Tom,
This has been discussed several times before in the Backroom. The usual recommendation is to point your browser at Chris Longhurst\'s Oil Bible site where you\'ll find a rundown on what makes up a synthetic lubricant:
www.chris-longhurst.com/carbibles/index.html?menu....l
Regards
Rich
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Cheers a very useful site but not exactly what I'm getting at, do I need synthetic or semi synthetic in this engine?
I have a recollection of HJ saying this was a candidate for fully synthetic oil???
Someone please tell me before I put the wrong stuff in!
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Tom,
If you look in the handbook I think any 10/40 SG rated oil is suitable.
If it were my own car I would use Vauxhall semi-syn, a good oil often at a good price.
David W
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Tom
Most BMW dealers seem to use fully synthetic these days, but there are concerns about using this in high mileage cars in that it may dislodge deposits.
I'd suggest a decent 10-40 semi-synthetic for your car, which, judging by my (albeit newer) handbook will meet BMW's requirements.
Regards
John S
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With all due respect for JS, I'd use fully synthetic. Dislodged sludge SHOULD be trapped in the filter, though I accept that it's theoretically possible that some muck could get stuck somewhere else.
Has anyone heard of any actual example of dislodged sludge causing a problem?
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I haven't had any problems myself with dislodged sludge but I believe that problems of this kind were experienced 'in the old days' when going from a low-detergent to a high-detergent oil.
Any dislodged sludge will meet the oil pump inlet strainer before it gets to the filter and it could block either of them with dire results. Unlikely but possible if there's enough of it. I would use flushing oil before introducing a significantly different lubricating oil 'just in case'.
I use fully synthetic in my own BMW 2.5 engine but I would have thought that semi-synthetic would be perfectly OK if changed at the proper intervals (and here I would rely on the BMW service indicator).
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Dizzy
Yes, I too use sythetic in my car. However, the newer BM's seem to put in a lot of miles between changes - mine gives 2k between green lights, and I don't like running for 10k between changes. So, I change oil every intermediate 5k miles, not resetting the service indicator.
Provided the engine's not too dirty, I think a shift to synthetic should be OK. As you say use a flushing oil, or alternatively change the oil and leave it in for a thousand miles to clean up the engine and then shift to the synthetic.
Regards
John S
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John,
My BMW, obviously a bit older than yours, goes about 7000 miles before the service indicator calls for an oil change. Unlike yourself, I would be quite happy to go 10000 miles with synthetic oil, especially since a BMW-owning friend was advised by Mobil that he could safely omit every other oil change if using synthetic oil.
Incidentally, I believe that my 1992 model calculates the servicing intervals from a variety of data (type of driving, number of cold starts, etc. etc.) whereas the newer ones calculate purely from the fuel usage. When you think about it, the result should be roughly the same! Either way, these engines are so long-lived that I have complete confidence in the service indicators.
I experienced a strange situation regarding the oil in my Triumph 2500 during restoration after it had stood abandoned to the elements for 10 years. On removing the sump, I found that the oil had turned into one huge lump of jelly, definitely too viscous to go through the strainer and filter! This reminded me of a situation at work many years ago when our engine machinists complained of bad smells from the coolant they were using. The coolant supplier, Edgar Vaughan, found that this was caused by bacterial action and cured it by adding an anti-bacteria chemical.
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Afew years ago the son in law bought his Vauxhall Carlton up to my place for an oil change.
It was nice and warm and drained down well into my usual draining can.
Next day when I took it down to the local disposal tank it would't drain out.
"When was the last time you changed the oil" I asked. "Don't think I have says he"
The puzzle is how did the starter motor manage to turn the engine over with a sump full of jelly when cold. And the engine had over a 100k on it before he sold it.
alvin
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I once bought, for very little money, an Audi 80 which had a broken bonnet release cable. When I finally prised the bonnet open, I found the oil was jet black and there wasn't much of it, also the area inside the filler cap looked a bit gungy. Anyway, I filled it up with nice fresh high quality oil, fitted an oil filter and off I went. Thirty miles later, at 70 mph on the M11, it put a conrod through the side of the block.
The post-mortem revealed that the strainer on the oil pickup pipe in the sump was totally clogged with black gunge, resulting in loss of oil pressure. The sun was shining on the instrument panel, so I didn't notice the oil pressure light come on.
