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Hey all!
I recently had my oil changed and the shop recommended a few things. My father was a mechanic by trade and as such, I've done plenty of car work myself (converted an E46 to electric in college) so I was skeptical. I've mainly gained knowledge on American cars, figured I'd consult people who know this car better than I do.

The shop recommended three things, two which they could actually perform.
- Coolant Flush
- Transmission Service (maybe fluid flush? they can't do it anyways...)
- Differential Fluid

They also showed me the oil fill cap and claimed there was moisture, potentially indicating the a bad head gasket. I should've taken a photo at that time; if they didn't clean it, I'll add a photo for a sanity check.

The car has 106k miles on it and was owned by an older couple who seemed to 'blank check' most of the maintenance. Are these items that should be taken care of at this mileage or problematic with these cars? If so, they ballparked ~$100 for the diff fluid and ~$100 for the coolant flush, curious if that's seriously up-charged at all.

And a note about the head gasket topic. This car has never had any sort of smoke on start up, never had oil discoloration on the dipstick, and the motor honestly runs cold rather than hot. I made a post a few weeks ago mentioning that the temp gauge usually reads below the 'middle point' during longer highway drives or cooler areas. Other than the cap 'contaminants', all other signs don't seem to support their claim IMHO.

Figured I'd get some opinions and know what to ask for in more detail, let me know what y'all think!

*attaching photo because i can't stop taking pictures of this car*

Every time I bought a "new" used car, I would do this:
- all fluids (oil - engine, transmission, differential and breaks)
- new filters
- new spark plugs and if needed new wires

So, preventive maintenance is always good. Regarding your issue with the temp gauge, I would say go with the thermostat, it is easy to change and maybe it is stuck.

Regarding, moisture on the oil cap, perfectly normal, if the car sits a lot, it can moist up, and if you are in a moist area, then it will be normal. For example, I usually take my Z4 for weekend runs, sometimes it sits under the cover for a couple of weeks, and moisture can build up in the exhaust pipes and in the cap.

I think nothing is wrong with your Z4.

Btw beautiful color

Garage desperately touting for work. Run, run away.

Coolant flush. Pointless unless there's an underlying problem with corrosion somewhere, in which case that would need solving first. The days of cooling systems getting rusty sludge in them as a matter of course are long gone.

Diff oil: Unless it's got water in for some reason, it'll be ok. I've done mine before now on cars because it's an easy & cheap DIY job but it wasn't essential. Unlike an old Land Rover I used to run that generated green/grey goo in its axles.

Head gasket. There's nothing wrong with it. Like a lot of understressed engines, the M54 is prone to a bit of mayo if it's not got hot through from short journeys.

Tranny fluid: If it's a manual, see diff oil. If it's an auto, then there's many, many threads on the subject. The ZF box has a service schedule of about 60k miles according to the manufacturer but it's a lifetime fill according to BMW.

If anything this (and a new filter) is the important one. I find it hilarious the garage says it can't do it (I've done several myself as a DIYer quite happily.) People do say they've had the fluid changed and then the gearbox has exploded but I think that because the only reason they've had a fluid change is because the box is showing signs of failure and nothing would prevent it. Autobox fluid always comes out looking manky at this age so fresh fluid and filter can only be a good thing.

Brake fluid change would be wise if it hasn't been done for a while.

BMW want it done every 2 years and is one of the only things they seem really anal about.

Good point, well made. Brake fluid does age so is never a bad thing to do.

zriha wrote: ↑Fri May 26, 2023 10:21 am Every time I bought a "new" used car, I would do this:

I'll look into this, sadly no garage now that I've moved into a complex so I'll have to see what some of the non-trivial items would run from a real shop.

zriha wrote: ↑Fri May 26, 2023 10:21 am perfectly normal, if the car sits a lot

Previous owners were WFH during COVID and with 2 kids this car sat while the SUV got all the miles. This was my hunch, I'll keep an eye on it to see if it ever improves or worsens.

smorris_12 wrote: ↑Fri May 26, 2023 10:31 am unless there's an underlying problem with corrosion somewhere

System is in great shape from my own inspection. I was curious if these had the same coolant expansion tank issues like the E46's and if the flush was at all related. Another thing I'll monitor over the coming months.

smorris_12 wrote: ↑Fri May 26, 2023 10:31 am If it's a manual, see diff oil

5spd manual I'll ask local shops to see if they have their own experience/opinions on the necessity of a fluid procedure.

Usel wrote: ↑Fri May 26, 2023 9:59 pm Brake fluid change

Intriguing. I'll check on this, it's a great car for the mountain roads near me and having a good set of brakes is an area I believe deserves some focus.
I've been toying with the idea of brake/tire upgrades; not set on any path yet. Recommendations welcome!

zriha wrote: ↑Fri May 26, 2023 10:21 am Btw beautiful color

Thank you! Seems like we're aligned that Titanium Silver Metallic is a classy color for this gorgeous roadster.

Check out this video on how one person changed fluids - https://www.youtube.com/watch?v=BcULW_T3VHk

Opinions may vary, but at about 89K miles and sixteen years, I changed out my diff and manual transmission fluids. I had very slim maintenance records when I bought my car with about 80K miles. The diff fluid was clear amber - almost as clean as the new fluid. The MT fluid was more grey than I would have liked, so I was happy that I changed it.

The diff on my 2006 is a single-port case, so it's "pump out" and refill. For the transmission I bought new drain and fill plugs just to be safe. I used OE fluids, and the shifting is definitely better.