I live in South Jersey and I have been using Red Line Synthetic Motor Oil - 5W30 year round in my 1999 M3. However, I have been reading on other boards that I should be using a heavier weigh oil like 15W50 for the warmer months. Can anyone with an E36 M3 in this region chime in with opinions?

are you losing oil?

None at all.

15w-50 is heavy, i used it in mine last summer and had to let it warm up a bit longer. At any autozone store, the 15w-50 is labeled "diesel truck oil" although it will work fine. Seems like most people run anything under that except the guys who track their cars.

That is good to know. Thanks.

I use 0-40 currently. I've used other weights. All are fine, I just stick with full synthetic. I used to run like 15-w50 or 20w-50 in my last car in the summers, which was fine, but not really necessary

5w-30 colder months / 5w-40 warmer months