Oil leak through filler cap

[ZCube]

Hi

When i went to fill my screenwash the other day on my Nissan Cube I noticed it looks like oil is getting out of the filler cap. So a couple of noddy questions - could it just be the seal on the filler cap? the o-rings on it look fine and don't look perished and probably the second more important question is should oil be getting anywhere near there in the first place? Happy enough to try a new filler cap or o-ring but want to make sure i'm not ignoring a more important problem!

Ignore the white hairs on the filler cap i think next door's cat has been sleeping in my engine bay! sadly the marks are too dark to dismiss as cat wee! ;-)

[Decky_Q]

I would normally dismiss that as a bit spilled when filling the oil. To be sure get a rag with some fuel on it and clean it all, if it appears again then look further.

[paintman]

^^^ As above.
Doesn't look excessive.
The seals will harden over time & might be worth considering a replacement if it worries you.

Oil mist will get everywhere inside the engine & you may also get oil thrown up by the cam and/or valve train (OHC or OHV) & I would expect to see oil on the inside of the filler cap

Might be an idea to check the crankcase breather isn't blocked/partially blocked. This relieves crankcase pressure & usually there's a fair bit of oil vapour. Normally routed back into the engine through the air intake side & the vapour will be burnt during combustion.

If they get totally blocked the crankcase will overpressurise & you may well find oil leaks from seals & gaskets.
Had that on my RRC 3.5V8 when I bought it - the breather was blocked solid & oil leaked out of all sorts of interesting places!

I'm not sure of the breather setup on your particular engine so you'll need to do a bit of research.

Edited by paintman on Tuesday 27th September 10:35

[ZCube]

Thanks for your replies guys. I've purchased a new oil filler cap from nissan - it was cheaper than most after market ones and i know it'll fit - and have cleaned off some of the old oil so we'll wait and see. So far it's looking ok, i have a longish journey this weekend so will see how it looks after that

[ReverendCounter]

From what I understand, an increase in crankcase pressure can be caused by worn piston rings - are you using more oil than you think you should? If the new oil filler cap doesn't solve the issue, could be that.