Why such frequent oil changes?

BX Tech talk
AlanS
BXpert
BXpert
Posts: 841
Joined: Mon May 16, 2005 9:53 pm
Location: Queensland, Australia

Post by AlanS » Sun Feb 05, 2006 11:16 am

Stewart (oily!) wrote:My old motor vehicle lecturer would say if the oil is staying clean it could be because it might not be picking stuff up :twisted:
Stewart
I've heard this one too, but excuse me if I'm wrong, but isn't oil supposedly there to "lubricate" not act as a cleaning agent? Dirty oil is full of contaminents and they get circulated in the system and wear things out as usually, they're either abrasive or sorrosive.
Methinks that's an old wives tale.


Alan S
By the time you're old enough to know it all, you can't remember why you were learning.

Gareth Wales
BXpert
BXpert
Posts: 267
Joined: Wed Jun 01, 2005 7:12 pm
Location: Snowdonia

Post by Gareth Wales » Tue Feb 07, 2006 8:01 pm

[quote="DavidRutherford"] but I don't use flushing oil, as it's a) expensive and b) bad for the engine if any remains in there. So instead, I run 2 litres of normal engine oil round at no more than idle for 5 minutes. It's just enough oil to make sure the pickup is always submerged, and there's always oil pressure, but not enough to actually drive on (it would overheat in no time at all)

David - are you saying you drain off the old oil and run the engine (at idle) with just two litres?

User avatar
DavidRutherford
BX Digit man!
Posts: 2704
Joined: Wed May 18, 2005 5:07 pm
Location: Placing comments on YouTube.

Post by DavidRutherford » Tue Feb 07, 2006 8:10 pm

Yes.

In an XUD, 2 litres is enough to make sure the oil pump pick up is always under the oil level, and there is always oil pressure.

But, that's only true when the vehicle is stationary.

It's not enough oil to drive on though, as it (the oil) would overheat in no time at all, and in the slightest corner you would loose oil pressure.

when the engine is idling, the demands on it's oil are very small when compared to high load/speed, so it doesn't do any harm running on just 2 litres of oil.

What it does do is clear out a load more of the black oil that you can't drain from the galleries, and means that you haven't left thin flushing oil in there, ready to contaminate the new oil.

Works very well, and for 2 litres of oil, is worth it. I have done the same on just one litre of oil in the past, but had a slightly flickering oil pressure light. Probably not a problem, but I prefer not to see flickering warning lamps, and at £1 a litre for oil, it's not worth worrying about.
this might be a signature

User avatar
Way2go
Over 2k
Posts: 7279
Joined: Fri Jan 13, 2006 3:15 pm
Location: RCoBerkshire
x 2

Post by Way2go » Tue Feb 07, 2006 9:10 pm

AlanS wrote:
Stewart (oily!) wrote:My old motor vehicle lecturer would say if the oil is staying clean it could be because it might not be picking stuff up :twisted:
Stewart
I've heard this one too, but excuse me if I'm wrong, but isn't oil supposedly there to "lubricate" not act as a cleaning agent? Dirty oil is full of contaminents and they get circulated in the system and wear things out as usually, they're either abrasive or sorrosive.
Methinks that's an old wives tale.


Alan S
I understood from the claims by Castrol etc of years ago that one of the differences between "good" oil & cheap oil was in the quality of the detergents used in it without degrading it's lubrication qualities. Consequently it should clean & also hold the muck in suspension.

AlanS
BXpert
BXpert
Posts: 841
Joined: Mon May 16, 2005 9:53 pm
Location: Queensland, Australia

Post by AlanS » Tue Feb 07, 2006 9:37 pm

Way2go wrote: Consequently it should clean & also hold the muck in suspension.
Suspended where when it's being circulated under pressure through the system?

Oils have detergents and dispersants in them usually which are in there to wash off any build ups and break them up to reduce the amount of clogging up of oilways, but remember Castrol is also the one who claims to make an oil that is "magnetically attracted" to metals (everybody else refers to that as 'semi-synthetic oil' ), but how do they hold metal particles? Refer to any CX owner which had a magnetic sump plug that always came out with a marble sized blob of metal particles attached, or to anyone who has ever had an underserviced 16V engine apart and has had to drill out the ends of the oil gallies so that the build up of garbage can be pushed out using metal rod as it's too solid for industrial degreasers to remove. Old oil also is acidic and again helps creeate premature wear due to this.
Oil is the cheapest thing you use on the car yet one of the most important, so I can never see the logic in trying to drag out changing it.


Alan S
By the time you're old enough to know it all, you can't remember why you were learning.

User avatar
Way2go
Over 2k
Posts: 7279
Joined: Fri Jan 13, 2006 3:15 pm
Location: RCoBerkshire
x 2

Post by Way2go » Thu Feb 09, 2006 3:50 pm

AlanS wrote:
Way2go wrote: Consequently it should clean & also hold the muck in suspension.
Suspended where when it's being circulated under pressure through the system?

Alan S
Suspended within the oil until it is substantially removed in transit through the oil filter.

I was agreeing with Stewart about the jobs the oil was doing. I think also that the less time an oil spends in an engine there will be less obvious contamination/colouration per change but does changing more frequently than manufacturers recommended give great advantages; the chore of oil changing is probably more significant to most than the cost.

I usually change my oil at a maximum of 6000 miles on the petrol engine and am not an advocate of extending the period but am aware that a lot of the newer cars today have recommended change periods of 10,000 or 12,000 miles. I am unaware of whether this is because of mechanical improvements/quality of the car or in the evolutionary improvements in the formulation of the oils of today.

The point on the metal filings is interesting but surely if these enter the pick-up they are even more surely going to be trapped by the filter than the other contaminents?