Now, when I buy a cheap old car with a suspect history, I use the cheapest oil I can find. Good quality oil has detergents in it - in this case, I suspect that they quickly stripped the black gunge from the inside of the engine, and it fell into the sump in large lumps. I could be wrong with that theory, but it was the third time I had an engine suffer a bearing failure shortly after an oil change, and up to that point I had always used the best oil I could afford. My Polo, despite a heavily gunged engine, is running very sweetly on supermarket 20/50 at £2.99 a gallon, and still has plenty of oil pressure.
Richard Hall
bangernomics.tripod.com
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Dizzy
There's no doubt that BMW have increased the mileage/service between oil changes. My previous 1990 car, like yours, would cover 7500 between service intervals, whilst my present '99 car covers 10000. The very latest cars seem to have pushed this to about 15000 miles. Both instruction books for my cars have stated that the system considers miles, cold starts, revs etc in calculating optimum service intervals. I get the impression that the system our cars use has a max mileage at which each light goes out, which can be reduced by exceeding a preset number of cold starts, idling time etc. I did read that the latest system uses total fuel burn as a much simpler analogue of the appropriate service interval, which is a very neat bit of lateral thinking.
I may be over cautious by changing oil at the halfway point, but the instruction book does recommend an annual change if the annual mileage is under 5000, and my car is currently doing little more than that.
What is more interesting is that the instruction book indicates that even relatively basic A2/B2 oil is apparently acceptable in the engine, despite the service interval, whereas the dealers use a top end synthetic.
As for your Triumph, I imagine the outdoor location allowed some sort of either oxidation or bacterial effect on the oil - I wondered about this when my Minor was off the road for 10 years in the garage, but the oil was still liquid. I didn't worry, as I'd rebuilt a spare engine for use anyway.
Regards
John S
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"..advised by Mobil that he could safely omit every other oil change if using synthetic oil"
That sounds like terrible advice! Oil does a lot more than lubricate - it cools, transports debris, dissolves combustion products, neutralises acids and so on, most of which are independent of the oil base material. Extending service intervals damages engines far more than choosing the wrong brand of oil, IMHO.
Manufacturers compete with one another to stretch the interval to create the impression that their cars require less maintenance, safe in the knowledge that the original purchaser is unlikely to keep the car long enough to reap the consequences...
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JBJ:
1. Surely the chemical make-up of the oil will have little influence on its ability to cool and to transport debris to the filter, unless of course the oil has become largely replaced by contaminants in which case we are already in trouble!
2. I would have said that the ability of oil to dissolve combustion products is unchanged until it reaches close to saturation. However, 2% carbon contamination has been found by Perkins to be the maximum limit that should be tolerated in a diesel engine and I suspect that this would also apply to spark-ignition engines.
3. Unlike mineral oils, synthetics have little reaction to the products of combustion and they readily part with these products on passing through the filter.
4. Mineral oils need a cocktail of viscosity index improvers (polymers) to give them their rated viscosities and thus the required flow rates and resistance to film shear at varying temperatures and loads. The polymers soon start to break down and lose their effectiveness, as well as being prone to burning and thus contaminating the base oil with their own products of combustion! Synthetics have very little polymer content; some have none at all.
5. Some oil manufacturers say that the engine manufacturers' specified oil change intervals can be increased *three-fold* with synthetics for engines in normal service. Let's ignore the engine manufacturers' recommended service intervals, which I agree are often too far apart, and take 3500 miles as a good time to change the (mineral) oil where the engine is subjected to *severe* service ... We are being advised by oil companies, whose interest is in selling more oil, not less, that with synthetic oil we can delay changes to 10,000 miles under the worst conditions of use.
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Dizzy - I can't disagree with much of that, although if "synthetics have little reaction to the products of combustion and they readily part with these products on passing through the filter" then they are going to clog it up sooner!
The oil companies' chief interest is in making money, and if they can do that by selling less oil at three times the price, I imagine that suits them very well.
I've nothing against synthetics, per se, but I do rather baulk at the price. I suspect that in most cases, a mineral oil changed twice as often (with a new filter) will preserve an engine at least as well, if not better...
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Tom,
My apologies - My reference to the Oil Bible site was intended for jc's attention rather than yours.
Rich
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