Thread: oil blowing out at high speeds

Tweet

I've had this problem for awhile ever since I put a more agressive cam(actually kind of mild 218/224 duration. >050). At speeds of 90 or higher my engine blows of pushes out oil from the oil filler tube or vent on my valve cleaner. I'm running a hose from my oil vent in my valve cover to my carb to take care of some blow by, but can't figure out how to fix this proble. My 305 is running a dual plane intake with a 600 cfm edelbrock carb. It's been bored .060 over with 10.1 pistons. The cam makes it idle pretty lumpy and I have a stock converter in place with my 350 tranny. My total timing is 36 degrees. Even with the high gears of 2:76, my 37 runs hard and it's pretty quick in the quarter at 103 with these gears, but after a run my engines is covered with oil.

.....hmmm, the 400 small block that I used to have in my '32 did this. So I'm interested in what others say about this. Everytime I'd get on it oil would be ALL over the place! I never really knew what the problem was as the motor blew up before I got it figured out {I'm not saying that's why the motor blew up}. Although when it did blow it broke the camshaft in half because of a bearing seezing so this could be an oil issue. I didn't have baffles in the valve covers so I put them in but it still did it {I tried two different types of baffles but still blew oil out}. Do you have baffles in the valve covers? Twice when I got on it the oil fill cap blew off & once the dip stick flew out! Someone told me it could be because the rings weren't seated so pressure was getting past the rings & into the oil pan. Then this pressure would release up to & out of the oil fill tubes. But what this was have with replacing a cam is beyond me.... Again, I'm interested in what others say..... good luck... Bill

Bill, Yes on the Baffles. I've tried two different types of valve covers and made my own baffles but that didn't solve the probelm.

Coming down a long grade on compression, does it smoke when you roll the throttle on far enough to maintain highway speed?
If so valve guides are probably worn.

If you roll the throttle on from low speed does it smoke and blow oil?
Rings are probably not sealing as well as they should.


If things look ok and you're on the highway, running 3000-3500 rpm (short gears) for a while, nail it and then smoke comes pouring out you have an oil vapor control problem.

You may even see a faint blue haze following the car while running at above normal rpm.


Aside from the above, this looks like it could be the problem: "I'm running a hose from my oil vent in my valve cover to my carb to take care of some blow by."

By oil 'vent' you mean PCV valve?

Or you're running a line from rocker cover oil filler cap to the PCV inlet bib on the carb thereby putting vacuum directly on the crankcase?

Or you're running a line from rocker cover oil filler cap to the air filter . . . and if so, does the line terminate inside the filtered area or inside the air filter, but not in the filtered area?

Take a look at this:

The line I'm running is not my pvc valve hookup , its on my other side on the engine and I'm using my vacuum from the carb to suck in blowbye which I never had until I put in the new cam. That took casre of blowby, and my valve guides are in good shape and the rings have seated OK as I'm not blowing any smoke out exhaust at any speeds. Take a look at the picture.

Which didn't come through. Let me try again.

Here's another picture

This one is from my PCV valve

If your pcv is working correctly,your other hose should be letting fresh air into the engine. Changing cams can giveyou more cylinder filling,increasing the chance of blowby pressurizing the crankcase. You could test for this by hooking a vacuum/fuel pump pressure gauge to your breather cap and going for a ride. How much manifold vacuum did you lose from the cam swap? Hank

Does the hose on the right side go into the bottom of the breather? If so wont your pvc line on the left, and the hose on the right be fighting against each other. And you cant have a channel of air flowing through that way can you? Ive always thought one had to be vented to let air in and the other was set to a vacume port to draw the air through. I dont know I am just asking.

i have seen were a pvc valve will not work good with big cams no vac to work it and any foam filled beather get oil filled and stop working the higher the beathers set off the valve covers the better they work and keep them away from oil splash

Hank I have a manifold pressure gauge always hook up to my engine and I run 15 lbs. at idle and 25 a full throttle.

Mooneye 777 the pcv valve vents the crankcase of excessive pressure into intake manifold or intake system. What I'm doing is taking the blowbye that the pcv valve is not taking all of and using the vacuum from the carb or intake to drawn the fumes into the carb and burn it off. I really don't know if this is harming the engine or not but there is no more blowby at high speeds, just oil blowing past the dipstick or oil cap on the valve cover. Maybe to much pressure is causing this but it just happened when changing cams, and the cam is not a aggressive one.

Pat. I'm using the highest breather cap I can find. I even made my own that was 4 " tall, but it still didn't work. The cam specs are 262-270 adv. dur Int/Exh. 218/225 Dur.050 Int./Exh. Lift int./exh. .462-.469 lobe seperation 110 degree.

well them MR gaskets are junk they have foam in them when they get wet with oil they never stop blowing oil out try making some thing like this

Nice looking engine. Did you make the breather cap from stainless tube and retrofit something for the breather itself?