Engine oil cap is very loose

[OilUzer]

We have one car and the oil cap turns very loosely maybe 3/4 of a turn and doesn't lock. After closing it, I can lift it up and down about 1/4" and seems to be loose and have lots of play.

We owned the car since new (2005). None of our other cars (from 97 to 2016) do this. They all close/seal very tight ...

This car doesn't lose or burn any oil. I just changed the oil after 5K miles (10W30 Chevron Supreme out, 5W30 CS in) oil color was still good and I may have added 8-10 fl. oz. Max during the 5000 miles.
Anyways, the cap stays on (still the factory cap). However I am wondering if it is defeating the pcv system and allowing oil vapors to escape! What's up with this design? Car is a v6 mpfi, over 200K miles and has pcv system, etc.

 

[Mad_Hatter]

It wouldn't effect combustion chamber pressure and whether gasses get vented into atmo via a loose cap or via PCV, it not an issue per se unless you take into consideration the air we breathe and/or you'll miss burning some of those gasses in the combustion chamber. Some folks even install (you can drill a hole into the non-pcv valve cover of V6's and 8's) breathers👇 to keep crankcase pressure and gasses to a minimum.

 

[OilUzer]

To be clear, we bought the car new from dealer and no one has messed with it. i.e. it's all factory stuff!

 

[Mad_Hatter]

Originally Posted by OilUzer
To be clear, we bought the car new from dealer and no one has messed with it. i.e. it's all factory stuff!

Buy a new cap if it troubles you, or if it's under warranty ask the dealership to replace it. All I'm saying is it's not gonna effect the engine performance wise, not at least in any way I can see.. unless I'm missing something here??? You could run your engine without a cap as far as I know.. it'd be messy but you could do it. (it's not a pressurized system like the cooling system)

 

[FordBroncoVWJeta]

Originally Posted by OilUzer
To be clear, we bought the car new from dealer and no one has messed with it. i.e. it's all factory stuff!

So why not complain in 2005?

 

[OilUzer]

Originally Posted by FordBroncoVWJeta
Originally Posted by OilUzer
To be clear, we bought the car new from dealer and no one has messed with it. i.e. it's all factory stuff!

So why not complain in 2005?


Not complaining and not concerned about the performance either @Mad_Hatter ...

Just changed the oil on Saturday and got curious again about this design ... did some googling but didn't find any info and posted here.
kind of curious if oil vapors and mist can escape and if anyone else has seen this design!

 

[CharBaby]

What type of cap is it?...screw on OR push in & 1/4 turn, OR???
Did it lose its gasket/seal?
Can you mod it to make it tight(er)?

Be creative. This is what separates us BITOGers from the rest.

Best of luck,

CB

 

[Mad_Hatter]

You're gonna have some gasses escape via loose fit.. I'd imagine over time it would contribute to engine bay dirtiness??

 

[OilUzer]

it's a screw on and the car has been to dealer for oil changes several times and they never said the cap is bad! It's been always like that and that's why I thought it is per design. Maybe it was bad since new and why mess with it after 200K+ miles

there is no visible oil near the cap surface either! Last time I changed the pcv valve, it was dirty so that path is still functional.

Hypothetically speaking, if you leave the oil cap off and/or if it is very loose, the pcv valve should stay very clean. No?

 

[bbhero]

Try leaving your cap off...

And then see if it is louder than normal... Or if it is still the same. I am the World Champion who did that feat about 4 months ago... And it was not on purpose. Forgot to put the darn thing back on after adding just a bit of oil to my car. I was rather surprised it was no real noticeable difference which was interesting. The car did not go anywhere when this happened. I noticed the cap off right has I was closing the hood.

 

[MParr]

We don't know what kind of car it is. We don't know if the car was designed that way. We don't know if it has a defective oil filler cap. Get a new cap and see if it helps. If not, you have a spare cap.

 

[joekingcorvette]

Yes, it looks like it's time to buy a $10 cap.

 

[Fawteen]

You've owned the car since 2005 and now almost two decades and 200,000 miles later there hasn't been a problem with the cap, it just seems ever so slightly "loose" and has been that way since it was new. In all that time there has been no evidence of anything leaking, no "mist", no pvc issues, no other sign that this is a problem other than it seems a little loose. Is that correct?

It doesn't sound like an issue.

 

[bullwinkle]

If your PCV system is working correctly with minimal blowby, you're sucking dirt into the crankcase via the loose cap, time for a new one.

 

[Trav]

Its not the oil vapors escaping, the concern would be unfiltered air being drawn into the crankcase instead of from the PCV system. Get a new cap.

Edit: I see bullwinkle had the same thought.

 

[Mad_Hatter]

Originally Posted by bullwinkle
If your PCV system is working correctly with minimal blowby, you're sucking dirt into the crankcase via the loose cap, time for a new one.

Good point. ðŸ‘..i didn't consider that it could be a point of contaminant ingress.

 

[MasterSolenoid]

Originally Posted by Trav
Its not the oil vapors escaping, the concern would be unfiltered air being drawn into the crankcase instead of from the PCV system. Get a new cap.

Edit: I see bullwinkle had the same thought.

My thoughts exactly.
When you get the 'new' cap, assuming that it will be snug, compare it to the original and see what the difference is.

My under the hood exam always includes loose air hoses 'after' the Air Cleaner.

If you start the engine and remove the Oil-Fill-Cap, put a piece of paper over the opening and you should feel a slight vacuum (suction).

 

[WyrTwister]

Off the top of my head , is a gasket missing / lost ?

Is it loose enough that air is being sucked into the engine , past the oil cap .

I found out , when changing oil / filter on our 2015 Sonic 1.8l , if I did not re-install the cap , when I started the engine to fill up the filter , before topping off the oil ( from a 5 quart jug ) . It essentially produced a huge vacuum leak and the engine ran poorly .

With the oil cap in place , the engine ran / runs normal .

 

[PimTac]

Sounds like the cap got swapped out at some point.

Why it took all this long for you to figure this is another question.

It ain't right. Get it fixed.

 

[Ursatdx]

Originally Posted by WyrTwister
Off the top of my head , is a gasket missing / lost ?

Is it loose enough that air is being sucked into the engine , past the oil cap .

I found out , when changing oil / filter on our 2015 Sonic 1.8l , if I did not re-install the cap , when I started the engine to fill up the filter , before topping off the oil ( from a 5 quart jug ) . It essentially produced a huge vacuum leak and the engine ran poorly .

With the oil cap in place , the engine ran / runs normal .


I'd bet the OEM gasket is missing or a different cap is in place.
Either way, I'd repair/replace it.