A cheap gasket that gets expensive if you wait.
Oil seeping past a valve cover has somewhere to go. Down onto a hot exhaust manifold it smokes and smells. Down into the spark plug wells it drowns coils one at a time. The gasket itself is a modest part. What it damages while you drive on it is not.
- Open 24 hours, seven days
- No hourly minimum
- Licensed and insured
- Done where the vehicle is parked
The burning smell people call electrical
A customer describes it the same way almost every time. Something smells like it is burning, it is worst after a longer drive, it fades when the engine cools, and it smells vaguely electrical, so the worry is wiring. Nine times out of ten there is nothing wrong with the wiring. Oil is dripping out from under the edge of the valve cover onto the exhaust manifold, which runs several hundred degrees, and it is cooking off. That is the smell.
The reason it fools people is the timing. Nothing happens at idle in a cold driveway, because the manifold has not come up to temperature and the oil has not thinned enough to weep. Drive to Fairfield and back, park, and the smell arrives through the vents while the car sits there ticking. Some drivers see a wisp of smoke from the back of the hood at a stop light and assume the worst.
It is worth taking seriously for a reason that has nothing to do with the smell. Oil on a hot manifold is a fire risk on an older engine with a heavy leak, particularly once it has soaked into heat shielding or the insulation on a nearby harness. Most leaks never get there. The ones that do got there by being ignored for a year, which is the only real argument for not putting this one off.
There is a quieter version of the same failure that produces no smell at all. If the leak is on the inboard side of the cover rather than the outer edge, the oil never reaches the manifold. It runs down into the spark plug wells instead, where nobody looks, and the first sign anything is wrong is a misfire months later.
What gives it awayA hot burning smell after driving, oil crust down one side of the engine, a small puddle on the manifold shield, or a misfire that arrived without warning.
The figureWhat the job runs is settled on the phone once we know the engine, and a short job stays a short job because nothing is padded up to a minimum.
Where this happensDriveways, work lots and street parking across Napa and Solano, plus regular runs over the Carquinez. See the counties we cover.
Oil in the plug wells is the expensive part
Most modern engines sit the ignition coil down inside a deep well, directly on top of the spark plug, and the valve cover gasket is what keeps oil out of that well. When the seal around each well hardens and shrinks, oil fills the hole and the coil ends up sitting in it. Coils are not built to live in oil. The boot swells, the insulation softens, voltage starts finding a path to ground it was never meant to take, and the cylinder misfires.
The part people find frustrating is the sequence. A coil gets replaced, the misfire goes away, and everyone is satisfied. Six weeks later a different cylinder starts doing it, because every coil on that bank is sitting in the same oil. Replaced one at a time, a gasket job turns into a coil job several times over, and the original leak is still there doing the same thing to the new parts.
So when we pull a cover and find oil in the wells, we say so before the gasket goes on, and we deal with what the oil already ruined in the same visit. Wells get cleaned out properly rather than mopped at. A coil boot that has gone soft gets replaced. A plug that has been standing in oil comes out. Doing that at the same time costs far less than a second visit, because the cover is already off and that is most of the work.
Anybody can bolt a cover back down. The job is knowing what the leak already damaged underneath it and telling you before you pay for the same repair twice.
Patrick Freeman, owner
Two things the cover itself can do
A gasket is not always the only part that needs to leave. Two failures sit one layer further in, and both change what the job costs.
A warped cover will leak again
Aluminum covers warp, usually around the bolt holes, because somebody before you overtightened them. The metal pulls up into a shallow dome between fasteners and the new gasket cannot bridge the gap. We lay a straightedge across the sealing face before anything goes back on. If it rocks, a fresh gasket is a wasted afternoon and the cover has to be replaced or resurfaced.
Plastic covers are often one-time parts
Plenty of newer engines use a molded plastic cover with the gasket bonded into a groove, and on some of those the gasket is not sold separately at all. The plastic also goes brittle with heat cycling, so the bolt bosses crack and the flange distorts. When a cover is at that stage the honest answer is that the whole cover is the part, and you hear that when we look, not after.
Plugs and coils
What comes out of the wells when oil has been sitting in them. Worth doing while the cover is already off.
Check engine light diagnostics
When the misfire code arrives first and the leak is what turns up behind it.
Mobile oil changes
A leak that has been running a while shows up as a low dipstick long before it shows up as a puddle.
Mobile auto repair
The umbrella page, if you are working out whether your repair travels at all.
What people ask about this leak
If your question is not below, describing the smell over the phone gets you further than reading.
Is it safe to keep driving with a valve cover leak?
For a light seep, generally yes for a while, provided you watch the oil level and nothing is dripping onto the manifold in quantity. A heavier leak is different. Oil landing on an exhaust manifold that runs at several hundred degrees is a genuine fire risk on an older engine, and oil filling the plug wells is quietly destroying coils the whole time. Neither gets better on its own.
Why did my mechanic replace a coil and the misfire came back?
Because the new coil went back into the same well of oil. If the gasket is leaking into the wells, every coil on that bank is soaking, and they tend to fail one after another over a few months. Replacing coils without fixing the seal underneath them means buying the same part repeatedly. Cleaning the wells and sealing them is what stops the cycle.
Can this genuinely be done in my driveway?
On most engines, yes. The valve cover is the top of the engine, there is no jacking, no lift and nothing underneath the vehicle. The exception is a V6 or V8 where the rear bank hides under the intake manifold, which means a lot more comes off and the job runs much longer. We tell you which one yours is when you call rather than after we arrive.
Does the cover have to be replaced, or only the gasket?
Usually only the gasket. Two things change that. A metal cover warped by overtightened bolts will not seal against a new gasket and has to be replaced or resurfaced. A plastic cover with cracked bolt bosses, or one where the gasket is bonded in and not sold separately, means the cover is the part. We check with a straightedge before ordering anything.
My oil level keeps dropping but there is no puddle. Related?
It can be. Oil that leaks onto a hot manifold burns off instead of reaching the ground, so the driveway stays clean while the dipstick keeps falling. The same is true of oil pooling in plug wells, which has nowhere to run. A crust of baked oil down one side of the engine with no puddle underneath is a fairly reliable sign of this exact leak.
Should the PCV valve be looked at while you are in there?
Yes, and it is quick once the cover is off. A blocked PCV system raises pressure inside the engine, and that pressure pushes oil out through the weakest seal it can find, which is very often the valve cover gasket you just paid to replace. Checking it is a few minutes of work and it is the difference between fixing the leak and repeating it.
Describe the smell and the mileage.
Tell us the year, the engine and whether a misfire has shown up yet, and we can usually say on the phone whether this is a gasket alone or a gasket plus what the oil ruined. The mechanic doing the work is the one who answers.
HoursMonday to Sunday, 24 hours
Based inAmerican Canyon, CA
Nearby readingPlugs and coils · Job photos · Every service