Hi there

I have a corsa D 1.2
2012

I noticed after carrying out a service that if you remove the oil filler cap or the dipstick you get a strange whistling sound.

Any ideas what could be going on?

Thanks in advance


https://youtube.com/shorts/4onFV7Iiybo?feature=share

First thought would be +ve or -ve pressue in the engine.

When you remove the dipstick, if you put your fingertip over the top of the dipstick tube can you feel inward or outward pressure?

Not familiar with the engine, but does it have a crankcase ventilation system?

If so is it working correctly?

If it's not (jammed or blocked maybe) then there may be excess pressure building up in the engine.

You could drill a series of holes down the dipstick tube and play it like bagpipes.

I don't know how crankcases are vented on little diesels but I'd look at that as prime suspect. Whatever you're doing, you're changing the pressure bias across a small orifice connected to the crankcase somewhere by opening the filler cap and it's acting like a reed. You can hear the noise decay after you've plugged the hole as the pressure equalises again but it starts immediately when you open the cap so whatever's drawing is a substantially smaller orifice than the dipstick tube.

Removing the cap should produce some change in engine note/sound, however there is also a pcv valve in the rocker cover which has a diaphragm which can split and suck air from outside.
If you look at the rocker cover, opposite the filler cap there is a round housing with a small hole on the edge - check it is not sucking in air through this hole.

If it has failed, a genuine cover is about £100, there are copies on ebay in the £30-40 range, i don't know what sort of quality they are though.

Dave

I listened to the clip, the note is definitely E sharp, meaning the issue is in the upper (or lighter) part of the engine and not down by the crank. It's because the upper part has more air volume to create the resonance.

This seems to tally with obfrippers suggestion about the rocker cover.

Feel free to post more problem engine notes, I'll try to diagnose the issues using my "musical scale and air resonance within internal combustion engines theory". I wrote a paper on this subject many years ago.

I'm very pleased to make use of this little known theory from time to time.