Fluid on exhaust causing smoke - 69 with 396 and auto.

[Slowboat]

Hi Everyone,

First post here. I have a recently purchased '69 C20 with a 396 and T400 auto trans. Earlier today I noticed a bunch of smoke coming out the back, especially when I went up a steepish hill. It isn't coming out of the exhaust, but either oil or ATF is dripping onto the exhaust (doug's Tri-Y headers) - it seems like it is hitting the passenger side header.

I got it home and noticed that the dipstick was out of the auto trans filler tube about 1". Would ATF come out of this - especially if you are going up a hill? The valve cover gaskets are leaking slightly (another project), would these get worse going up hill?

Anything else I should be looking for? I don't want to drive it too far until I get this sorted out.

Thanks,

Noah

[geezer#99]

You have a crankcase pressure problem!
Do you have a working pcv system?
Pcv in one valve cover and a breather on the other cover.

Post some pics of your motor.

[cableguy0]

Fix the known leaks and move on from there. If fluid is coming out of the transmission dipstick you have a clogged vent tube. ON hills you are getting into the throttle creating higher crankcase pressure especially if you don't have a good working pcv system like Geezer said. Pics would be great though.

[Slowboat]

Would it only happen going up hill? All other times it seems fine and I haven't had this issue. I was light on the throttle going up hill, and have gotten on it plenty of times on the flat and haven't had that issue. If the trans dipstick wasn't seated in the tube would fluid come out of it?

Here are a few pics from before the headers were installed:

[cableguy0]

Pcv looks ok EXCEPT you NEED a breather in that passenger side valve cover. The breather will filter the air coming in to the crankcase. Without it you are basically sucking in dirt and dust directly to the crankcase.


The transmission dipstick tube should NOT be pushing transmission fluid out unless you are upside down. If fluid is being pushed out of the transmission dipstick you have a clogged vent tube or another serious issue inside the transmission.


Badly leaking valve cover gaskets could be your issue. Under acceleration oil is being sent to the top of the engine quickly and will sit on top of the cylinder head. If the valve cover gaskets are leaking badly more oil will leak when going uphill.

[geezer#99]

And don't forget the intake to block mating surface. AKA the china wall. A known leaker if the gasket is installed wrong and has squished out.

['63GENIII]

Did you put the headers on? Did it do this before the headers were installed? IIRC, the oil pan dipstick tube on my 396 had to be pulled out of the oil pan every time I pulled the passenger side manifold. It was always a little loose after that. It didn't leak but it is awful close to the level of the oil and wouldn't take much to get some oil out of it if it was leaking that low.

[Marshy]

If you have a known leak on the pass valve cover and that is where the smoke is coming from then why are we having this conversation? Start with fixing the known leaks. You might be getting some oil from the breather hole in the valve cover or it could be a bad valve cover gasket, or it might even be a bad seal on the intake manifold gasket at the back of the engine. I don't think the trans fluid would work all the way up the tube and cause the smoke. GL

[storm9c1]

I agree with the others. Get a breather filter on the passenger side valve cover. Or run a hose to the bottom of the air filter. You shouldn't leave an open hole there! Oil can escape as well as dirty air can get in.

Secondly, I also agree that the trans won't blow out the dipstick unless it is overfilled and/or the vent in the top is clogged. The top of every trans has a small 1/4" or so sized hose attached to a nipple. This is the vent. As fluid heats, it needs room to expand and force out the air. Otherwise it will puke out the dipstick tube, especially if overfilled.

Let's discuss that too... How are you checking the fluid level in the trans? Truck warmed up after driving several miles? On a level surface, engine idling in park? Then check level on dipstick? If you did it any other way, that could be your problem.

[Dead Parrot]

Leaking valve cover gaskets can leak a lot of oil, think a quart every few hundred miles. It might smoke going uphill because the change in attitude causes the oil to hit the exhaust rather then the road.

+1 on the breather cap. No telling how many bugs are stuck in the oil pump screen.