Vauxhall / Opel Astra TwinTop (2006-2010)

Complex hardtop roof

The three-part folding hardtop roof is one of the most intricate designs used in a convertible car. I think the designer must have been a Transformers fan.

The roof itself is put in motion by hydraulic actuators powered by a hydraulic pump. Additionally, there are four plastic flaps that are part of the cover (aka parcel shelf) behind the rear seat. These flaps are powered by electric motors.

While the hydraulic roof is fairly reliable, a typical problem is stripping plastic gears that operate two of the flaps. Over time, the little gears wear out and the flaps can start getting stuck or refuse to move at all.

Luckily, aftermarket replacement gears are available and you can even get brass gears, which are much stronger. The flap gears are inexpensive (∼£30 for a pair) and relatively easy to replace.

It’s possible to do it yourself. Here’s what’s involved:

Apart from the sticking flaps, your two biggest concerns are hydraulic system issues (mainly leaks) and weather intrusion (fancy name for a leaking roof). Things to check regarding the convertible roof:

• Check for any dampness in the footwells and carpets. Also, check in the boot underneath the spare wheel. It’s best to do it after rainfall.

• Open and close the roof a couple times to make sure that it works.

• Check the condition of the roof seals. Ideally, they should be lubricated regularly – ask the previous owner about it.

• Check if the level of hydraulic fluid is correct. If it isn’t, then the car may have been neglected or there is a leak somewhere. This step is optional because it requires some boot trim to be removed. The pump and the hydraulic fluid reservoir is in the boot behind the rear seats.

• Look for hydraulic fluid leaks – in the boot and around the hydraulic rams.

• Get the car up to 60 mph with the roof closed and listen for excessive wind noise.

• Listen for rattling noises while driving with the roof closed.

• Take the car to a high pressure (touchless) car wash and see if any water gets inside the cabin or the boot.

• Accident-free history is very important for any hardtop convertible. If the car participated in a large crash, the roof may be out of alignment, which can make it a nightmare to waterproof if the chassis of the car isn’t “straight” anymore.

Along with the hydraulic system, there is plenty of electronics to manage the roof on the Astra Twin Top. These cars are getting old and sometimes the roof can be a bit fussy (usually small issues though).

A word of warning: If you’re not into DIY and you’re not willing to understand how the roof mechanism operates, you may pay for servicing more than you need to.

The roof on the Astra is very complex and some small things may at some point require fixing or adjusting. If you can’t diagnose or repair these little things yourself, trying to get the roof sorted out at a car repair shop may be expensive.

A good example is the plastic gears that can fail in the pair of flap mechanisms. You can buy a pair of gears online for £30 and replace them yourself, or you can have a single motor replaced for £300 at the dealership.

Usually, dealerships do not replace individual components such as gears, you may have to buy whole assemblies – the motor and mechanism in this case. If the second flap fails later, that will be another £300…

IDS+ shock absorbers (CDC)

Some Vauxhall cars are equipped with Continuous Damping Control (CDC), which a type of active suspension. As the name implies, it actively changes the damping stiffness of the shock absorbers, depending on the road conditions.

It can improve handling in certain situations, like braking or cornering, and soften the suspension when stiff damping is not needed. From first-hand experience, I can say it works quite well.

The CDC is an optional extra in the Astra Twin Top and it’s a part of the “Interactive Driving System Plus” package. You can recognize a car with the CDC by the IDS+ icon appearing on the dashboard when you turn the ignition on.

The icon should disappear a couple seconds after you turn the engine on. If it stays on, there is a problem and the system isn’t working (the suspension gets set to hard damping).

The system is cleverly designed, but at some point, the shock absorbers will need to be replaced just like in any car.

When the time comes to replace the shock absorbers in your Vauxhall Astra equipped with IDS+, you will be looking at around £350 for a new CDC shock absorber. If you want to replace all four, that will be £1500-2000 if you include the cost of fitting.

Luckily, there are other options. You can have the shock absorbers reconditioned for half the price of a new one. There are companies that specialize in this kind of jobs. Another option is to bin the CDC shock absorbers and fit standard shocks for a fraction of the price.

Once the original shocks are removed, the CDC must be disabled in the car’s computer to get rid of the IDS+ light on the dashboard.

M32 gearbox bearings

Some Vauxhall Astra TwinTop models are fitted with the infamous M32 gearbox. A typical problem with this 6-speed transmission is bearing wear. In particular, the 6th gear bearing.

When this bearing starts wearing out, the gearbox becomes noisy when driving in 6th and 5th gear. If not fixed, this problem leads to total gearbox failure (a hole in the gearbox).

The M32 gearbox is used in so many vehicles and bearing failure is so common in high-mileage vehicles, that I’ve dedicated a full page to the M32 gearboxes.

