smart51
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| posted on 1/3/07 at 10:25 AM |
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hypothetical oil question
* this is not actually happening with my engine *
An engine holds 4 litres of oil. It loses 1 litre per month by whatever means. The owner tops up with 1 litre of oil per month. Working it out, 5
months after an oil change, 1/4 of the original oil remains. After 12 months just 1/30 of the oringinal oil remains. Given that an oild change
doesn't remove all of the old oil, should the owner do a complete oil change or just keep topping it up until the next oil filter change is
due?
Don't say he should fix the engine, it's not part of the hypothesis.
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02GF74
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| posted on 1/3/07 at 10:35 AM |
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it is like the african cooking pot where the pot is never emptied but food is just added to it so in theory there can be food that is many years old,
nice. 
I think your sums are wrong. (mine were wrong)
Assuming the new and oils mix totally then
after 1st top up, 75% is original oil
2nd top up 64 % is o.o.
3rd top up 56%
4 top up 42 %
5 top up 32 %
the question is how bad is the oil at the time of the top up?
[Edited to correct my math]
[Edited on 1/3/07 by 02GF74]
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DarrenW
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| posted on 1/3/07 at 10:37 AM |
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I would suggest the mileage covered should also be factored into the equation. If a kit car doing 5000 miles per year, id suggest keep topping it up
and replace completely with filter annually. If useage of car is performance related the driver may opt to change oil and filter totally more
frequently.
If heavy mileage say 20K per year id recommend a filter change every 6K or 10K as per service schedule and also full oil change.
Should maybe also understand how the oil is being lost - if leaking from sump and no excessive burning off then topping up should be OK (albeit
expensive for oil). If engine is burning the oil maybe other factors need to be considered ref other wear parts / consumables.
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scottc
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| posted on 1/3/07 at 10:42 AM |
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Month original New Rate of loss loss of original Loss of new
4 0 0.25 1 0
1 3 1 0.25 0.75 0.25
2 2.25 1.75 0.25 0.5625 0.4375
3 1.6875 2.3125 0.25 0.421875 0.578125
4 1.265625 2.734375 0.25 0.31640625 0.68359375
5 0.94921875 3.05078125 0.25 0.237304688 0.762695313
6 0.711914063 3.288085938 0.25 0.177978516 0.822021484
7 0.533935547 3.466064453 0.25 0.133483887 0.866516113
8 0.40045166 3.59954834 0.25 0.100112915 0.899887085
9 0.300338745 3.699661255 0.25 0.075084686 0.924915314
10 0.225254059 3.774745941 0.25 0.056313515 0.943686485
11 0.168940544 3.831059456 0.25 0.042235136 0.957764864
12 0.126705408 3.873294592 0.25 0.031676352 0.968323648
[Edited on 1/3/07 by scottc]
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fesycresy
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| posted on 1/3/07 at 10:46 AM |
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It's your wifes car isn't it ?
quote:
* this is not actually happening with my engine *
[Edited on 1/3/07 by fesycresy]
-----------------------------------------------------------------------------------------------------
The sooner you fall behind, the more time you'll have to catch up.
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scottc
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| posted on 1/3/07 at 10:46 AM |
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hmmm my thinking is yes do an oil change.
Think of all the small particles drained out the sump with the oil. depending on the leak they're going to remain in the engine if you
don't change the oil.
Edit to make no into yes, cos I'm an idiot
[Edited on 1/3/07 by scottc]
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Tiger Super Six
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| posted on 1/3/07 at 10:58 AM |
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Out of interested this does actually happen with my car. I have to regularly top it up with a lot of oil.
My question is:
I don't have an oil leak,
The emmissions at MOT were nearly pure
There is no oil up the back of the car
Where is it going???
Mark.
PS - Should have said this is on Tin Top.
[Edited on 1/3/07 by Tiger Super Six]
Mark
Tiger Avon
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smart51
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| posted on 1/3/07 at 10:58 AM |
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quote:
Originally posted by scottc
hmmm my thinking is yes do an oil change.
Think of all the small particles drained out the sump with the oil. depending on the leak they're going to remain in the engine if you
don't change the oil.
wouldn't those small particles be filtered out by the oil filter?
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scottc
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| posted on 1/3/07 at 11:08 AM |
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quote:
Originally posted by smart51
wouldn't those small particles be filtered out by the oil filter?
good point. I suppose it depends how small they are.
which is why those stick on magnet things for oil filters seem to work.
ok. I'll revise my answer to don't bother with the oil change and stick some magnets on the filter. lol.
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DarrenW
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| posted on 1/3/07 at 11:08 AM |
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To a point they will be filtered out but i guess some may remain in the sump. Whatever happens regular filter change is recommended.
Ref particles remaining in sump - even with full oil change its hard to get these out. Im happy with my ZR that i was able to clean sump right out
when i swapped engine over so in theory with reg maintenance it should stay relatively clean.
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02GF74
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| posted on 1/3/07 at 12:18 PM |
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quote:
Originally posted by Tiger Super Six
Out of interested this does actually happen with my car. I have to regularly top it up with a lot of oil.
My question is:
I don't have an oil leak,
The emmissions at MOT were nearly pure
There is no oil up the back of the car
Where is it going???
Mark.
PS - Should have said this is on Tin Top.
