Someone tell me what oil to buy!!

[Grizo]

Have had my e30 for about 4 months now, looks like the oil light is just about to go on, I need to do my first oil change. From the service records it looks like it has had "c15w40b" from the dealer since day 1. I'm guessing that conventional. But there is so many contradicting threads about oil it's ridiculous. Someone just tell me what to buy so I can stop searching!

[DesktopDave]

I'd follow the owners manual, can't go wrong with that. Conventional oil is more than good enough for our cars.
 
IIRC for the M42, BMW specs conventional 10w40 for fall temperatures. In another three months/3000 miles or so, change to a thinner oil.
 
If you want to learn more about oil than you care to know, check out BITOG.
 
I'm not recommending this for anyone else, but in my 318i I stretch out my oil changes with synthetics. Please keep in mind that I have a high-mileage engine in a car that I don't need for work (just for a hobby). I also run used oil analysis and am willing to risk the occasional engine swap. That's the price I pay for a questing mind.
 
Anyhow, I've found that my little M42 can easily run extended oil changes to about 12K miles, as long as I keep filters changed every 6K miles or so. I've used Mobil1, Castrol, Quaker State and Havoline synthetics; tested everthing from 0w20 to 15w50. From the data I've collected, brand doesn't matter much. Wear metals seem the lowest with thicker 50-weight oils (yeah, I know, duh). But fuel mileage oddly seems to be best with 40 weights. I'm not 100% on that as I'm still short on data, but that's my current conclusion. I'd avoid the really thin oils, I noted no improvement in mileage and a measurable increase in wear metals, along with a few more drips in the driveway.
 
If you decide to try some synthetic, WalMart usually carries a 5-qt jug for about $30. That and a Mahle filter and I'm on my way.

[Grizo]

Did you notice any difference between synth and conv. oils? Like a 10w40 synth vs 10w40 conv?

[DesktopDave]

Yep - a slight increase in fuel mileage and the ability to run it for far longer, between similar viscosity oils.  But synthetics cost several times more, so it's not really a bargain.

[romkasponka]

Synthetic washes engines internals much better than conventional. If engine oil is clean after few thousand km it means it does not wash your engine internals and you collect carbon deposit inside your engine. P.S. that is my opinion from my personal experience. I am using for 5w50 (mobil probably for daily car and 10w60 Valvoline VR1 for my E30318is (200000km, engine rebuilded with new seals, piston ring with honed cylinders, 11:1 comp ratio) and after ~20000km I had to remove head for some custom work and all the internals was really clean like it was assembled few weeks ago...

IMHO if your climate zone include cold winters like -25C go for 5w40(or50). If its hot summers like +30C go for 10(or20)w60 if you love your car or you like to rev it till the limiter quite often

It can be semi-synthetic also, do not look at such things. Look at the viscosity characteristics like 10w60 5w50 and so on. When our car was made there was no such oils like 10w60 and now oils are with much wider  temp characteristics. You will not find mineral oil with wide temp characteristics.

[Grizo]

Synthetic washes engines internals much better than conventional. If engine oil is clean after few thousand km it means it does not wash your engine internals and you collect carbon deposit inside your engine. P.S. that is my opinion from my personal experience. I am using for 5w50 (mobil probably for daily car and 10w60 Valvoline VR1 for my E30318is (200000km, engine rebuilded with new seals, piston ring with honed cylinders, 11:1 comp ratio) and after ~20000km I had to remove head for some custom work and all the internals was really clean like it was assembled few weeks ago...

IMHO if your climate zone include cold winters like -25C go for 5w40(or50). If its hot summers like +30C go for 10(or20)w60 if you love your car or you like to rev it till the limiter quite often

It can be semi-synthetic also, do not look at such things. Look at the viscosity characteristics like 10w60 5w50 and so on. When our car was made there was no such oils like 10w60 and now oils are with much wider  temp characteristics. You will not find mineral oil with wide temp characteristics.

Did you get a power increase with the 11:1 comp? And yea its B.C. winter is coming up but I don't think I'll see anything less than -10C. Is there a big difference between 10w40 and 10w50?