Stewart (oily!)
1K Away
1K Away
Posts: 1604
Joined: Wed May 18, 2005 6:23 pm
Location: North Wales

Post by Stewart (oily!) » Thu Feb 09, 2006 4:48 pm

I have a big magnet stuck onto my oil filter, hopefully grabbing metallic bits as they come past and allowing them to go with the filter when its changed, many years ago my company investigated a device called a bypass oil filter, this was a filter body holding what looked like a toilet roll, fed from the oil pressure switch hole (switch remounted on a tee piece) and returning to a hole bored in the rocker cover once fitted the makers claimed the oil could remain in for 60,000 miles and the original filter need never be changed, we fitted it to a Cortina which was a high miler and the oil always looked like it had just been changed, one pitfall was apparently that the filter was so fine it removed essential bits of the oil too, the lovely castrol long chain molecules were too big to pass!
Stewart
TZD 19 TD one of the few
Xantia Td estate, going soft

st gilles

Post by st gilles » Thu Feb 09, 2006 10:38 pm

In France, maybe here as well you can buy a replacement drain plug with a magnet attached........idea is that it picks up the 'swarf' in your engine and it can be wiped off when you change the oil. Great idea I thought, until I really thought about it. Lets face it if you've got that sort of metal floating about in the engine there must be something big going wrong in there. I s'pose it would be a good primary indication of things going wrong but I think I'd rather not know!

AlanS
BXpert
BXpert
Posts: 841
Joined: Mon May 16, 2005 9:53 pm
Location: Queensland, Australia

Post by AlanS » Fri Feb 10, 2006 12:24 am

Here's a bit on magnetised wrap arounds for oil filters;

http://www.oneeyeindustries.com/domestic.asp

and if you've got an hour or so to spare, a write up on various aspects of oils and associated myths and facts.

http://www.carbibles.com/engineoil_bible.html



Cheers,


Alan S
By the time you're old enough to know it all, you can't remember why you were learning.

User avatar
Mike E (uk)
1K Away
1K Away
Posts: 1115
Joined: Sun Aug 14, 2005 9:10 am
Location: High Wycombe, Bucks

Post by Mike E (uk) » Fri Feb 10, 2006 9:10 am

My 1971 mini had a sump plug magnet, and when I changed the oil it was covered in a heap of metal filings

As the gearbox shared its oil with the engine, perhaps these bits were from the worn synchromesh, but considering how much metal came out, the car ran fine.

Anyone any ideas where it was coming from?

Mike

AlanS
BXpert
BXpert
Posts: 841
Joined: Mon May 16, 2005 9:53 pm
Location: Queensland, Australia

Post by AlanS » Fri Feb 10, 2006 9:21 am

Anyone who owned a CX (I owned a few) will tell you how there was a dag of metal on the magnetic sump plug at every change so at least some of it came from within the engine. :shock: :shock:


Alan S
By the time you're old enough to know it all, you can't remember why you were learning.

User avatar
DavidRutherford
BX Digit man!
Posts: 2704
Joined: Wed May 18, 2005 5:07 pm
Location: Placing comments on YouTube.

Post by DavidRutherford » Fri Feb 10, 2006 10:47 am

Most of it is very tiny machinings from the piston rings, bores, and oil pump. To be honest, a magnet in the oil to pick them up is of no real benefit other than allowing you to see them. If they're not caught on a magnet then they end up in the oil filter.

that said, if you had a magnetic sump plug in a 1980's and early 1990's Vauxhaul OHC engine, it was a good indication that your camshaft was/wasn't breaking up!

tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic tic

(anyone who's had one of these engines at high mileage with crap oil will know what I'm on about!)
this might be a signature

Geoffrey Gould
BXpert
BXpert
Posts: 545
Joined: Sat Jun 25, 2005 7:26 pm
Location: Bristol.UK.

Camshaft wear.

Post by Geoffrey Gould » Fri Feb 10, 2006 1:11 pm

Shades of Ford pinto cams/followers and spray bars, didnt tic tic more like knock knock could be heard for bl++dy miles when the next doors Ford would arrive in the early hours of the morning. Ah memories.
Cheers.
Geoff.

adamskibx
BXpert
BXpert
Posts: 950
Joined: Fri Jul 22, 2005 9:26 pm

Post by adamskibx » Fri Feb 10, 2006 6:01 pm

Very interesting thread. I have just changed the oil on the Merc 190 as I have done 3000 miles since owning the car and dont know when it was done before that. Its odd as the oil seemed cleaner than any other cars oil ive ever owned, yet the oil pressure has dropped in the time ive owned the car. It would always be at 3 on the guage apart from when hot and in traffic when it would drop to 2, but this has dropped to 2 even when cold and the engine needs 2000 RPM to keep it at 3 when it used to be at 3 at 1000 RPM. Could it be that a thicker oil was used when I first had the car, or rather that something is wearing out?

User avatar
DLM
Our Trim Guru
Posts: 1569
Joined: Mon May 16, 2005 6:41 pm
Location: Gosport, Hampshire, UK
My Cars: None since the last BX.
x 1

Post by DLM » Fri Feb 10, 2006 6:16 pm

A couple of questions. What oil is recommended for the car, and is that what you put in? If the car was scrubbed-up before sale then somebody MIGHT have put in thicker oil than recommended to keep that gauge looking healthy...

On the other hand, depending on the mileage, a very slightly thicker oil might be a good idea when it gets fairly high. Cars (or rather their engines) seem to like being fed consistently with the same grade of oil, and a change to something too thin or slippy can cause a lump to become smoky in next to no time.
Relying on two wheels and musclepower since the last BX (or any car) had to go.