Why Syn oil?

[WVMTNBIKER]

Though I've used Mobil 1 fully syn oil in a LOT of my vehicles i.e Corvettes, MB's, Volvo and others, WHY exactly do I have to use fully SYNTHETIC oil in my '03 X5 3.0i manual shift? I know it's factory recommended, but seems to me that an engine with 80K miles would require maybe a thicker dyno oil rather than syn oil(though mine has ZERO oil leaks anywhere).
I mean it's no problem to use it b/c I change my own oil, just curious to know if I could use a high grade dyno oil i.e. Castrol, Penzoil etc?

[rph74]

Good question. I don't know exactly why, but I would stick with the factory recommendation. I have used Mobil 1 in my E39 for the last 7 years, only to find out recently that it was unapproved oil. My understanding of the approved oils is that it allows for longer service intervals.
In the end, my recent research has led me to simply buying the OEM BMW 5W30 from the dealer. At $5.69 per quart, it is a bargain compared to the Mobil 1 OW40 that sells for $7.49 per quart. The Ow40 is the only "approved" oil that I can easily find in my area.

Here is the list of approved oils according the BMW:


BMW North America

[FSETH]

Originally Posted by rph74

I have used Mobil 1 in my E39 for the last 7 years, only to find out recently that it was unapproved oil. My understanding of the approved oils is that it allows for longer service intervals.
In the end, my recent research has led me to simply buying the OEM BMW 5W30 from the dealer. At $5.69 per quart, it is a bargain compared to the Mobil 1 OW40 that sells for $7.49 per quart. The Ow40 is the only "approved" oil that I can easily find in my area.

Here is the list of approved oils according the BMW:


BMW North America

Check out this thread. Specifically JCL's post #26 and later regarding BMW's dated LL-01 standards.


http://www.xoutpost.com/bmw-sav-foru...ngine-oil.html

[JCL]

Originally Posted by WVMTNBIKER

Though I've used Mobil 1 fully syn oil in a LOT of my vehicles i.e Corvettes, MB's, Volvo and others, WHY exactly do I have to use fully SYNTHETIC oil in my '03 X5 3.0i manual shift? I know it's factory recommended, but seems to me that an engine with 80K miles would require maybe a thicker dino oil rather than syn oil (though mine has ZERO oil leaks anywhere).
I mean it's no problem to use it b/c I change my own oil, just curious to know if I could use a high grade dino oil i.e. Castrol, Penzoil etc?

I think you are mixing up two separate issues, the thickness of the oil (or weight) and the lubricating performance of the oil. Both traditional (mineral) oils and synthetic oils come in a variety of weights, or viscosities. A heavier oil (which you are associating with fewer leaks) is also less likely to get past the piston rings (which would have been a factor in old engines many years ago, so heavier oils were used at higher mileages). Neither of those factors are particularly beneficial with modern pistons and rings at your mileage. A heavier oil can cause damage because it can't lubricate in all the fine passages in a modern engine designed for an oil such as a 30 weight (the second number, in 5W-30). Incidentally, dino oil (presumably oil that came from dinosaurs) is a misnomer, since lots of synthetics are made out of traditional base stocks, but use a synthetic process to improve the base stock) so dinosaurs gave up their lives for most of the oil we buy.

Synthetics are often specified by manufacturers for two key reasons:

• They are more stable with respect to shear, ie they don't break down and get thinner over time, they maintain their specified viscosity better (including at high and low temperatures)
• They are more resistant to oxidation, which means fewer issues with sludge and oil breakdown

Those factors mean that they are good in hot or cold extreme ambients, that they last longer, and they permit longer oil change intervals. They are all relating to the quality of the oil in terms of it still being fit for use.

If you were going to change your oil very often, like every 5000 or 6000 miles, you could probably get away with a traditional mineral oil, particularly if you had reasonable operating temperatures, little city/traffic driving, etc. It would lubricate fine, it just wouldn't maintain its properties as long. However, since you can get high performance oils that do last the full change cycle, for not much more money, they make sense.

Fully synthetic just means that it isn't a percent of synthetic oil mixed with traditional mineral oil (ie 50:50). It doesn't mean which synthetic process is used to make the oil, or which base stock it comes from, so any synthetic oil is fine. What is most important is that it meets an API-SM specification. There may be traditional mineral oils that meet that spec, but I am not familiar with which ones. Your model year likely specified an API-SJ oil, and current specifications are quite a bit better than that.

[WVMTNBIKER]

Very nice indeed, sir. I mostly realized the bulk of what you said regarding the syn process vs dino oil/mineral oils. That's why I've used Mobil 1 in a LOT of cars.
I was curious if an '03 model would still require syn oil. I liked your statements about piston rings vs heavy oil. Never thought of it that way I guess.
I always knew that syn oil was great stuff and it's breakdown properties were much better than conventional motor oil.
So it does make good sense to stay with syn oils and what BMW recommends to use. Few the few dollars difference in cost, in the longrun syn oils are superior.
Thanks for all the good info, guys. Much appreciated.
You will find me on here a lot with a lot of questions. Once I get into something, I really dive in.
So thanks for taking the time, and a lot of it, to help me discern the differences.