* 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.

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]

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.

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]

It's your wifes car isn't it ?

quote:

---

* this is not actually happening with my engine *

---

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]

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]

quote:

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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.

---

quote:

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Originally posted by smart51
wouldn't those small particles be filtered out by the oil filter?

---

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.

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]

---

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.

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???

---

Isn't worth changing the oil the engine is clearly on its way out anyway.

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]

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

"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.

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.

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]

quote:

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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.

---

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.