Z4. 6Cylinder most reliable engine.

[Andrew13]

hi there
i’m new member in this forum, god bless you all !
planning to buy e85 or e86 (2005+ ULeZ Free), could you tell me please which engine i have to avoid based on your practice.
Z4 will be my first car in UK so i guess 3.0 insurance gonna be super high for me, this is the reason i’m asking from this trio 2.0 2.2 2.5 which engine is with less headache.
thanks a lot beforehand

 

[Chris_D]

why not shop around for insurance on a 3.0i before you write it off as a non option?
The 3.0i is the one to go for every time imo.
I tested many 2.5's and 3.0's before I realised there was no way I would ever want a 2.5 or smaller capacity. The power delivery is chalk and cheese in the M54 variant.
The difference between the 3.0 M54 and N52 is negligible and only really apparent when you're proper hammering it. The N52 has the edge and a bit more power but the M54 is a relatively 'simpler' engine. Plus it has a dipstick and mechanical waterpump which won't go pop at a momen't notice and put you at immediate risk of overheating/head warping disaster like the N52 will.
I went for an M54 mainly because it's a development of the bombproof M52TU of which I put many many many miles on.

 

[Zedebee]

I disagree with the above. The extra power in the 3.0 is certainly tangible, but the 2.5 is perfectly decent. It depends what you are used to and what you want. Stick with a 6-cylinder as it’s what differentiates Z4 from the herd.

If you must have a ULEZ engine, then the older, simpler, bombproof M54 engine is out. The N46 2.0l has more reliability issues than the 6-cylinder engines, but may be cheaper to run/insure if it doesn’t break. Which leaves you with the N52 in 2.5i (replacing the older 2.2), 2.5Si and 3.0Si. Of these the 2.5i is slightly less complicated but considerably less powerful. The later N52K “black top” engines had some reliability improvements over the earlier N52 “silver top” variant. All the M54 and N52 engines have a good reliability record.

The Z4 is remarkably (even bizarrely) cheap to insure, so don’t discount a 3.0i thinking it will be too expensive. I don’t know whereabouts on the insurance spectrum you are but I pay about £120 with Saga because I’m old enough; whereas my 19 year old insured his 2.5 for about £800 with Admiral. To insure a Hyundai i10 would have cost him £2k, go figure.

 

[tiglon]

If the consensus is that the 'N-54' is the best engine choice, can somebody explain which year of manufacture, and model which is considered the most trouble free.

I agree with this guy

 

[Mike6]

I have been very happy with my 2005 2.5 SE six cylinder. You could pick up the facelift 2006 2.5 SE for not much more money but when I was researching which one to buy I was advised against the facelift version as it had a fairly puny power output compared to mine albeit it has 6 gears against my 5. This was due to the introduction of the SI versions around that time.
Personally I wouldnt bother with the 2.0 or 2.2 litre cars.
Stick with the 2.5 or 3.0 which has good service history, no crash damage and moderate mileage and I dont think you can go wrong.

 

[Enigmatik]

At the end of the day, all the engines will have pro's and cons. What makes the difference is buying one that has been looked after. I tried 2.0, 2.5si, 3.0 and ended up buying a 2.5 (not the engine I'd have gone for ideally) because the rest of the car appeared to have been cared for at some point before the owner I bought it from.

Checking for service history, money spent on it, the usual suspects for each engine having been addressed at some point in its life. If you turn up and it looks rough, then I think most folk would walk away. They were slightly more expensive cars new, they will have similar bills now. If you turn up and it's got cheap tyres, have costs been cut else where. Regular fails in mot history likewise. Oil leaks and mechanical stuff can be worked on and make good bargaining points, plus you get to know your car. None of the non M sixes ( as you seem to be looking at non M cars) seem to have catastrophic failure issues as long you treat them to good oil and address issues as they arise.

Take someone with you for second opinion, try a few, if you can borrow or maybe invest in a code scanner as some issues can show up there but not throw a warning light. If looking at face lifts, check procedure for checking the oil (it's a pain). If oil is low check if owner has oil they use to top up, see what type they use.

Buy on condition, buy a car that feels right for you. Most of the above suggestions are based on fact I didn't do enough research/investigation of car I bought and stuff I'd check on next one. However I've been lucky, plus learnt stuff from this forum and carried out some work to get mine up to scratch.

 

[Mr Tidy]

Welcome to the forum Andrew.

Plenty of good advice on here already, but what you have had an what you want may have a bearing. There are 2 litre owners on here who are happy with their cars but for me a straight 6 engine was one of the Z4s unique features, and they seem to suffer less problems than the 4s.

Pre-facelifts have the M54 engine in 2.2, 2.5 and 3.0 litre sizes. Running costs are pretty much the same whichever you chose although only the 3 litre had a 6 speed gearbox, which may be handy if you expect to do longer trips.

Facelifts have the N52 engine in 2.5i, 2.5Si and 3.0Si flavours and again running costs for any of them are much the same but they all have a 6 speed box. The 2.5i was effectively a replacement for the earlier 2.2i but the N52s are all a bit more powerful than the pre-facelift equivalents. But facelifts came in SE and Sport trim levels and the Sport models came with a few modifications including M-Sport seats as standard (a red pair of those just sold on here for £600 which was cheaper than most).

