So I have been elbow deep in the engine compartment for a day now, refitting the intake manifold to fix a gas leak. I'm almost done (phew) and I notice that there are some serious oil-vapor deposits on the valve cover around the oil cap. Is the oil cap supposed to be a lump of hard plastic? I have been squinting at pics all day and can't figure out if there was supposed to be a gasket there that fell off or if that's all there is to it. Any advice?

MJ

 

If there's a missing gasket would that show up as a leak throwing off fuel trims?

I know mine has a certain sheen around the cap, but I chalk it up to additive drips from decades of oil fills.

 

I thought same thing Volkris said. This seal, along with the dip stick seal is air tight right?

John

 

oil fill cap has an O ring seal. It can harden and fracture.

 

I was under the hood today, so I glanced at my filler cap.

Between the threads and the underside of the cap I have an angled bit that looks like a sealing surface, but it's not obviously rubber. Pressing my fingernail against it, it feels kind of springy, but it might just be soft plastic. It was the same color as the rest of the cap, but it had seems that made it look like an independent piece, but my light prodding didn't make it move separately from the rest of the cap.

In short, I'd say if your cap is missing an angled surface, then it's missing a gasket. In slightly longer I'll rush to say I have a '97 so your '02 might be completely different anyway.

 

Oil cap, missing gasket?
Awsome help guys, thank you! So I've had a closer look and I have attached a photo of the underside of my cap. The black ring is just plastic and seems to be fused to the thread. To be honest I can't see a clear place where the gasket would sit. If there ever was a gasket it is clearly long gone. Can anybody share a photo of a cap with gasket intact?

 

 

Ya, I know what you mean... maybe it is just hardened beyond recognition..

 

it is supposed to be an o-ring. if it is hard and angled, it is due to age, heat and chemical exposure. you can either replace the cap or get a new o-ring.

the new cap that i purchased has a thick rounded o-ring on it. FYI the red oil cap is no longer available so keep it for the future. you can always replace the o-ring.

 

Nice picture! My filler cap is black, so I couldn't see by color that they were separate pieces. But yep, that's what my filler cap looks like, with the sealing surface after the threads.

 

It is definately an O ring. 5mm section, cannot remember the diameter.

 

So I guess it's new o-ring/new cap time! Thank you all for the help!

 

Just for fun, if you have a scanner handy, you might want to record your LT and ST fuel trims before and after replacing the cap.

 

@volkris -- great idea!