Why does the N55 run so much hotter than the N54?

**B00STED** · 02-07-2017, 07:54 PM

In comprable temperatures, my N54 135i with the aux cooler hits 215 F after a 25 minute drive. When I was driving my family's 435i, it takes 15 minutes to hit 250 F. I actually don't mind the N55's quickness to reach operating temp, but why does the N54 take so much longer and, in my experience, stay much cooler than the N55? I went on a hour long drive with my 135i and it maxed out at 235 F.

**Stück** · 02-07-2017, 08:30 PM

It is running at the temperature BMW engineered it to.

**maxell0405** · 02-23-2017, 07:24 AM

I try not to chime in when I don't actually know the facts, but I suspect that your 135 has an oil cooler, especially if it a sports package car, and the 435 does not. The turbos are different and no doubt so are the aerodynamics. I think those oil temps are frightening, even though they are "normal" according to BMW. No oil formulator publishes numbers for temps that high (215 is not so scary as 250) - so you don't know what the oil properties are. If I had one of these cars I would run only a Group V oil and change it often, especially since I would be driving it pretty hard.

**pbonsalb** · 02-23-2017, 11:07 PM

That is my guess as well -- no proper oil cooler. Our 08 535xit with twin turbo N54 has one-- you can tell by the two hoses running off the oil filter housing.

You can add one but may not need to. Oil can run near 300 without issue if synthetic. Coolant under high pressure like some BMW expansion tank caps allow won't boil until 265F.

For hard core use, I'd mod to lower oil and coolant temps. But if all you do is the occasional highway pull or a 5 second romp here and there, you should not need more.