Oil Fill Cap Removal no Longer Drops Idle

Andras Nagy · 07-25-2003, 04:09 AM

When removing my oil fill cap, the idle doesn't drop any more. And there seems to be smoke coming out of the oil fill tube when the engine is up to temperature.

What could be the reason?

Bill Verburg · Bill Verburg's Garage

Oil clogged breather

Andras Nagy · 07-25-2003, 06:51 AM

Could it also be something with the internals? Not that I'm looking for things wrong, but I will check this weekend and let you know.

But the smoking from the oil fill tube is bothering me, since it has never done that before.

Thanks.

jerrykrug · 07-25-2003, 07:29 AM

I was just going to ask a related question on the 993 board but now that the oil cap ?s are out there.....On My 1 year to me 96 993 I notice that the idle does not drop when the cap is open. Do the 3.6's idle drop as much as the older cars? and where should I start looking for vacuum leaks?

Thanks again

cmonref · 07-25-2003, 07:31 AM

Check the gasket inside the cap. The vacuum leak could be there.

Superman · 07-25-2003, 07:47 AM

Hi Andras.

Mine still drops, but not as much as it did before the engine overhaul. You can test the oil cap seal by removing the cap and placing your hand over the filler neck. Your hand would make a good seal. Idle should change.

Also, while you do this, notice how much vacuum is present. I believe that there is vacuum there, in spite of the connection between the filler neck and the crankcase. Crankcases make positive pressure, but that system is also connected to the air box, so I believe there should be negative pressure in the neck.

Purrybonker · 07-25-2003, 07:51 AM

My 3.2 behaves like Andras' car - the idle has never changed with filler cap removal and it usually belches a bit of smoke when openned. I have never thought that either of these things were noteworthy...

are they?

If so, why?

Superman · 07-25-2003, 11:25 AM

Oops. Forgot to offer my thoughts on the smoking thing. Oil smokes, so relax. Also, if the car is not driven often, like daily, then condensation gets in the oil and steam will boil off. That's the good news.

Engines, as they get older, experience 'blowby.' These are gasses that push past the rings and get into the crankcase. The crankcase makes air. Ugly air. To protect the spotted owls from these gasses, this air is plumbed back to the oil tank, where another line also connects this system with the air box. The air box is supposed to keep this system under negative pressure, drawing these gasses into the engine to be burned up. My suggestion to test the vacuum in the oil tank by using your hand, was also intended to cover this system. If there is a plug in the line between the PCV system and the air box, then the vacuum that's supposed to draw the gasses into the intake (and which also by the way causes your engine to stumble when you remove the oil cap), will not be there.