Engine oil

Chevron Terry · Post by **Chevron Terry** » 16 Jul 2009, 11:38

Hi ,
Iam about to change the engine oil and filter on my zx diesel, which oil should I be buying .
The engine has done 112678 miles .
Terry .

Sid_the_Squid · Post by **Sid_the_Squid** » 16 Jul 2009, 11:52

This is a little subject I like to call "The Eternal Debate", a simple question but everyone has a different opinion on what the right answer is. I have spent many an enjoyable hour debating this subject with friends. There are of course a massive number of factors which can go into choosing the most appropriate oil, based on climate, season, driving style, engine type, mileage between services.

I'd say being in the UK, with a ZX diesel, assuming your driving sensibly with manufacture recommended service intervals. I would go for a semi-synthetic 10w-40 diesel oil from a well known brand. Make sure it’s a diesel oil, a lot of modern oils say on the back suitable for diesels, but you can get oils which are deliberately targeted at diesels which would be more appropriate.

I hope others will be comment on what their choices would be, especially if there offer dissenting opinions, it’s always good to hear as many sides to a storey as possible.

Post by **CitroJim** » 16 Jul 2009, 11:58

I would agree with your recommendation on oil Sid.

One thing to bear in mind using semi-synthetic is that for reasons of its own it occasionally fools the oil level warning light into believing the oil level is low after a hot start. This seems to affect diesels more than petrols for some reason...

Sid_the_Squid · Post by **Sid_the_Squid** » 16 Jul 2009, 12:32

Interesting bit of info about the low oil warning Jim, I get a low oil warning on my V6 from cold some days, don't understand why as there is 5.5 liters in there (the recommended amount in the handbook for a change) dipstick always shows just under max, only thing I can assume is a gremlin of sorts, have you seen such behavior before?

Sorry for the slight hi-jack Terry.

Post by **CitroJim** » 16 Jul 2009, 13:27

The one car I've never seen this behaviour on Sid is my V6, but then again it's not been on the road long enough in my care to show all it's little quirks yet

I'll have to look into the V6 a bit as I think it uses a different system to measure oil level, mainly because it does not have much of a sump pan!

My 2.1TD does it quite regularly and my Activa very occasionally.

Terry, sorry from me too for the hijack but it happens a lot on here and often these wanderings lead to some very interesting places...

Brigsygtt · Post by **Brigsygtt** » 16 Jul 2009, 13:47

I think the low oil level warning is a typical french gremlin.

My xantia low oil flashes on hot start at least 40% of the time & my old ax 1.5d used to do it at random. Neither used to use any oil & always on max on the stick...

As for oil, any half decent 10/40 derv oil should do aslong as you change it at service intervals.

citronut · Post by **citronut** » 16 Jul 2009, 19:26

i agree with Sid on the semi synthetic 10/40 but would sudgest a universal type, as i found the dedicated diesel oils cost a lot more

also just a medium quality is fine, especialy with the cost of engine oils has rocketed in the last year or so

regards malcolm

ianckt739 · Post by **ianckt739** » 17 Jul 2009, 00:58

The only thing I might add to the 'eternal debate' is regarding service intervals.

Having bought my little C3 with full Citroen history and seen the state of the oil I removed I'd be inclined so suggest that their service recommendations are a little on the optimistic side!

(Note that I am certainly not saying that this issue is specific to Citroen!)

Mine has a fairly long service interval recommended, something ridiculous like 12k, which I tend to cut in half for the oil changes.

On the subject of the oil level indicator I find that mine only ever reads accurately on the first start of the day when everything is at it's coldest. Maybe it's clogged up from all the long oil change intervals it had before now!

JamesQB · Post by **JamesQB** » 17 Jul 2009, 01:50

Anyone know how the oil level sensor detects oil level? Seen the flashing light even though oil at max before now and wondered if sensor becomes duff.

