Your Oil Questions answered

Hi Simon,

It's a 1997 facelift model (with 100k miles).

Thanks

Carl

Hi Simon

I have a 2002 525d which will be doing 30k miles a year, mostly between Farnborough and Plymouth (50 - 80 mph, barely ticking over).  From your posts it looks like I can trust the main dealer to use a suitable oil (who I am obliged to use until the warranty runs out at the end of the year). 

My questions are a bit more general though.  I am new to diesel ownership and I carry a bunch of old wives tales about higher main bearing pressures, more soot etc., which mean dielsels require high spec oils. 

1. So - what demands do modern turbo diesel engines put on oils, compared to similar sized petrol ones? 

2. Given that my nominal oil change interval is the same as that for petrol engines, I presume modern oils are up to the challenge? 

Thanks for the good work,

Jim

Simon

My 1988 320i has 195000km (122000 miles) on the clock. I only drive it from April to November, in temperatures ranging from 10 to 35C.

I only use it at weekends etc, driving max 5000 miles per year. I am therefore concerned that the oil may drain back to the sump between uses, giving high wear of valve gear etc at start-up. I want an oil that will protect the engine under these circumstances - a reduction in absolute performance or fuel economy is not an issue. What grade and API category would you recommend ?

What kind of oil change regime would you recommend, taking into account the winter hibernation ?

Finally, do you have any views on Castrol High Mileage ? On paper it looks like a good idea for my engine, but is it really suitable ?

Thanks

Nick

Simon

I'm a bit confused. I thought a 5W-40 oil is 'thinner' than eg a 10W-40, and therefore more likely to drain down to the sump during long sits ? Sorry, but engine oils just confuse the hell out of me !!

Nick

Simon,

Reading this latest thread a few comments:-

1. As I recall there isn't Silkolene BMW LL-01 approved oil?  Am I right?

2. I should imagine after a day or 2 any oil of whatever grade will have drained back to the sump from a warm engine!

3. I seem to recall in last month's BMWCar magazine, a note from the editorial staff explaining that 10w-40 means that the oil is four times thicker at operating temperature than at start-up!!

Simon,

The point is they were, I recall, suggesting that the oil got thicker as it gets hotter!  Hence my surprise!!

You don't need to use Silkolene PRO S 5w-40 unless of course you want to put one of the best oils available in.

Fuchs Supersyn 5w-40 or Motul 8100 5w-40 are great fully syn oils and BMW Approved.

I would still use a fully synthetic 5w-40.

Just email me for a price list sales@opieoils.co.uk

Cheers

Simon

Simon

After yet more reading around on the Internet, daylight may be breaking through

A lot of BMW experts and Forums in Germany are saying that 0W-xx and 5W-xx oils are too 'watery' and therefore bad, and that an old E30 M20 engine needs at least 15-xx. But I'm starting to think they have misunderstood the viscosity ratings. This is what I think is really going on:-

The ideal viscosity for the engine is the one a correct oil reaches once the engine is at operating temperature - say about 100C, and this is best described by the second part of a multigrade designation. A xxW-40 oil will be at about 12-15 cSt at this temperature, and we can assume this is roughly what the BMW designers had in mind for a M20.

The first part of the designation is the cold behaviour of the oil, and by cold I am beginning to think we are talking about a non-warmed up engine ie anything less than 100C, whether that is a 10C spring morning or a -20C winter morning.

As all oils unfortunately become thicker as they get colder, in any non-warmed up engine the oil will be thicker than the optimum 12-15 cSt. This reduces oil flow and increases friction, both of which are bad for the engine. It will also lead to heat build-up, which is believed to be the main reason for cracked cylinder heads on M20s.

Therefore the best oil for an engine is one that has optimum viscosity at high temperatures (ie xxW/40 for an M20), but that doesn’t thicken up too much for my sunny spring morning trips. As a 5W-xx can still manage halfway decent flows at lower temperatures than a 15W-xx, a 5W-xx will be less overthickened at 10C than a 15W-xx. Overall there are no conditions in which a 05W-40 will be thinner an equal quality 15W-40, but the 05W-40 will be closer to optimum at engine start-up.

Looking at the Motul data sheets, 300V Competition 15W-50 is 18cSt at 100C, and 128cSt at 40C. At 100C it is therefore slightly over optimum, but as a full race engine will run warmer than a road car this is reasonable. But at 40C it is ten times thicker than optimum, and it will be even worse at 10C.

8100 X-cess 5W-40 is 14cSt at 100C, and 83cSt at 40C. At 100C it is in the  optimum range. At 40C it is only six times thicker than optimum, and so should also be better at 10C. Therefore the 8100 X-cess 5W-40 is the right oil for a summer only, weekend use M20 engine.

Simon, this leaves me with some questions:

1 - Have I understood correctly ??

2 - If I am right, wouldn’t the 8100 E-tech 0W-40 be even better ??

3 - If I am right, why does 10W-xx and 15W-xx exist any more, they offer no advantages over a 0W-xx ??

Thanks for being willing to give up your time to bring clarity to a murky subject

Nick

Hi Simon,

I have recently bought a 1987 525e with the M20 engine, it has 73k on the clock and I'm thinking about doing the first service on her as the gloop in the sump is very black. My requirements are similar to above, use only during spring/summer and generally using for long runs at the weekend. The engine is a torquey big beast and redlines at 4500rpm and my driving style is lazy cruise, so no high speed stuff needed! I also worry about wear from cold, always try to let my cars run for at least a couple of minutes before driving away. I'd be willing to spend a little extra to ensure good protection, so if you could advise possible oils that would be great.

On a BMW unrelated note, I also have an 83 Chevette(!) with 88k on the clock. The engine is good and tight and doesn't smoke at all, it's the standard little 1256 and I'm currently using Halfords cheapo 20W50 in it. Again it is never over-revved so performance or racing oil is not a consideration! I was just curious could you recommend an oil for this application? Want to make sure the engine stays as good as it is. Thanks for your help, it's a great service you provide!