Oil filler cap & oil pressure

[Halski]

My ZS went in for a service last Thursday. I checked the oil this morning and found that the oil filler cap just *wasn't there*.

Its bright yellow - and so very noticable.

There isn't much of a mess - hardly any at all and then only on the cladding above the filler point - and the oil level is right whrere it should be - I will be calling the stealership up later but I am sure they will humour me, thinking that I checked the oil later myself and forgot to put the cap back. I have driven about 400 miles without it and my question is will the absense of the cap have caused a drop in pressure likely to have caused any engine harm? the warning light never came on when it shouldn't and the temperature was always correct. I am very cross since I am meticulouis about oil checks and even do interim oil changes at 7,500 miles which is between the (overlong IMO) recommended change intervals....:mad:

TIA

Hal (who currently has the hump de luxe)

[BoinkCluster]

I doubt you'll have done any damage as, firstly, you've said that oil level is OK so you haven't been running with insufficient oil.

Secondly, a lot of engines have breather pipes next to the oil filler cap which are connected to the air intake - so these must actually be sucking air out of the engine - i.e. creating a slight vacuum which will lower pressure in the engine.

So, provided no 'foreign matter' got in to the hole where the filler cap should have been, you should be OK.

[7db]

I agree with BC -- provided no gritty bits have got in, the oil should be fine. You might do a quick interim change in the meantime if you want to be really sure. I wouldn't bother, unless you were driving particularly nasty roads.

As I understand it, having a closed system is not important for oil pressure - just the weight of oil -- the oil pressure decreases as the engine warms up and viscosity increases; doesn't increase with thermal expansion.

Do you have an oil pressure warning light? Did it come on?

[major9067]

I have to agree with what has been said so far. The only problem you might have is from contamination of the oil but this is so unlikely that you can pretty much dismiss the possibility.

The oil is not a closed pressurised system like the coolant. If you look under the radiator cap of you car you see a sping that helps maintain that pressure. As the engine heats and the water expands that spring maintains the optimum pressure by allowing water to bleed off to the header tank, when it cools, back it all comes again. There is no spring under the oil filler cap because that is all it is, a cap over the oil filler hole. Oil is circulated through the engine by a pump which sends oil through a variety of galleries to all parts of the engine. However, having got there it just basically drops back through a lot of holes to the sump at the bottom of the engine from where it gets sucked up by the oil pump and sent off again.

I hope I'm not over simplifying and treating you like an idiot I certainly don't mean to but I'm just trying to find an uncomplicated way of explaining why I don't think you need concern yourself. As they say here, "She'll be right mate" .

[Halski]

Thanks for the replies - informative, and exactly what I wanted to hear....

[noyourrights]

However, having got there it just basically drops back through a lot of holes to the sump at the bottom of the engine

:roflmao: :roflmao: :grinny:

your absaloutly spot on but ive never heard it described like that before:D

[7db]

Unless you are going round a corner, in which case it drops through a bunch of holes to the side of your engine. And whoops. Oil starvation. :)

[Hoon Devil]

Or in our old Rover, it just falls out of the engine through a bunch of holes in the oil cooler. Oops.

[noyourrights]

or as in my yzf1000 thunderace it gets past the rings because yamaha made the bores slightly oval:D

if you own a thunderace by shares in oil:D

but who cares on a bike that lifts the front wheel at 120mph and will go on to 170:D :D

on a private road of course:mb:

[MoneyMart]

If it had been a carburettor engine, you'd probably find it would have run very lumpy, or even not at all.

The reason is because the oil breather pipe (which is designed to avoid positivie crank-case pressure build up) is connected to the air intake and relies on a the engine back pressure restricting the amount of air it can suck into the carb. If you remove the oil cap, you let in unrestricted air which takes away the back pressure and over-leans the fuel mixture.

I don't *think* this applies to EFI engines though...

[Erica]

Perhaps when you revisit the dealership, you could demand one of those V8 ZT's as compensation, Hal. :D