Could you help me with this????

[strat1960s]

Those of you with healthy motors, could you run your motor until it has reached operating temperature. With the motor running, could you pull off the oil filler cap/breather and check to see if you have pressure or vacuum.
Here's the deal. I found a shop that came highly recommended and they told me that there was vacuum at the filler opening. They are under the impression that there sould not be a vacuum there, but instead there should be slight pressure. The technician told me that when the rings are not seated it will create a vacuum inside the valve cover.

Please let me know......

Ted

 

[addo]

That is really weird. I'm neither accepting nor disputing it. It would be great if the fellow would flesh out his reasons a little.

One of the '60s diagnostic tools here was made by AC and it came as a generic crankcase pressure tester. A bit like the vacuum/pressure gauges you can buy. A rubber bung filled the dipstick hole and also the PCV/draught tube. With your motor at operating temp, you then attached an oil cap adaptor which led to the gauge. The amount of pressure (blow-by) was read as engine wear.

That's what I was "raised" on, but I am equally receptive to superior and more modern ideas about these things!

Regards, Adam.

 

[MustangSix]

I have always noted a bit of vacuum on a healthy engine at idle. I could pull the breather cap off and no fumes escape, and you can get a slip of paper to suck up against the opening.

 

[addo]

Isn't that vacuum from the PCV, though? I understood Ted was talking about with the PCV plugged.

 

[strat1960s]

Ok,

I checked it out today and it sucks so much that when you pull your hand away, it sticks a little and makes a sucking sound. Is it possible that there is so much vacuum inside the valve cover that it is not letting the PCV do it's thing? If you crimp the PCV hose it affects the RPM.

Also, My breather has a hose on it that I assumed connected to the air filter housing. If there is a vacuum being drawn in to the breather, would this affect the air going in to my carb? Could it be sucking the air out from inside the air cleaner and carb?

Ted

 

[PLP6400]

I had vacuum at my oil filler untill I changed my PCV valve. I don't run the hose from the filler cap to the air cleaner because I have Ram Air and I figured at freeway speeds I might slightly pressurize the engine. So I just have a ventilated filler cap.

 

[Anonymous]

If I remember a slight vaccume is good and pressure is bad. The lower the pressure in the crankcase the easier it is for the piston to move under power. Wouldn't pressure cause problems like blowing out seals and gaskets?

 

[80broncoman]

Ok my 300 is more of a 5cyl due to a burnt exh valve. so I won't even thick of trying this on it. I will get to it this spring I swear.
But I noticed somthing very odd bout my CRV a couple of weeks ago.
I pulled the pcv valve out of the cover at a Idle and noticed the crankcase was pressureized I could not belive it , but just as soon as I open the throttle it goes to a vacume. It has 122k miles and uses a quart of oil in about 2000 miles and does not smoke. It runs great. I don't have a clue but I'm not about to tear it apart.
Jim

 

[strat1960s]

What color does trany oil smoke look like when it is burned inside the motor????
I say this because the trany fluid level has droped just a little. When I checked the vacuum modulator hose a while back it looked clean and dry. I'll take a closer look at my trans pan, output seal and bell housing to see if it is get out through there. I think I may have found my leak..... or at least one of them. Since I drove the car on the highway yesterday and today I haven't lost any motor oil. If the car is a little hard to start and I get on the gas as I am cranking it really smokes up a storm. Again, I am thinking vacuum modulator because when I have to get on the gas and romp on it to keep it running, I would imagine it's really pulling a huge vacuum on the modulator.

I'll keep ya'll posted on what I find out.

Ted

 

[turbocharged66stang]

hey turbocharged66stang hear and i own and operate a mechanic shop and can tell you that a vacuum is a good thing if their is a pressure than one of two things are wrong ether your PVC valve is plugged or your rings are not even close to sealing. so whoever you took your car to ether dont have a clue or he is just trying to get your money. if you have any more ?s e-mail me at partschangers@netzero.net good luck
TURBOCHARGED66STANG

 

[strat1960s]

Well, the two guys that looked my car over hadn't seen an in-line 6 in years so it is possible they forgot or didn't know. The shop that built my motor told me that there should be a vacuum at the oil filler hole. Here is another question. Should that vacuum be constant or should it come and go?

I really wish I could figure this thing out. I mean the smoking has gotten worse since I had it on the highway this last weekend. It's kind of frustrating.

Ted

 

[JOHN G]

As turbocharged66stang correctly identified-vac is a good thing. Some other persuasions of engines won't even run with the oil cap removed because of the vac loss! Bad valves will create pressure in the cover.

 

[LameHoof65]

I don't know much, but I do remember my dad telling me that if I put my hand over the breather and pulled my hand off and it didn't suck, then the engine is most likely in need of a ring job at the very least---but then he was a FORD quy from birth and so were his brothers----and none of them lived to see the later technology and advances we have today, so maybe things are different for the newer model engines. :

 

[mikeyo]

Hi,
I hate to argue with a recommened shop, but I have out mechaniced(is that a word?) a few of them.
My experience and way of thinking is that pressure or air blowing out of a valve cover breather is a problem caused by leaky piston rings. With good tight rings blowby is minimal and results in a fairly neutral crankcase pressure. High negative can be caused by worn intake valve guides. A very, very slight negative or positive pressure is of no concern, I have used a light piece of paper, like cigaretter paper, holding over an open valve cover breather hole to determine air movement. If you can feel anything strong (or worse yet hear it) by hand it has been my experience something isn't right in the engine.
Hope a long time 'shade tree' guy can help. lol.