Preventative maintenance advice

[DeutschRennfahrer]

I recently had to replace most of my Z4's cooling system which has me wanting to cover all preventative maintenance to avoid costly repairs. My car now has 120k miles and I'd like to keep it running reliably for a while longer. Here's what I've replaced in the last year:

Water pump, thermostat, and coolant reservoir.
Lower front control arm bushings
Belt and belt tensioner
Valve cover gasket
Spark plugs
Cabin air filter

What are the common failure points that I've not already addressed? Let's hear your stories.

[gpraceman]

Have you changed out your transmission and differential fluids? While they are supposed to be "lifetime" fluids for non-M's, they really should be changed out as those fluids will pickup contaminants and degrade from heat over time. On my M, I am changing out all of my fluids.

Rebuilding the VANOS may be something that you want to tackle. If that grenades, there goes your engine. Though, I am not sure just how much of an issue that is with non-M's.

[Efthreeoh]

I have an '06 E90 325i with the N52 in it. That engine has 350,000 miles on it. I've had the car since new, so I can reasonably say I have experience keeping an N52 in good shape. N52 doesn't really need a lot of maintenance and does well with long oil change intervals if one uses BMW spec LL01 oil and an OE or OEM MANN oil filter.

Your list of replacement parts as maintenance is pretty much complete for 120,000 miles. You didn't mention the engine air filter, which should be changed every 3rd oil change or about every 45,000 miles. Also, the N52 will leak oil at the Oil Filter Housing Gasket (OFHG). The OFHG can leak oil onto the serpentine belt and cause it to slip off the pulleys. In rare situations the OFHG can leak coolant into the oil system, but it's a rare occurrence. gpraceman suggests changing the transmission and differential oils, which is good advice. You can change them as far as 100,000-mile intervals, so if they've not been changed that you know of, then change them at your next service interval.

What I'm not sure about gpaceman's advice is "rebuilding the VANOS". What some N52 owners do (me included - I actually first suggested it years ago on the E90 Forum) is clean and swap the VANOS solenoids periodically. I recommend every 50,000 miles. My recommendation has no science behind it other than the interval is easy to remember. There is a good DIY on the E90 Forum DIY section regarding VANOS maintenance. The E90 Post DIY section has a lot of N52 maintenance content that you can use as a resource your N52 Z4. The N52 in the Z4 3.0si has Valvetronic, VANOS, and 3-stage intake manifold (see below).

What gpaceman may be talking about are the 3-stage intake manifold DISA valves. There are two DISA valves in the N52 in the Z4. DISA is a German acronym for “Differenzierte Sauganlage”. The DISA valves adjust the intake manifold intake runner lengths to improve torque output at varying engine load situations. The DISA valves in some BMW engines, the N52 included, are known as a weak part and can break in higher mileages (over 80,000). When a DISA valve fails, and depending on how it fails, it can send broken pieces, both plastic and sometimes metal, into the engine cylinders. If the engine starts to run poorly and fuel consumption greatly changes, those are signs of a bad DISA valve(s). If the metal shaft that the DISA valve butterfly rides on dislodges from the valve body it can pass into the cylinder and damage the engine; it's a rare event. The intake manifold needs to be removed from the engine to replace the valves and the valves are a bit pricey.

At some point the N52 oil pan gasket starts to leak. On the E90, it requires a subframe drop. On the Z4 it may be easier to replace and not require a subfame drop. I've done the pan gasket on my E90, which is an involved DIY to say the least. The Z4 looks to be a bit more roomy underneath than the E90 is. The pan usually starts to weep at the right rear corner near the bell housing. You can let it weep like that for a long time before it ever gets to the point that the gasket needs replacement.

[3798j]

Brake fluid is hydroscopic (it absorbs moisture), every two years it's recommended to do a brake flush with fresh DOT 4. It's a good preventative service procedure that should increase the life of the master cylinder and calipers.

[elerner61]

Originally Posted by 3798j

Brake fluid is hydroscopic (it absorbs moisture), every two years it's recommended to do a brake flush with fresh DOT 4. It's a good preventative service procedure that should increase the life of the master cylinder and calipers.

Hygroscopic

One item that comes to mind that would leave you by the side of the road is the alternator. If it hasn't been replaced by 120,000 it could start to fail or just outright die any day. You could replace just the voltage regulator which would give you new electronics and brushes at a much lower cost.

[3798j]

Originally Posted by elerner61

Hygroscopic

Whoops!

[WAMz4]

My car just hit 100000 miles in June and I have replaced most everything on your list. Definitely check the oil filter housing gaskets, there are 2 of them, and if they start leaking oil will drip on the new belts and hoses.
Its an east DIY if you have the right tools -
https://www.youtube.com/watch?v=IORcQabnoIw&t=1845s

[gpraceman]

Originally Posted by Efthreeoh

What I'm not sure about gpaceman's advice is "rebuilding the VANOS".

I'll defer to someone that has experience with the N52 engine. I've got the S54 engine and the VANOS is certainly an issue to address at some point with it.