[Edited on 1/3/07 by Tiger Super Six]
there are only two places - either via the combustion chambers (burnt) or out of the block leak.
what do the plugs look like? is eaxhaust smoeky? seems from what you say it is not going that way.
so leaks - you see no drips when stationary nor on the block so can it leave the engine only when driven (but leave no trace on the block??)
it is a mystery for sure.
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MikeRJ
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| posted on 1/3/07 at 12:27 PM |
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Some modern cars (notably Alfas!) tend to burn what would be considered by many (by me at least!) to be an unacceptable amount of oil; a litre per
thousand miles or more is not uncommon but they don't appear to be visibly smoky using this much oil.
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smart51
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| posted on 1/3/07 at 12:36 PM |
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quote:
Originally posted by Tiger Super Six
Out of interested this does actually happen with my car. I have to regularly top it up with a lot of oil.
My question is:
I don't have an oil leak,
The emmissions at MOT were nearly pure
There is no oil up the back of the car
Where is it going???
My old R1 engine used to go though a lot of oil. It never dripped on the garage floor. Eventually I found that the timing hole bolt was missing.
Whenever the car had the brakes applied hard, the oil would surge up and spurt out of the hole.
It sill burned a bit of oil but only when it was given a damn good thrashing. At MOT revs it burned cleanly and sweetly.
[Edited on 1-3-2007 by smart51]
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britishtrident
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| posted on 1/3/07 at 01:12 PM |
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Isn't worth changing the oil the engine is clearly on its way out anyway.
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trogdor
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| posted on 1/3/07 at 01:21 PM |
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it does depend on how use the engine i think, our micra doesn't use oil until its being thrashed on the motorway home, is only a four gear car
so its reving alot and in the 400 miles there and back it uses about 2 pints!
it doesn't use it much at any other time tho, just a reasonable amount
if you are topping up the car reguarly then you are going to be adding new oil all the time, so an oil change is not as critical though their will
always be a bit of old oil in there, thoug the filter will deffo need changing at some point as it gets clogged and loses effectiveness.
[Edited on 1/3/07 by trogdor]
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Ketchup
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| posted on 1/3/07 at 01:32 PM |
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they arnt vauxhalls with ecotecs in are they? 
I only say this because i have had lots of problems with oil consumption on these. I have worked on vauxhalls still under warranty with this problem,
and vauxhalls official line is that 1ltr oil loss over 1000 miles is acceptable, and will not entertain a warranty repair unless it consumes more than
that, how they can see it that way i dont understand as they have 10000+ service intervals on most of the petrol models!
I am not saying every vauxhall has this problem, and it certantly is not just them, as we sell and maintain all makes here, but vauxhalls do seem to
be the worst culprits for it.
I would personally use a good engine flush, and then change oil and filter every 5-6k miles
jus my 2 cents
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britishtrident
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| posted on 1/3/07 at 02:35 PM |
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"Invisiable" (ie smokeless) oil consumption tends to be crank presurisation problem, which can be either due to crankcase breather
problems or compression rings that aren't sealing.
Excessive oil consumption with grey smoke immediately after idling, tends to a valve guide or stem seal problem.
Where the oil consumption is accompanied by excessive smoke on on flooring the throttle under load tends to be an oil control ring problem.
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Tiger Super Six
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| posted on 1/3/07 at 04:11 PM |
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Yes it is a Vauxhall (Astra).
There are no leaks that can be seen (even got under it at the MOT to be sure) and when I mentioned it the guy at the MOT was surprised as the gases
were so clean.
Fortunately (touch wood) it is not a problem, only that I have to buy oil more than on any other car I have owned.
What actually is the cause? there must be a problem if Vauxhall do fix it if it uses more than 1ltr?
Thanks for the comments.
Mark.
Mark
Tiger Avon
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jollygreengiant
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| posted on 1/3/07 at 04:27 PM |
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Peugeot 406td came on the taxi fleet with 90k on the clock.
Changed the cambelt (repeatedly).
Changed the fuel filter once (started loosing top end revs and the ecu light flicked on occasionally, but ok after change).
Kept passing mot test & 3 hackney test a year.
Engine would smoke heavily on initial acceleration to full throttle after 2 - 3 days of running around town (turbo oil seals going).
Changed gearbox and clutch when gearbox bearings started chirping at 246k.
Vehicle finnaly taken off fleet today 265k.
In all that time we never once changed the oil filter and just kept topping the oil up.
It still starts ok and pulls cleanly to 90+mph.
[Edited on 1/3/07 by jollygreengiant]
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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martyn_16v
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| posted on 2/3/07 at 07:14 PM |
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quote:
Originally posted by MikeRJ
Some modern cars (notably Alfas!) tend to burn what would be considered by many (by me at least!) to be an unacceptable amount of oil; a litre per
thousand miles or more is not uncommon but they don't appear to be visibly smoky using this much oil.
I was going to ask if was an Alfa SWMBO's one does about a litre every 500 miles or so, excessive even for an Alfa  I just know it's
going to be something expensive and I really can't be bothered with dealing with it right now
Which reminds me, I was supposed to stop at the factors and pick up some brake pads for it today too 
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jollygreengiant
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| posted on 2/3/07 at 10:11 PM |
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Ford reckon that 300miles per pint is not excessive.
However if it is an Alfa I would not worry too much. Just make sure that you DO keep it with enough oil in it. Alfa change an AWFUL lot of engines
because they have run low because the reps/company drivers DON'T check the oil levels.
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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