booster would probably be the actual problem, but the trap should manage it to some degree).

Regards -- Roger

[waqas]

How full is the trap (the plastic unit that looks sort of like a small elongated heart) between the brake booster and the intake manifold ?  If you don't have one, or it is full of oil, this could be a source of your problem (actually the booster would probably be the actual problem, but the trap should manage it to some degree).

I'm not quite sure what the brake booster has to do with oil deposits in the intake. The most common problem with the brake booster is a ruptured diaphragm, which is usually caused by either a leaky master cylinder (brake fluid seeping into booster, damaging the rubber diaphragm) or simply age. Are you saying that a booster problem is somehow creating oily deposits in the intake manifold?

Isn't the plastic trap bottle on the vacuum hose supposed to trap brake fluid? (just in case it leaks from the master cylinder via the booster?)

[rogerh113]

Very true if the deposit is actually oil, which is an easy assumption to leap to.  It is possible that  the muck is aged gloppy brake fluid combined with old hose deposits.  I ignored my trap for a couple of years, and it was pretty much full - I figure that once full, the suction will pull that stuff down the vacuum assist line into the manifold. 

This would just be the first thing I would check, since this is the most obvious source of gooey fluid into intake manifold.

Regards -- Roger

[Benz Dr.]

If you had that much brake fluid getting into your engine it would be smoking by now. Brake fluid doesn't mix well with engine parts. Is your brake fluid going down?

This is engine oil from crankcase fumes combined with some fuel that comes out of the CSV. You could be running too cold causing a lot of condensation inside of the manifold, particularly in cooler weather. A fast drive at full temp will draw a lot of that stuff out of the manifold.
Normally, our engines have what's know as '' dry air '' going into the manifold. There should be little or no moisture entering the cylinder head and only at the point of the injector does any wetness occur. Engines with carbs have wet air filled with fuel droplets and heavier componets of fuel will fall out of the air stream and pool up in some areas of the intake. Over the years heat and air borne dirt will form a sort of crud that looks like carbon build up. It is, but not like in a cumbustion chamber.

Any fuel that isn't finely atomised at the CSV will pool up inside of the manifold and eventually form crusty deposits. This stuff won't hurt you for the most part but is sure isn't pretty.
If the CSV isn't working right it will only make things worse.

[wwheeler]

Thanks for the replies.

I checked the brake booster trap and it is dry. Also, I am not losing any brake fluid so I think I am OK there. Dan has a good point in that I have had a problem with a leaky CSV recently. Combine this with the fact that my engine has been idling because of all of the adjustments I have been doing during the cold winter months. Maybe this combination is doing it?


The port for the breather tube is in front of the butterfly in the venturi. When at idle, the butterfly is closed and vacuum is high behind the butterfly but low in front of it where the the port is. So from this it would seem that at idle, the draw of combustion gasses would be small. Even still, I haven't driven the car for long periods of time lately and possibly that is why the oil is building up.