When I get up to about 4500 rpm the dipstick lets a couple of drops of oil spill out onto exhaust. I have breathers on the valve covers. What could be causing this?

 

you should have a pcv in one valve cover. not a breather in both

 

You have breathers plural? So no PCV Valve? Also, sounds like possibly blow-by.

 

Building positive pressure in the crank case, need to fix/re-install a working PCV system, the crank case should be under vacuum if I'm not mistaken.

 

Yup, only run no pcv valve if you want to kill your engine.

 

Please explain. How will no PCV kill an engine?

PCV was first used in the 60s as a safety measure to prevent build up of combustion gases in the crankcase(explosion?) and to reduce smoke and odor. It was then adopted as an emissions device to prevent release of these same combustion gases into the atmosphere. Before that time, no engine had PCV. Earlier engines all simply vented the crankcase to atmosphere.

Aside from the minor risk of explosive gas build up, there is no functional need for PCV on an engine. It only produces vacuum in the crankcase at closed throttle anyway. Under load, there is little or no vacuum and crankcase pressure is released into the inlet air tract, same as it would be released to atmosphere through a vented breather. Race engines don't use PCV because they produce too much crankcase pressure and have to be vented, either by breathers, or by vacuum evacuation(vacuum pump).

If your dipstick is being pushed out due to crankcase pressure overcoming the breathers, you have a serious blowby problem. It's hard for me to even imagine that much blowby on any engine that starts and runs. It would almost have to be rolling smoke out the tail pipe. Unless somehow the path to the breathers is restricted.

Have the valve covers been off recently? You may want to pull them and look for heavy sludge build up. You can check the VC vent openings by pulling the breathers and feeling for flow as you snap the throttle. The breather caps also need to be cleaned now and then. Aerosol brake cleaner works well for this. Let them dry thoroughly before reinstalling them.

Otherwise, are you sure your oil isn't overfull? Any factory stock SBC V8(aside from some vettes) holds 5 quarts.

 

Ugh, there doesn't need to be another thread on here about pcv does there? Pcv doesn't really do squat for emissions, it takes the gases that turn turn your oil into a toxic acidic soup. The gases then get sucked into your intake and burned off. Older cars have draft tubes, race cars don't go 3+ k miles between oil changes.

 

Yes, he could have a clogged breather, gunky oil, and clogged breather caps. He should be running a PCV valve though, it doesnt hurt anything and many people would say it is not very good not to.

 

One other thought is that you are running the oil too high in the case and the piston skirts are actually acting as a pump to over pressurize the pan and generate bubble is the oil. Is your dip stick original for that engine? Excess oil level can also lead to blown seals.
The dip stick tube need to have sealant where it goes into the block.

 

I had to laugh. i built the current 350 in my iroc over 10 years ago, beat the dog snot out of it, 100 shot, and just 2 breathers with no PCV. i havent used a PCV on any of my builds over the years because i believe it to help foul plugs quicker, JMO. but to say not using a PCV will kill your engine is just not true.

 

I had that problem years ago. I got a spark plug boot from a BBC plug wire set. It's long and straight. I slipped it over the dipstick and now when I put the dipstick into the tube, the boot seals it up. I suppose a piece of rubber hose could just just as well.

My engine now has a belt driven vacuum pump for the crankcase so the boot just helps it seal even better.

 

It won't necessarily. For those who don't do oil changes when they should it can damage the engine more than usual. You have to realize most people don't keep up with their maintenance anyways.

 

A small percentage of early cars(pre PCV) had draft tubes to direct crankcase vapors away from the underhood, where they would be more likely to be drawn into the passenger compartment. Most didn't have draft tubes. The all original (museum piece) 57 Chrysler 300C sitting in my bay right now has a breather cap, no draft tube.

The acid soup is created by exposure to sulfuric acid. This occurs with combustion and PCV makes very little difference. Almost any decent oil today will hold up for at least 7K miles before the acid starts to break it down. The one real benefit I see with PCV is drawing moisture from the crankcase that accumulates with heating and cooling metal, especially in moist climates. A decent run down the highway, getting the motor good and warm, does just as well at drying things out.

