Switching Oils @ 120k miles

[2011e70]

I bought a 2011 E70 with the N55 engine.

The previous owner ran 5w40 synthetic its whole life, however I've never liked the idea of running oil that is not the manufacturer reco'd weight. For the N55 this is 0W-30, 5W-30, 0W-40, and 5W-30.

Is there any danger of switching from 5w40 to 5w30 synthetic @ 120k miles?

My gut tells me No, however these are finicky motors.

Thanks

[TwinSnailz]

Going to 30w will save you some fuel. Brings your oil up to operating temp faster. Circulate quicker on cold startup. May not cushion engine noise as well as thicker oil.
Remember all oil brand/manufacture have different specs even though they state the same weight.
Example:Castrol 0-40 is thicker than mobil 1 0-40
But mobil 1 has a slight higher HTHS.

[Sophisticated Redneck]

Originally Posted by 2011e70

I bought a 2011 E70 with the N55 engine up here in Canada.

The previous owner ran 5w40 synthetic its whole life, however I've never liked the idea of running oil that is not the manufacturer reco'd weight. For the N55 this is 0W-30, 5W-30, 0W-40, and 5W-30.

Is there any danger of switching from 5w40 to 5w30 synthetic @ 120k miles?

My gut tells me No, however these are finicky motors.

Thanks

I am big fan of 5-40 in the n63/s63 in warmer climates however for a n55 in Canada, it might be a little thick, I would reach out to a few oil companies like liqui moly and see what they recommend.

Please Take what BMW (and any car maker) recommends with the same conviction that you would give to relationship advice from a drunk friend who has been divorced five times.

BMW cares not about what happens to your drivetrain after 100k miles. If you don't believe me please check their recommendation on transmission oil change intervals.

All fluid recommendations are not direct from the BMW engineers, they are filtered by management first and are created to allow for maximum profit, meaning they must not contribute to failures during the warranty period and they must provide the maximum fuel efficiency for regulations and as a bonus for marketing purposes. Often these goals do not line up with longevity as that is not their main objective.

[X5 MAN]

Been using 0w-40 in my N63 all these years.

Perfect oil for cold winter(0) and hot summer(40)

[Thecastle]

Oil does multiple jobs in an engine including;
1) minimize friction / lubrication
2) engine cooling
3) ring sealing / sealing in general
4) protect against corrosion
5) engine cleaning

Having, the wrong viscosity oil (too high) means in tight tolerance areas there may not be sufficient oil flow to cool and lubricate parts correctly. As viscosity increases oil flow decreases (thicker and harder to pump) which also reduces heat transfer (decreased oil flow). I'd expect too high of a viscosity engine oil will increase the likelihood of rod bearing failure, as oil flow rate will be lower than designed in this tight clearance area and ability of the oil to cool the bearings decreases, increasing bearing expansion further decreasing film space and thus accelerating wear and heat.. Rod bearing failures seem to be the number one reason for premature the death of BMW 6/8 cylinder engines.

I doubt 5w-40 will be a problem for the engine as some brands its listed as okay with the S63. But it's unlikely to offer a measurable benefit compared to 5w-30 for engine longevity given its reduced heat transfer and reduced flow in tight clearance areas like turbo and crank bearings.

Most people go to thicker oils on worn engines, to improve ring and valve sealing to reduce burning and reduce noise on rod knock.