Sid_the_Squid · Post by **Sid_the_Squid** » 17 Jul 2009, 10:53

ianckt739 your right its not exclusive to Citroen, Advances in long life oils and anti freeze have made it possible for car makes to claim higher service intervals, based on the assumption that these premium products are used. This is an ever continueing trend which has existed for many years.
It has been proven that the modern synthetic oils, and Anti-freeze stand up better to higher mileages and higher ‘stress’ environments than their ancestors.
What happens if the recommendation premium expensive lubricants and fluids is ignored, its going to be pushing it a bit to expect the same service length from oil not designed to handle such strains?
Using inappropriate lubricants causes ‘black sludge’, this was a particularly prevalent problem in the early 80’s with modern designed engines subjecting old fashioned mineral oil to stresses and temperatures it was never designed to endure causing complete break down of the oil and ultimately the engine.

In short if you want to use the cheaper semi-synth option that’s fine just keep the services intervals frequent (3k miles ~ 6k miles) and your engine should be just as protected, stay in the recommended viscosity range, that’s important.
If you want a really long service interval you have to bite the bullet and spend £50~60 on fully synthetic engine oil.

Similarly if you drive in high stress environments (riding the red line or track days) I would not trust anything less than a fully synth, preferably the really expensive non-PAO synthetics.

I personally quite happy to spend £50~60 per oil change on PAO synthetics, but I still like to keep oil changes down to 10k miles max.

If you want to talk about really over optimistic service intervals; 'sealed for life' auto gearboxes.

dnsey · Post by **dnsey** » 17 Jul 2009, 11:05

Advances in long life oils and anti freeze have made it possible for car makes to claim higher service intervals, based on the assumption that these premium products are used.

Indeed, and this is nothing new. I used to have a set of service manuals for 1930s - 40s vehicles; many of those required regular and comprehensive servicing at 500 - 1000 miles, and in some cases a full overhaul including rebore was recommended at 10 000 miles!

Sid_the_Squid · Post by **Sid_the_Squid** » 17 Jul 2009, 11:14

Great stuff dnsey.
I'm always facinated to hear about these old fashioned regular service items, which now we would condiser a serious undertakeing. Its very interesting to me to think there was a time when takeing an engine head off for de-cokeing was a normal service procedure.

Post by **CitroJim** » 17 Jul 2009, 11:45

Sid_the_Squid wrote: there was a time when takeing an engine head off for de-cokeing was a normal service procedure.

Yes, and to make it easier, most valve heads had screwdriver slots in them to make grinding them in easier and the toolkit supplied with the car would often contain all the tols necessary to do all the major servicibng work.

Only last evening i read a long-term road test on a 1948 2CV. The engine was decoked at 32,000 miles and the garage was amazed at the lack of wear evident as it was normal then to need a rebore at such mileages. The garage did apparantly replace the exhaust valves during the decoke.

Nowadays, cylinder honing marks are often still to be seen in blocks having covered 150,000 miles. Just last weekend I saw an XUD9 block that had done over 100,000 miles with the honing marks still visible. Just goes to show how good modern oils are.

Sid_the_Squid · Post by **Sid_the_Squid** » 17 Jul 2009, 12:07

Just goes to show how good modern oils are.

Indeed, so much so* that I’ve heard the really good synth oils can actually stop engine wear, don’t know if it will actually stop it, but certainly it can drastically reduce it.

Which brings up a couple of interesting points with the modern car, my understanding is there is a bit of a debate weather manufactures should be shipping cars with fully synth oil from the factory, as the fully synth oils can actually arrest engine wear, which on a brand new engine would not allow for a ‘bedding in’ period.

Which is another point of debate, with ‘bedding in’ supposedly a thing of the past, apparently the manufacturing tolerances are so fine that bedding in is no longer required, well that’s the storey, hence why they ship with fully synth oil.

Prehapse there is no answer to these questions other than the results in the fullness of time. Still I certainly find them interesting topics.

*I apologise for that terrible Americanism.

Post by **CitroJim** » 17 Jul 2009, 13:09

They do say that fully synthetic oil should not be used until the engine is fully bedded-in because yes, it's so good that it stops the process.

Many expensive cars are shipped with fully synthetic in as the makers claim the engines are made to such precise tolerances that no formal running-in is required.

How true that is might be open to debate but conventional wisdom says to run-in on straight mineral oil and then say after 5,000 miles, swap to the fully synthetic stuff..

I'm still old-school and do an oil and filter change every 3.000 miles. Still the cheapest form of preventitive maintenance there is.