If you think PCV is useless as an emissions device, you might want to let the EPA know. They require PCV on every applicable vehicle. You will fail any strict underhood emissions inspection for having it disconnected.
Anytime I am diagnosing a fuel trim issue, whether it's on a carbed or EFI engine, the first thing I do is pull the PCV valve out of the valve cover and lay it to the side. When I see the CO or fuel trims correct, I know I'm looking at fuel contaminated oil, which is common on vehicles that go long on oil changes.

I have had several of my own SBC builds that the owners ran without PCV run many years and over 100K miles with no mechanical failure.

EDIT: I do not mean to advocate for going 7K miles on an oil change. Only that today's leading oils will hold up for that long. The oil will be nasty with carbon particles and abrasive compounds long before that. Please do change your oil atleast every 3K miles. More often if you drive hard.

 

You should have seen my parents '60 Falcon with road-draft tube...puffing away like the stack on a coal powered steam engine. And yes, you inhaled a bunch of that going down the road.

 

I have never measured the difference. But, I would imagine that due to the amount of HC that ends up in your crankcase vapors, having a PCV connected on a closed loop EFI system must certainly gain you some amount of gas mileage improvement, and visa versa.

 

I'm not saying that a freshly rebuilt engine will die from not having a pcv system. The OP has an engine of uncertain background in his car. Probably around 30 years old with unknown mileage and upkeep history, and is spewing out enough air to push up the dipstick. If he took off the intake, dropped the oil pain and removed the valve covers, it'd probably look pretty nasty in there. Because of the possible history of his engine, probably having been driven 10k miles between oil changes at least once, with probably the crappiest conventional oil imaginable, and god knows what else. He should be running with PCV as it would help his engine in his instance last longer. He should also be doing regular oil changes with a good oil to try to get some of that crap out of it.

 

We should go back to the old 30's Chevy or Model A. Use to go down to Sears and buy Rejuvenated oil when it got low. Kind of changed itself. Clearances were so big, sludge didn't matter. So we had to hand pour and scrape in new rod bearing every now and then, but they ran for 500,000 miles or so, most on dirt roads. Now we got to pay $8 a quart for fancy synthetic.
Progress?
Only foolin' with ya.

 

Agreed.

 

LOL.

 

Anyone use a breather having a one-way check valve?

I'm running an open-air element so I plugged the vacuum line going to the TBI and installed a breather on the passenger-side valve cover. It doesn't have a one-way check valve and sounds like I should.

Anyone have a part number for what they're using?

 

You do not want any check valve on a crankcase breather.

By the line going to the TBI, do you mean you plugged the PCV hose? If you are deleting PCV, you need to be sure you have ample ventilation. In that case, I would suggest a breather on both valve covers.

On a stock, or close to stock application, there is no benefit and the possible hazards discussed in this thread, to not having functional PCV. As far as a check valve goes, PCV valve acts as a vacuum regulator allowing only so much flow through the PCV line from the valve cover to the manifold vacuum connection at the TBI. It also serves as a check valve, also known as an anti backfire valve, in the case of a sudden pressure pulse from the intake side. Running an open air cleaner makes no difference in this part of the system.

The make up air side will change, since you have deleted the factory make up air connection. You can replace the make up side of the system by installing a breather at the valve cover. In normal operation, the PCV make up air side draws vapors from the crankcase through the throttle body when the throttle is opened wide under acceleration. With a breather in the valve cover and an open air cleaner, you lose this function, but you still have positive ventilation through the PCV valve under all other operating conditions.

 

Sorry, my post wasn't very clear.

The PCV valve is still connected on the driver's side. I didn't mess with that at all. The vacuum line I plugged off is what was previously connected to the vacuum plenum. On the passenger side valve cover I have the breather plugged in, which replaces the hose that originally went straight into the air cleaner. Sorry I can't post pictures since I'm storing it in another state.