All of the 6s can easily cope with higher mileages but as has been said the N52 in the facelifts has an electric water pump that will die at some point, typically causing overheating in less than a mile. When that will happen seems to be anyones guess - my first E86 needed a new one at 60K miles but my next one seemed to be on the original when I sold it at 91K. Apart from being stranded when it happens a new pump from Pierburg the OE supplier costs around £300 (or £500+ if you buy from BMW) but the N52s rev a bit higher with a bit more power as a bonus. While the N52 has no physical dip-stick, pressing a button on the dashboard will display the oil level so you don't need to get your hands dirty!

Now you just need to find the right one.

 

[Mike6]

Mr Tidy, you say that all N52 engines have more power than their pre facelift versions, at least I think that is what you are saying. But my 2005 2.5i SE has around 190 bhp whereas the equivalent 2006 facelift version has around 178 bhp albeit with six gears. I thought that makes it very underpowered for a 2.5 six cylinder engine.

 

[Enigmatik]

Think me Tidy meant model equivalent, as he said the 2.5 replaced the earlier 2.2 as lowest power 6cyl. Think 170 v 177bhp and probably better torque. The 2.5si would be next 6cyl up with 214/218 bhp or something via 190. 2.2 = 2.5, 2.5 = 2.5si, 3.0 = 3.0 and 3.0si added as range topper. You don't get a 2.2 n52.

Theory is adding the 3 stage manifold from the si model to the no si model and a remap will get you the missing power.

 

[Mr Tidy]

Thanks Enigmatic, that is what I meant.

By all accounts the M54s can happily rack up high mileages, although the only one I had I sold at 103K (it was in a 3 Series Compact not a Z4).

But N52s don't have issues at higher miles. I had an E91 325i that I sold on 139K and currently have an E90 330i that has done 120K. Both N52 engines and both still running strongly.

 

[Zedebee]

The 2.5si would be next 6cyl up with 214/218 bhp or something via 190. 2.2 = 2.5, 2.5 = 2.5si, 3.0 = 3.0 and 3.0si added as range topper. You don't get a 2.2 n52.

No straight 3.0 N52 in the UK either, so the 3.0Si (265bhp) replaced the outgoing M54 3.0i (231bhp).

 

[Enigmatik]

The 2.5si would be next 6cyl up with 214/218 bhp or something via 190. 2.2 = 2.5, 2.5 = 2.5si, 3.0 = 3.0 and 3.0si added as range topper. You don't get a 2.2 n52.

No straight 3.0 N52 in the UK either, so the 3.0Si (265bhp) replaced the outgoing M54 3.0i (231bhp).

Did not know that! Learn something everyday, so any face lift 3.0 is a 3.0si? Interesting to know for the future.

 

[Zedebee]

Did not know that! Learn something everyday, so any face lift 3.0 is a 3.0si? Interesting to know for the future.

True for the Z4. There may be a non-Si 3.0 in other applications, I don’t know.

 

[wiseguy]

I've put 115,000 of the 145,000 miles on my Z4 3.0si with no unusual engine issues. Fixing oil leaks and replacing worn out coil packs (aka, ignition coils) are the biggest things I've done. Change all the coil packs before they die, as the car runs terribly when even one goes bad. It's not an expensive fix and well worth it (make it part of your preventative maintenance).

My Toyota is no different. One bad coil pack and the engine indicates a cylinder misfire and runs terribly.

 

[Zedebee]

If you must have a ULEZ engine, then the older, simpler, bombproof M54 engine is out.

I was talking nonsense. Have just checked my ‘03 3 litre auto, which must be the most polluting of all the E85/E86 variants, and it is ULEZ compliant so it is a fair assumption that they all are.

 

[tug]

WHAT A LOAD OF OLD PESH! Everybody & their dog knows the N46 2.0 is by far the most superior variant ever made & is far better lookin than all the others. :evil:

 

[enuff_zed]

WHAT A LOAD OF OLD PESH! Everybody & their dog knows the N46 2.0 is by far the most superior variant ever made & is far better lookin than all the others. :evil:

Mate, when you change the coolant you’re supposed to throw the old stuff away, not drink it.
Mind you, using this old 4-pot as a daily and having sorted the various EML issues I have to say the handling is much more balanced.
Still sounds rubbish though

 

[tug]

Don't ya think so Mate? it might not crackle & burble but thats only because its more superior. I also think that the single exhaust oval tip looks by far more appealing than the double pipes with chrome tips on the lesser models.

 

[enuff_zed]

Did a run out to North Norfolk last year with Jock156 leading in his 2.0. Interesting to see the way he pups maintain momentum through roundabouts etc while all the bigger engined ones were brake and accelerate to catch back up with him.

 

[smorris_12]

Did a run out to North Norfolk last year with Jock156 leading in his 2.0. Interesting to see the way he pups maintain momentum through roundabouts etc while all the bigger engined ones were brake and accelerate to catch back up with him.

This is definitely a thing and far more fun than straight line acceleration. I've had a 320d Touring since the Kaiser was a lad and often wondered if I shouldn't have got the 3.0. I put the equivalent of sports suspension on it but put convertible anti roll bars on it and it changes direction like a fly. Many a time I've blatted it around the place and wondered if I'd actually be able to use any more power without attracting attention of Plod or punching a hole in the scenery.

I got my 2.5si Z as I really fancied a 6 pot but didn't feel like coughing up another grand for the 3.0 and losing a bit more on fuel. It corners flatter and grippier than my E46 and it's great fun. I can imagine having the same fun with a 4 pot any day.