Why 12 month oil change on low use vehicle?

You've changed the subject again. Mayo forms in the top half of the engine, not in the crankcase. Cold damp air in large quantities is found in the top half of the engine, not the bottom half. This is not coincidence, there's a link. I say again that there is not sufficient air ingress to the bottom half of any modern engine to cause this-

"Every night when temperatures drop condensation forms on the block walls. It forms dropplets that run off and drain into the oil. If not changed a steel sump will rot from the inside and fall off."

Which is what Peter Hill posted earlier. Do you agree or disagree with that claim?

Steve

"shazzbat" gurgled happily, sounding much like they were saying:

Or the... what?

"shazzbat" gurgled happily, sounding much like they were saying:

There's also a link between the two. A nice big open link, so oil can drain back from the head to the crankcase. It's why you see the mayo when you open the OIL FILLER CAP to pour oil in - and how that oil then FLOWS TO THE SUMP.

Sorry, I thought we were discussing the issue of condensation in the crankcase running down and rotting the sump off. The conditions in the top and bottom half of an engine are very different, despite being linked. Allowing oil to fall to the bottom is very different from allowing atmospheric air into the engine, along with it's attendant moisture. [1] Incidentally, do you agree or disagree with Peter's statement -

"Every night when temperatures drop condensation forms on the block walls. It forms dropplets that run off and drain into the oil. If not changed a steel sump will rot from the inside and fall off."

Steve

Have you never seen an inlet manifold, with pipes attached to various places, like engine breather, brake servo, advance/retard etc? And yes I know the latter applies more to somewhat older engines with carbs, not to mention cb points in a distributor. But my point remains that the interior of the engine is not open to atmosphere, except by various means which have serious obstructions, which in turn means that the statement by Peter Hill -

"Every night when temperatures drop condensation forms on the block walls. It forms dropplets that run off and drain into the oil. If not changed a steel sump will rot from the inside and fall off."

is incorrect. Do you agree or disagree with his statement?

Steve

"shazzbat" gurgled happily, sounding much like they were saying:

That's odd. I thought we were discussing oil change intervals on low mileage vehicles.

In what way? What miraculous effect prevents air from flowing freely up and down those relatively great big chambers linking head and crankcase?

And, obviously, apart from the crankcase breather being connected to the airbox. And any inlet or exhaust valves that might be open whilst the engine's not rotating. And any condensation that may form due to temperature changes.

I've not commented on it, because I have no opinion on it.

I've never seen a sump rot from the inside out. I've seen them rot from the outside in, though. I don't find it impossible, but it's more likely to occur due to the oil becoming acidic and corrosive from combustion byproducts.

"shazzbat" gurgled happily, sounding much like they were saying:

Strangely, yes. Quite frequently.

I've also seen the inside of airboxes. Have you? Can you guess why they're called "air intakes"?

Maybe more of a problem because there never was any corrosion protection internally, maybe why jerrycans are lined.

The engines are not outside, but in a shed so still exposed to quite drastic temperature variations.. The breathers are usually only taped over with a bit of insulation tape or have a cork rammed in them. Some are effectively brand new after rebuilds, some are straight removals from running cars that have had nothing done to them other than a drain down of fluids and a steam clean followed by a quick wipe over with Shell Ensis long ago, some might have had a quick blast of WD40 down the breathers, and all will have had a quantity of clean engine oil down the bores . The worst damage I've seen from one that has been there since the early 80's was a bit of pitting on the bearing shells presumably from residual acid in the oil. There was no evidence of water at all in the sump.

Why do you think that? And how's it get into the dipstick tube?

They're connected together, that is indeed a link, both rigidly & via some holes. It doesn't matter whether the condensation occurs in the top, the bottom or both, it'll get mixed round the engine once you start it.

Fine, you can say it all you like, but if you get the oil analysed there'll be water in it.

I'd say it was a slight exaggeration, wheras the suggestion that mayo only forms in the top is complete bollocks.

"shazzbat" wrote

Whether or not the process of corrosion occurs, the idea that corrosion could thin the material down round the entire sump circumference so evenly that it could suddenly unzip itself has to be fantasy...

The first pinhole would surely cure the problem.

Well thread drift always happens. But I came in to this thread in response to the question from David Hearn about what happens when the engine isn't running, specifically the lack of air ingress.

Crankcase pressure.

Yes, I said someone would point to the air intake, check out my first post in this thread.

Steve

Weren't you just coughing and spluttering about air intakes? My point stands, that the air intake is not open to atmosphere to any great extent when the engine is not running, see my first post in this thread.

Steve

I thnk that, or rather know that, because whenever I've stripped down an engine I've found mayo in the breather pipes, cam boxes filler caps, and yes, dipstick tubes, but not in the crankcase. And it doesn't 'get into' the dipstick tube, it forms in there.

But not in sufficient quantity to cause the sump rotting off, which is the claim I was responding to

And you're the one who was saying that short journeys snap cambelts, right?

Steve

I've found a film of it on the sump.

Yep, if you do lots of short journeys your cambelt will die at a far lower mileage than if you drive it down the motorway, or any reasonable distance. As is advised in every service schedule .

"shazzbat" gurgled happily, sounding much like they were saying:

Even when the engine's not running?

"shazzbat" gurgled happily, sounding much like they were saying:

So you've never seen one. Thank you for confirming that.

Dunno. My diesel Alfa is supposed to work out for itself when an oil change is due; it doesn't get changed at the regular service intervals. After nearly 3 years and 25,000 miles it's still got the original oil in it.

-- DAS

WTF?

Did you see my first post in this thread? Try not to be bizarre.

Steve

Yes. As is advised in every service schedule by the people who want to do the job and sell you the parts. This is not engineering, it's marketing. A moment's thought would have made you realise that it's bollocks. They know that light usage will make a cambelt last a long long time, so they try to scare the gullible into having it done when they don't need it. A bit like the claim about the increased need for oil changes. Who tells us that? Oh yes, the oil companies. Fancy that.

Steve