What oil....?

[araine901]

Are you saying that in the summer here in Phoenix when it does not get below 100 F (even at night) and is over 110 most days that 10-30 or 0-40 is just as good as 15-50? Just currious.

[SRR2]

Well what's the operating temperature of your engine when it's 80F? Say 220F. And what is it when it's 115F outside? Oh, 220F. Of course, you're going to be pulling a lot more air through the radiator at 115F, but the engine oil doesn't know anything about it.

BTW, if you have an E39 with the 7.2 or higher Motronic, the electric thermostat actually *lowers* the engine operating temperature in high ambients like yours.

Look at BMW's current oil recommendations. 5W-30 quality synthetic for most models (dunno about M-cars) for ALL TEMPERATURES!!

[araine901]

Well what's the operating temperature of your engine when it's 80F? Say 220F. And what is it when it's 115F outside? Oh, 220F. Of course, you're going to be pulling a lot more air through the radiator at 115F, but the engine oil doesn't know anything about it.

BTW, if you have an E39 with the 7.2 or higher Motronic, the electric thermostat actually *lowers* the engine operating temperature in high ambients like yours.

Look at BMW's current oil recommendations. 5W-30 quality synthetic for most models (dunno about M-cars) for ALL TEMPERATURES!!

Point taken. I am used to feeding my (air cooled) 911 15-50 M1 so I was feeding the 540 the same thing during the summer. Probibly overkill, but I feel guilty when its 117 out and I am running the A/C full blast and sitting in traffic.