Engine Oil for 2.0L M10 4cyl?

[meestapeta]

I recently purchased a '77 320i 4cyl (E21 chassis, M10 engine) So I figured I should change the oil in my car every once in a while, but the question is, what kind should I put in? As I understand Mobil 1 full synthetic is basically the best stuff out there, but the oil grade recommendations in the car's manual don't include any options for the temperature ranges I'll be working with. I live in Wisconsin so it could be under zero in the winter but also 90s in the summer. I ended up buying 10W-30 but now I'm having second thoughts. Does anyone have any ideas?

Thanks for your help.

[RealBMW 02]

you might want to go with something a little better suited for the winter months, a 5W-30 would probably be better. All automotive oils (well mostly all) are multi-grade oils meaning they meet the viscous requirements for two or more SAE (society of automotive engineers) grades. The W stands for winter and the number before the W is the viscosity of the oil at low temperatures. The number without a W is the weight at normal engine operating conditions.
So in other words, with 5W-30, at low temperatures, the oil will be thinner (noted by the smalled number 5) and at higer temperatures, the oil viscosity will be thicker so that the extra ambient heat will thin it out to where is should be.

You could also go with two different oils if the temperature change is really exsessive. In the winter months you could use a 5W-30 and in the summer, if you don't expect to see any cold temperatures and lots of extra hot days, then you could switch to a 10W-40 or 20W-50.

The last thing to take into consideration is the condition of your engine. If you suspect that your bearings and rocker shafts are worn, or if you think you have excessive blow by, then you might want to go with the heavier oil as it will help to seal up the excess clearances. However, while heavier oils give some extra protection to worn bearings and other loose engine parts, lighter oils are better for engines in good condition. Lighter oils actually reduce friction because they can flow more easily. This improves both fuel efficiency and engine life.

Hope this helps.
~Adam

[meestapeta]

Thanks for all of the advice, that helps a lot. Nice car you've got there by the way. Are you autocrossing in that picture? I autocrossed my old car (Datsun 280Z) once but I haven't been out in the 320i yet. From the impression it gives me on the street though it's going to be a dream to autocross it or take it to a track.