# Engine Valve Cover Leak **URL:** \ **Category:** Factual Questions\ **Created:** [January 5, 2018, 11:50pm UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951 "2018-01-05T23:50:48Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![anomalous1](https://avatars.discourse-cdn.com/v4/letter/a/e56c9b/32.png) [@anomalous1](https://boards.straightdope.com/u/anomalous1)\ **Post date:** [January 5, 2018, 11:50pm UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/1 "2018-01-05T23:50:48Z")
On my 02 Cavalier (4 cyl) I noticed that the valve cover seeps a small amount of oil by the seams. Not enough to cause any significant loss between oil changes though. I am quite tired of taking it in to fix little issues. I already ordered the new gasket and materials, its quite simple to replace, and am doing so just out of fixing something that isn’t right, but my question is this; Can a leaky valve cover gasket cause compression or vacuum issues thereby hampering performance? Can air entering under the gasket seal (or lackthereof) cause a CEL (check engine light) or issues with any of the emissions control? Thanks everyone! ---
**Author:** ![Tired\_and\_Cranky](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@Tired\_and\_Cranky](https://boards.straightdope.com/u/Tired_and_Cranky)\ **Post date:** [January 6, 2018, 12:20am UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/2 "2018-01-06T00:20:05Z")
Certainly not compression issues. That would be caused by valve, head gasket, piston/ring problems, or cracked blocks or heads. I suppose the leaking valve cover could let unmetered air into the engine which could cause a lean burn condition and trip a check engine light. I had something similar happen when unmetered air entered my engine through a failed gasket in the oil fill tube. I’ve never actually heard of a leaking valve cover gasket actually tripping a check engine light though. ---
**Author:** ![Willcross](https://avatars.discourse-cdn.com/v4/letter/w/b2d939/32.png) [@Willcross](https://boards.straightdope.com/u/Willcross)\ **Post date:** [January 6, 2018, 1:12am UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/3 "2018-01-06T01:12:22Z")
If the valve cover gasket is leaking oil into the spark plug holes, the oil can contaminate the connection to the plug wires or coil and cause a misfire condition. ---
**Author:** ![SanDiegoTim](https://avatars.discourse-cdn.com/v4/letter/s/85e7bf/32.png) [@SanDiegoTim](https://boards.straightdope.com/u/SanDiegoTim)\ **Post date:** [January 6, 2018, 1:34am UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/4 "2018-01-06T01:34:14Z")
Assuming the valve cover is this sheet metal be careful not to overtighten. Doing so will distort it which will make a good seal impossible. ---
**Author:** ![JerrySTL](https://avatars.discourse-cdn.com/v4/letter/j/e274bd/32.png) [@JerrySTL](https://boards.straightdope.com/u/JerrySTL)\ **Post date:** [January 6, 2018, 2:01am UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/5 "2018-01-06T02:01:44Z")
No. Not likely. Willcross discusses about the only scenario that might cause a CEL. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [January 6, 2018, 2:22am UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/6 "2018-01-06T02:22:45Z")
If you haven’t done so recently, check the PCV valve. When one of those gets clogged, it can cause oil to start seeping out of just about everywhere on an engine. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [January 6, 2018, 4:31am UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/7 "2018-01-06T04:31:44Z")
> [@Willcross](#): > > If the valve cover gasket is leaking oil into the spark plug holes, the oil can contaminate the connection to the plug wires or coil and cause a misfire condition. I’ve never seen oil cause a misfire. It can cause plug wires and plug boots to swell, but it won’t affect their function. ---
**Author:** ![anomalous1](https://avatars.discourse-cdn.com/v4/letter/a/e56c9b/32.png) [@anomalous1](https://boards.straightdope.com/u/anomalous1)\ **Post date:** [January 6, 2018, 6:33am UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/8 "2018-01-06T06:33:02Z")
> [@gotpasswords](#): > > If you haven’t done so recently, check the PCV valve. When one of those gets clogged, it can cause oil to start seeping out of just about everywhere on an engine. Apparently I am either partially blind or this car doesn’t have a ‘standard’ PCV setup. All I can see that would be functionally similar is a short hose about 24mm in diameter connected to the intake resonator and the top of the valve cover. Can’t even find the parts for it on RockAuto… wtf. I suppose when I take the valve cover off to scrape and clean off and put a new gasket on I will check to see if that hose is clogged up… Any ideas? If this is it? Not really a pressing issue, but I like learning more. I found a picture of an 02 cavalier under hood; the middle upper of the picture, see that little hose? [https://images.duckduckgo.com/iu/?u=https%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fd%2Fd7%2FChevrolet\_Cavalier\_2.2\_L\_OHV.jpg&f=1](https://images.duckduckgo.com/iu/?u=https%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fd%2Fd7%2FChevrolet_Cavalier_2.2_L_OHV.jpg&f=1) ---
**Author:** ![anomalous1](https://avatars.discourse-cdn.com/v4/letter/a/e56c9b/32.png) [@anomalous1](https://boards.straightdope.com/u/anomalous1)\ **Post date:** [January 6, 2018, 6:42am UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/9 "2018-01-06T06:42:07Z")
> [@SanDiegoTim](#): > > Assuming the valve cover is this sheet metal be careful not to overtighten. Doing so will distort it which will make a good seal impossible. Its aluminum, not so worried about that, maybe have to be careful with the gasket scrape though :rolleyes: ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [January 6, 2018, 3:27pm UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/10 "2018-01-06T15:27:08Z")
> [@anomalous1](#): > > Apparently I am either partially blind or this car doesn’t have a ‘standard’ PCV setup. All I can see that would be functionally similar is a short hose about 24mm in diameter connected to the intake resonator and the top of the valve cover. Can’t even find the parts for it on RockAuto… wtf. I suppose when I take the valve cover off to scrape and clean off and put a new gasket on I will check to see if that hose is clogged up… Any ideas? If this is it? Not really a pressing issue, but I like learning more. > > I found a picture of an 02 cavalier under hood; the middle upper of the picture, see that little hose? > [https://images.duckduckgo.com/iu/?u=https%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fd%2Fd7%2FChevrolet\_Cavalier\_2.2\_L\_OHV.jpg&f=1](https://images.duckduckgo.com/iu/?u=https%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fd%2Fd7%2FChevrolet_Cavalier_2.2_L_OHV.jpg&f=1) no, that looks about standard. that little hose is upstream of the throttle so it’s actually the _breather_ hose; a source of fresh filtered air to regulate and maintain crankcase pressure. the actual PCV valve/hose is probably under the intake duct; it requires intake manifold vacuum to work and will be plumbed to somewhere _after_ the throttle body. edit to answer your other questions: > [@](#): > > Can a leaky valve cover gasket cause compression or vacuum issues thereby hampering performance? > > Can air entering under the gasket seal (or lackthereof) cause a CEL (check engine light) or issues with any of the emissions control? it’s possible, but it would have to be such a massive leak that you’d have oil all over the place. ---
**Author:** ![anomalous1](https://avatars.discourse-cdn.com/v4/letter/a/e56c9b/32.png) [@anomalous1](https://boards.straightdope.com/u/anomalous1)\ **Post date:** [January 7, 2018, 2:51am UTC](https://boards.straightdope.com/t/engine-valve-cover-leak/805951/11 "2018-01-07T02:51:30Z")
Thanks for the responses everyone! **jz78817** , I looked around and can’t find it for sh\*t. I keep reading this car as an oil/air separator in the valve cover and not a PCV (only models 1998 and below). I suppose I am going to check around more when the parts come and clean out the throttle body as well since I am going to be fiddling around and I am almost positive it has never been cleaned. Thanks!