z4-ext-008BMW’s Z3 was never really the success it could have been but the car that followed it, the Z4, was a much-improved product, although the Z4 was never really a direct replacement for the Z3.

The earlier car had launched with a 1.9-litre four-cylinder engine as a means of breaking into the lower-cost end of the roadster market.

But the Z4 used only six-cylinder engines and, unlike the Z3, didn’t rely solely on a roadster version to make its impact.

In fact, the Z4 coupe was, for some people, an even better bet and sold well alongside its drop-top brother. Unfortunately it wasn’t available until 2006.

In any case, the convertible version merely adds another level of intrigue to what looks like, and in fact is, a serious piece of hardware.

If the main criticism of the Z3 was that it needed to harden up, you wouldn’t say that of the Z4.

From 2003 the Z4 Roadster is available as a 3.0i (3.0 L I6 with 231 hp), a 3.0si available with the new generation 3.0 L I6 with 265 hp (198 kW), a 2.5si with a 2.5 I6 with 218 bhp (163 kW; 221 PS), a 2.2i with a straight-6 170 bhp (127 kW; 172 PS) engine, or a 2.0i with a 150 bhp (112 kW; 152 PS) 2.0 L I4. The Z4 coupé is available only in the high-performance 3.0si trim powered by the 3.0 L 255 hp (190 kW) I6.

A five-speed automatic was available on either version (and it was popular) but for a purer driving experience, the wise move was to opt for the manual gearbox.

The 2.5-litre car had a five-speed unit while the 3.0-litre had a six-speed manual.

Either manual can feel a bit springy at first but most get used to it quickly and then discover it’s quite an accurate shift.

Equally – if not more – impressive is that inline six-cylinder engine.

The 2.5-litre is sweet and smooth and so is the 3.0-litre.

It’s simply that the bigger motor has an extra 30-hp of shove and that equates to a very brisk car indeed.

A straight-six BMW engine is worth the price of admission alone purely for the sound it makes and the wonderful flexible nature is displays.

Drive either of these variable-valve-timing engines and you’ll be wondering why the world is rushing to embrace the V6 over the inline. It comes down to packaging.

Though pitched against the likes of the Porsche Boxster, the BMW roadster offers a more relaxed, less hardcore experience.

Ride quality is very good, yet body roll is well controlled and the steering is sharp and direct. It’s only when speeds reach race-track levels that the Porsche will assert itself through a tauter chassis and only a slight tendency towards over-steer with the slightly softer rear set-up of the Z4.

A large contributing factor to this agility is the Z4’s reasonably low weight which, sits between 3,200-3,500-lbs depending on your transmission choice.

Interior-wise, the Z4 followed the BMW trend at the time of keeping the layout neat and tidy and incorporating a brushed alloy-look band that ran the width of the dashboard.

Safety was good with even the 2.5-litre version fitted with front and side airbags, anti-lock brakes, stability control and traction control.

A major part of the Z4’s attraction for most people is its appearance, so it’s worth making sure that it hasn’t been bashed around too much by a previous owner.

On cars with optional body-kits, the front spoiler can be very vulnerable to curbs and driveways. A good smack will actually break the spoiler but even a minor scrape can leave it looking rough.

While we’re on the subject of options, some sellers will try to recoup the cost of factory options almost dollar for dollar with what they cost new. While factory add-ons do add some value, it’s not as much as some sellers would hope. Make sure you don’t pay full freight for somebody else’s idea of good taste.

Those big alloy wheels that look so good in the brochure are also a real magnet for concrete curb rash. Scuffed and scraped rims are a very real possibility and they’re neither cheap nor simple to fix once they’ve been scraped.

It’s worth taking a close look at the roof on soft-top versions, too. Plenty of these have been sliced open by thieves to help themselves to anything sitting on the seats but at least this sort of damage is easy to spot. Less obvious but just as important is a soft-top that leaks every time it’s parked in the rain. This is hardly common on the Z4 but rubber seals on any car can deteriorate with age, allowing rainwater in. Check that the carpets are dry and have a good sniff when you first put your head inside the car. A musty smell is a pretty good sign there’s a leak somewhere.

Inside, check that the power windows go all the way up and down smoothly, quickly and with no noises apart from a muted whirr from the electric motor. A window that’s slow or stops halfway is probably caused by the window regulator and these can be pricey to replace.

The windshield wipers can sometimes lose the ability to operate intermittently, so check that, too.

On the mechanical front, modern BMWs have a sophisticated system of deciding when the vehicle needs a service.

Rather than simply rely on a set time or distance, the Z4’s computer looks at how many miles it’s traveled over what time and then factors in things like how hard and how fast it’s been driven over that time and distance.

Use a BMW sparingly and sympathetically and the service intervals can be as long as 30,000 Miles. Use all the performance all of the time and the computer will shorten the distance between servicing.

Either way, it’s important to make sure the car you’re looking at has an up-to-date service record.

The correct grade and type of coolant is critical in these engines, too, and tap water can have a disastrous effect on the alloy engine components.

Some Z4 owners reported higher-than-expected tire wear, mainly on the rear wheels. A quick check will soon tell you whether the rear tires are worn more than the fronts and whether the wear is even across the tread.

If it’s not, there could be some wheel alignment or suspension issues. ..or maybe a few burnouts in its recent history.

Speaking of wheels, these do not come with a spare tire from the factory, so it’s a good idea to have a contingency plan in that situation. Either a small pump and some sealer, run-flat tires, or a space saver spare tire.

Aside from anything else, a relatively new, expensive car like this without a stamped service book poses more questions than it answers. As with most cars, the older they get, the more electrical problems they will have, but these are pretty solid cars and the engines are near bullet proof. As long as all the proper maintenance has been done over the years and have had no accidents you should feel pretty comfortable buying the car.