First inspection of Z4M throws up some issues, feedback appreciated

[jontZ4M]

Hi guys!

Please see pictures attached.

My 2006 Z4M Roadster arrived earlier this week. 2006 with 49k miles, 5 owners, just over £17k. Today was the first time I had a few hours to check her out properly. It would be really appreciated if you could read through my points below, I am completely new to BMW's.

1) I checked the oil filler cap and noticed white scum (see pic attached). Also white scum inside the spout that leads to the oil cap. Looking into the top of the cams, no obvious white there. My understanding is this means water in the oil. It may simply be that the car hasn't been used much and has been sitting outside, however I figured it was worth investigating further in case of HG issues. No obvious exhaust smoke. I decided to do a simple cylinder compression test to check for any problems. I got stuck at trying to remove spark plugs. My normal 5/8" spark socket did not fit the plugs. Not sure why. Are these 16mm spark plugs or 14mm please? I wonder if anyone can please point me to a removal socket that fits these plugs?

2) Exhaust is leaking/blowing just before what looks like 2 x catalysts. Entire exhaust looks pretty tired, will remove and examine. TBH standard exhaust seems much to quiet for me, I would prefer something a lot louder and more obnoxious. Can anyone recommend a nice stainless system with some good volume please? What is the etiquette for these cars? Do you just replace rear sections? Do you do decats? Manifolds? I'm guessing no useful power gains to be had here? At first glance S54 seems to be pretty much maxed out in standard trim.

3) For such a low miles car I was surprised to see so much rust on the underside. I come from 90's Jap cars so I am use to it. I've raised the car and intend to remove all of the various underside panels to investigate the problem further. Will create a plan when I know the extent.

4) The rear diff is leaking fluid. Appears to be from the front seal. This is annoying... Is this a typical problem found on Z4M? What would you recommend as a course of action for this please?

5) At front of engine bay is a large black metal assembly that houses rad/AC condenser etc. This is too rusty for my liking. My first instinct is to remove it and restore it. Is this assembly just bolted or also welded do we know? Any dangers here that we know of here? Rad area looks quite delicate.

6) Please see 4.jpg attached. What the devil is this ugly cylinder thing doing here? Can I remove it without serious consequence? Also while exploring there rear underside I noticed between the two mufflers hugging the chassis is big plastic black cylinder about 12" long. Any idea what this does?

General findings:
- the engineering in these cars looks pretty top notch.
- gutted about rust issues, but we'll overcome.
- I'm fighting my way through various plates, covers and braces underneath the car, trying to get to the exhaust. Why are these covers/braces here? I've never had a car that has these. I guess they all have to go back on afterwards?

Thanks for reading! I am looking forward to me next session on the car!

Jon

[Jon2215]

Hi Jon
The canister is the secondary air pump,only runs when engine is stone cold for a few minutes.
The oil mayonnaise may just be due to short engine start ups and it not getting up to temperature to burn of condensation.
Plugs iirc require a 14mm socket.
My M runs Eisemann rear boxes,not too loud but have a great rasp that doesn’t over come my CSL airbox.

Jon

[pvr]

Rust underneath usually is if the car has lived outside near the sea or in Scotland.

[flimper]

Diff seal leak is very common, mine been doing it for at least 5 years without issue, but am getting it sorted in a few weeks

[Adam D]

4) if the full number plate is what I suspect it is (the motif is fairly unique and google throws up a similar car recently for sale) then a diff oil leak was mentioned on the last MOT - any warranty to get the diff input seal changed as a fault at point of sale (normally that’s the one which can weep).

Rust. I have a 2007 Z4M and it’s quite good underneath for its age, the rear exhaust silencer couplings did need replacing but the mid pipe was in decent condition. Some of the nuts were a bit rusty but the cross braces looked only moderately tarnished considering the vehicles age. My car lives in a garage which may help.

[bigwinn]

Where was it purchased from (if you don’t mind saying) and did you have a good crawl over it before parting with the cash?

[Mr Tidy]

Firstly congratulations on acquiring your Z4M Jon.

I'd give it a decent drive and if there is no more mayo that's an easy fix!

My car is quite rusty underneath, but it's just had it's 16th birthday so I think it just goes with the territory.

If you car is anywhere close to needing an Inspection 2 service that would be a convenient time to get the diff oil seal replaced because that service includes fresh diff oil.

My car came with Powerflow back boxes and they give a handy increase in volume without droning, but I've read good things about RPI and Supersprint ones too.

