Driving car without breather cap

[Ray70Chrg]

Just as a test, I'm wondering if the car can be driven without the breather cap installed and not make a big mess in the engine compartment. This is a 383 magnum with original valve covers and the area below the cap is baffled. The pcv will be working as usual. I just want to see if the breather cap is not suppling enough air to the crankcase when driving at highway speeds. I seem to getting a small leak at the back of the engine on high speeds but during street driving it's not leaking. The rear main seal was replaced recently and appeared to be successful until I got it on the highway. The oil pan gasket has also been replaced and solved the problem of leaking at the front right corner. The valve cover gaskets were just replaced and torqued to spec. I've had this car for 5 1/2 years and been chasing oil leaks from everywhere. I thought I had it finally fixed until I went on the the highway. Hope I'm chasing a pressure type leak this time.

 

[Nevada dan]

your not serious, take a picture when your done for us

 

[Ray70Chrg]

I'm asking a question! If you don't have a answer, keep your sarcasm to yourself. Thanks for nothing.

 

[R413]

It depends on the engine condition and how far down the gas pedal goes. When floored the manifold vacuum is nill and the PCV does nothing

It will likely have some oil come out. You will have to try it and see how much.

 

[Nevada dan]

sorry bout that

 

[Ray70Chrg]

Hey R413, thanks for replying. The breather cap doesn't have any oil in it now. It's relatively new, maybe 800 miles old. The way I understand crankcase ventilation is the breather cap supplies air into the crankcase and pcv evacuates the built up gases via the manifold vacuum. Since the valve cover is baffled under the breather cap, little to no oil comes to the breather cap under proper operation. I'm just wondering if this can be done and not create a mess. Thanks.

 

[toolmanmike]

Hey R413, thanks for replying. The breather cap doesn't have any oil in it now. It's relatively new, maybe 800 miles old. The way I understand crankcase ventilation is the breather cap supplies air into the crankcase and pcv evacuates the built up gases via the manifold vacuum. Since the valve cover is baffled under the breather cap, little to no oil comes to the breather cap under proper operation. I'm just wondering if this can be done and not create a mess. Thanks.

Sure. If it does make a little mess you clean it up and go on with your diagnosis.

 

[Tony Tee]

I'm guessing at idle, with a working pcv valve and a healthy engine. The vacuum should suck in air at the oil leak area. If the engine has excessive (blow by), the pcv valve can't keep up and would would leak oil at the leak area due to positive crankcase pressure. Just guessing. Or,
You could pressurize the engine when it's not running through the pcv hose to 5 psi with compressed air and listen for a air leak? But be careful. You might cause more oil leaks this way.or bulge out your oil or valley pan. Again just guessing.
I pressurized my cooling system this way to find my coolant leak. Because it would only leak when driven. Worked great!

 

[74gtx]

Does your dipstick pop out after spirited driving?

 

[wagonman]

In a perfect world you would have no positive crankcase pressure. Maybe rig up a vaccum/ pressure gauge to the breather grommet and see what you have when running hard. The factory breather was vented to the air cleaner, is that what you have? My push in breathers weep a little on long runs.

 

[Ranger16]

I'm not sure just how you plan on testing the cap on the highway. You should be able to just run up the RPM in the garage and watch it. Shut down if it starts creating a mess (which I doubt).

I'd also doubt that the breather cap is restrictive if you are using something like this.

 

[Ray70Chrg]

Does your dipstick pop out after spirited driving?

No, dipstick is not popping up. A few weeks ago I did notice that a few puffs of smoke came out of breather cap after start-up. I read thru some of the threads here and they directed me toward the pcv not working properly. I replaced pcv and have not seen that since.

 

[493 Mike]

A piece of writing paper should stick to the breather grommet at idle if the PVC valve is working properly (assuming the engine is sealed).
Mike

 

[Ray70Chrg]

I'm not sure just how you plan on testing the cap on the highway. You should be able to just run up the RPM in the garage and watch it. Shut down if it starts creating a mess (which I doubt).

I'd also doubt that the breather cap is restrictive if you are using something like this.​

View attachment 1121717​

The one I'm using has a hose connection to the bottom of the air filter housing. I don't use the original housing anymore, use a Edelbrock instead with no hose connected. The diameter of the hose fitting is 1/2" while the bottom opening of the breather is 1". The one you show above seems to have a combined area that's much greater than 1/2". It was the hose nipple fitting that made me think the breather cap was being restrictive at highway speeds, 65-70mph. Thanks for the tip, I'll certainly try that kind of breather.​

 

[Darter6]

Please take this in jest,, Old saying "It ain't a Mopar if it don't leak"

 

[Ray70Chrg]

Please take this in jest,, Old saying "It ain't a Mopar if it don't leak"

Having owned several mopars in the last 5 decades, I know that saying holds a lot of truth. One of my many faults is trying to be a perfectionist in a imperfect world. Compound that with 51 year old cars and tons of revisions and it all = Perfect Frustration.

 

[diesel_lv]

Please take this in jest,, Old saying "It ain't a Mopar if it don't leak"

If you don't see oil on the ground, don't start it, it's empty.

 

[Ray70Chrg]

A piece of writing paper should stick to the breather grommet at idle if the PVC valve is working properly (assuming the engine is sealed).
Mike

With breather cap removed, I started car and put a piece of paper over the breather hole and a slight suction held it in place. Thanks for the tip on that test.

 

[eldubb440]

A piece of writing paper should stick to the breather grommet at idle if the PVC valve is working properly (assuming the engine is sealed).
Mike

I call it the dollar bill test