So if you drive without an oil filler cap....

[Figit090]

What does it do? I'm guessing that a properly sealed engine is supposed to develop a vacuum inside it and that's what creates the vacuum for the rest of the components that need it...am I right? I dont know anything about this aside from speculations made from experience.

Either way, my question starts when...a friend drove her ford explorer about 15 miles or more without an oil cap, and once the inevitable car trouble happened we stopped and I had a look. I discovered the missing oil cap. Apparently the last to check the oil/add some left it off on accident. Then I checked the oil, and it wasn't hardly on the stick. (oh man..)

I look under the car and see lots of oil...and then look around to find the source... It was seeping from the airbox! :aigo:
The truck ended up spitting lots of it's oil supply out through the air intake, with just a little splashing out of the oil filler hole at the top of the engine.

What caused the oil to go out the intake?

Sadly it was late at night and they more or less had to drive the truck home 10 miles or so without a new air filter, so it stalled trying to pull up a hill, but at least they got it most of the way home. I am only hoping that the low amount of oil left in the engine didn't damage anything... At the very least I think the only *damage* that's obvious is a most likely saturated air filter...:biglaugh: hopefully that's it.

 

[zachm611]

some cars running without the cap will spit out oil out from the filler hole i guess you can call it. it makes a huge mess too. PITA to clean up.

 

[Facime]

yep, driving with the cap off is what caused the oil in the intake. I dont know what if any long term effects that would have though.

 

[Figit090]

thanks Weezl. how did it happen though? valve stem seals spewing oil? maybe an intake-fed crankcase vent? I'm just trying to figure out how that would have happened. It's a new concept to me...lol.

zachm611 - it wasn't just the filler cap, in fact most of it DIDN'T come from there, only timing-chain splatter. It was all OVER the bottom half of the intake box and it made a puddle on the other side of the engine.

 

[Facime]

think PCV system. With the cap off you dont develop the positive ventilation out the system as designed. So the oil basically blows out where it wants.

 

[johnathan1]

I accidentaly left the oil filler cap off of my Mercedes (inline 6) and it just splashed a little oil onto the valve cover...drove it for 25 miles like that with no ill affects. A bit of a DOH! moment tho lol.

 

[BorHor]

I did that once in the supra.. Drove to Sac and back (120 miles each way), I opened the hood when I got home and saw see what an idiot I am.

 

[annoyingrob]

yeah, I drove about 300km with the oil cap off. lol. Nothing happened.

I ahve NO idea why it would end up in the intake though.

 

[boosted1jz]

you could get dirt in the engine.... thats what

 

[MKIIINA]

my dad wanted to do me a favor and check my oil, he forgot to replace the oil cap. Luckily there was a fellow car enthusiast at the gas station I stopped at to top off on gas! what was only 10 miles could have easily turned into 200.

Add oil, clean off the engine (oil could start a fire) and replace the air filter

 

[RazoE]

kinda related:

my dad once poured oil into my 240sx with the engine running, and it all spewed out and splatted in the bay...

 

[Figit090]

think PCV system. With the cap off you dont develop the positive ventilation out the system as designed. So the oil basically blows out where it wants.

oh ok

I did this once on my supra with no ill-effects. might have if i had driven it more but i'm not sure. i know it will idle like crap without the cap.

The ford explorer didn't like it though! lol.

thanks for the input guys!

 

[Zumtizzle]

kinda related:

my dad once poured oil into my 240sx with the engine running, and it all spewed out and splatted in the bay...

:rofl: :rofl:

 

[IwantMKIII]

Its extremely messy. Pull it off at night time, let the engine warm up and put a light in the engine bay so you can see whats really all coming out of it. Its nasty.

 

[Quin]

I dunno about oil starting fires, I have about 7 gallons all along the bottom half of my block, half the shit in my engine bay and my entire underbody/drivetrain, hasn't caught on fire yet! :nono: lol

 

[flight doc89]

if i understand it correctly(remember, I'm Stoopid), the PCV system dumps the gases building up in the crankcase into the intake so that the fumes get burned. somehow leaving the cap off made oil go through instead of fumes?

 

[OfnaRcR4]

you could get dirt in the engine.... Thats what

dingdingding!

 

[gaboonviper85]

if i understand it correctly(remember, I'm Stoopid), the PCV system dumps the gases building up in the crankcase into the intake so that the fumes get burned. somehow leaving the cap off made oil go through instead of fumes?

not quite....the block is somewhat sealed....so the crankcase can only ventilate so much...the only air/gas comeing in the motor should only be the gases that seep past the piston rings....BUT...with the oil cap off you now have a HUGE FUCKIN HOLE in the motor that lets more air in makeing the pcv system able to breath 20,000 times better meaning it sucks in alot more oil mist/fog and exhaust gasses.....

think of it like a water bong.....while you are lighting it you really dont get a good hit....but once you pull the stem out all the sudden all that fog gets cleared and you cough up a lung!

 

[Figit090]

haha, nice analogy.

makes sense. So I googled that the PCV system is the Positive Crankcase Vent, and now it all makes sense. I had not really known what it was before this.

OH!!! Is that what the vent pipes are for on top of the head covers!? the two that T-off and go into the intake?

I've seen them on small engines and wondered what they are for exactly, now I know!

haha... that would be a really sad way to loose an engine.. leave the oil cap off, have it spit out all the oil, and burn up. all because of a little cap.

 

[Tanya]

Drove from South Carolina to New York with no oil cap. Dunno if my engine had a BHG or blown seal, but it was pissing oil BADLY and we had no time/money to fix it. Ex accidentally left oil cap off at one of our fillups and the oil consumption slowed down GREATLY, so we just kept it off.