[plenty]

The flanges connecting back boxes to Y-pipe always corrode beyond repair. New flanges are available from BMW, or you can dispense with the flanges and use sleeves or U-clamps over the joints.

It's not as common for the flanged ends connecting Y-pipe to cats to be damaged. Might just need new gaskets. Make sure to get new bolts as the old ones will inevitably not be reusable.

I've got a cheap catback exhaust for sale in the classified section on here, that's a bit louder than OEM without being obnoxious.

[MKZ4000]

The gunk on the cap looks very minor and much more likely to be cold weather and short journeys.

I’d still do a sniffer or compression test to ease your mind.

Any pics of the underside / rust ?

[grannyknot]

The z4m is looking good, the front seal on ours diffs leak and it is a fairly involved job to change it.
A lot of owners leave it, just be sure to top up the diff oil every year or so.
The secondary air pump, useless. Most owners over here pull and dump it in the bin, it robs a bit of power.
You just have to cover the air pump opening on the cylinder head, block off plates aren't difficult to find.
Looking forward to more pics.

[craig3.2]

As others have said,all common things on the z4/m.

1. Never had the "mayo" on my M, but did have it for a short spell on my 3.0, when I started using it briefly for short journeys,as it obviously wasn't getting getting long enough a run to burn it off,as mentioned. A few weeks later,no longer using it for short,5 minute runs,it was all good again. Orthers at the time had similar findings (circa 2010).

2 & 3. Ruat on Exhaust system/underneath is common, especially as these cars are 14 to 16 years old. It will depend on what Country climate conditions are where the cars been.....any seaside town will make this worse obviously,but most places in the UK will have an effect,if it's ever been used in winter.

Backboxes and hangers/supports corrode.
After market hangers available online.
Mine recently rusted just at Cats
Cats are Expensive,from BMW or Aftermarket,and not many options if u need to renew them.
A few good choices of Exhausts....Eisenman,Remus,etc etc.

4.Diff leaks are common too
Main Diff seal usually is the culprit, although rear two(Left and Right) can go too,so worth doing All 3 when stripping it Apart.
The Original BMW Diff Oil is Expensive (£100), but apparently has Additional properties or something in it that other diff oils don't(that came from Redish Motorsport).
Personally,I wouldn't leave a Leaking diff.
Why not get it by fixed? It's a £300-£500 job, depending where you take it,Inc the BMW diff oil,and All 3 seals

[Argenta]

The secondary air pump, useless. Most owners over here pull and dump it in the bin, it robs a bit of power.

Fake news.. It does NOT rob power but injects air the first minute when the engine is stone cold, then it's inactive.
However - I've tried disconneting it, starting in a (very big) garage buliding. I could not believe how bad the exhaust fumes were without it.. I had to leave the building.
So, it does a very good job. (Hence why BMW put it there).

[N4LLY]

What short journey's and cold weather does to your oil. See here.....

https://video.citnow.com/vp2sYS2CgTU

[buzyg]

Welcome to the forum, great looking ///MR.

The exhausts flanges fail between the back box and the mid section. I had mine sleeved simple enough at a decent exhaust shop.

The diff seal is indeed a common issue. Again simple enough, so my mech told me. Done while the exhaust was off being sleeved and timed nicely as the diff oil was due for a refresh any way.

Enjoy your Car.

Oh and don't be too obnoxious.

[grannyknot]

The secondary air pump, useless. Most owners over here pull and dump it in the bin, it robs a bit of power.

Fake news.. It does NOT rob power but injects air the first minute when the engine is stone cold, then it's inactive.
However - I've tried disconneting it, starting in a (very big) garage buliding. I could not believe how bad the exhaust fumes were without it.. I had to leave the building.
So, it does a very good job. (Hence why BMW put it there).

It is not fake and it is not news.
The secondary air pump system adds extra weight which uses up power, it also is an electrical draw that uses power, it creates turbulence in the exhaust flow which robs power.
Granted, removing it doesn't free up a lot of power which is why I used the phase, "a bit of power".
The OP asked

Can I remove it without serious consequence?

and my opinion is yes you can. I believe is useless because here is the consequence of removing SAPS, you let X amount of unspent gas into the atmosphere or you burn X amount of extra fuel to run and carry the SAPS in the first place, it is a zero sum game.
It allows the politicians to appear as if they are doing something and lets drivers feel virtuous, when in reality neither are true.

I'm not arguing that SAPS doesn't do its job very well because it does, I just don't agree that it is needed, The Emperor's new clothing comes to mind.
Sorry for the rant.