Follow the link above to learn more about the symptoms of bearing failure, the solution to the problem and how much it costs to fix a dying M32 gearbox.

The M32 gearbox is mated to the 1.6 Turbo (Z16LET), 2.0 Turbo (Z20LER/Z20LER) and 1.9 CDTi (Z19DTH) engines in the Astra Twin Top. Other models have a less problematic 5-speed transmission.

1.6T – cracked 4th piston (Z16LET engines)

There have been cases of cracked pistons in these engines. To make it more interesting, it’s only piston no. 4 that cracks.

Obviously, a failed piston is a pretty big problem and will cost a lot to sort out. It’s not standard maintenance and not something you’d ever expect to happen to your car. I think the piston problem is caused by a combination of factors so let’s review what we know first:

• Most of the piston failures happened in the 192 PS Z16LER engines used in the Corsa VXR. Out of these, the majority were tuned cars. Stock engines can fail too, just less often. The percentage of Z16LER/Z16LET engines that fail isn’t large, so there is no need to panic. Well… You can start stressing out if you’re running over 200 PS with stock fuel injectors… By the way, the Z16LER is the same engine as the Z16LET – the difference lies in the ECU settings. The Z16LER is simply tuned for more power.

• The fuel injectors in these engines are just adequate for around 200 PS. If you ask for any more power, the injectors will max out before reaching the top of the RPM range. A maxed out injector cannot deliver the amount of fuel required and the air-fuel mixture will become leaner as the RPM goes up under full load. Lean mixture = excessive heat = cracked piston.

• The pistons are cast and not very durable, otherwise, they would not crack (duh!). People who tune these engines with stock injectors risk breaking their 4th piston. When it goes, they usually replace all pistons with stronger, aftermarket forged ones. This solves the problem.

• Many of the Corsa VXR buyers were below 25 years old. This age group is inclined to go berserk in a 192 PS VXR.

There must be another factor that makes only the 4th cylinder fail while the others are usually fine. I’ve got some ideas as to why it happens. Here they are (these are just speculations, not facts):

• The 4th fuel injector is the last in the fuel rail, which could make it go lean faster than the other three.

• The 4th cylinder is the one furthest away from the water pump. Perhaps, cooling of this cylinder is not as good.

• The intake manifold may distribute air unevenly and feed the 4th cylinder with a bit more air, leaning out the mixture.

• It could be detonation (knocking). 98 RON fuel is recommended by the manufacturer and this could be the reason.

I think it’s time to construct the case:

A young, excited driver has the engine in his car reprogrammed to deliver more power – as much power as the stock hardware can deliver. On a cold morning, he gets in the car and takes off with the tyres squealing, seconds after turning the engine on.

The stock injectors can’t keep up with the driver so the temperature inside the cylinders suddenly rises to dangerous levels. Because of the engine design, the 4th piston gets hit the hardest. The unlucky 4th piston, which was cold seconds ago, goes through a thermal shock. The sudden change in temperature causes high stress inside the relatively brittle cast aluminium alloy.

This is a perfect scenario for piston failure and indeed the piston goes pop! It may not crack immediately, but repeat this a few times and the piston will be on its way to piston heaven.

I think that a lot is down to the driver and how the car is treated. If you already own a car with the 1.6T, sell it quickly before the piston explodes! Just kidding…

If you are worried and you want the engine to last, you should follow these directions:

• Do not tune these cars at all unless you are going to upgrade the injectors. Even with larger injectors, you are increasing the risk of failure.

• Never drive the car hard until the engine is warmed up. Always let the engine cool down before shutting it down. Don’t drive it hard in the last couple minutes before shutting it down and let the engine idle for 15-30 seconds before turning it off. This is good for the turbocharger too.

• Choose the higher octane fuel available in your country. This decreases the risk of detonation.

If you follow the rules above, you should be fine, in my opinion. However, there will always be a very small risk that the 4th piston will pop. This applies even to unmodified cars as some have failed. These engines are not bad but keep in mind that they should not be abused.

The fuel injectors are small so engine tuning is not advised unless the injectors are uprated. You may get away with stock pistons and a remap but I would not take the risk. You are safer at 180 PS.

If you are going to buy a car with the 1.6 Turbo, look out for the symptoms of piston problems: rough running or misfires, unwanted engine noises, increase engine smoke, lack of power. Also, try to find out if the car was not abused by the previous owner.

1.9 CDTi – swirl flaps (Z19DTH engines)

The 1.9 CDTi was an engine designed by Fiat and General Motors (mostly Fiat). In Fiat cars, this engine is known as the 1.9 Multijet. “Multijet” stands for multiple fuel injections per combustion cycle.

These engines use swirl flaps in the intake manifold in order to improve emissions. There are two types of intake manifolds that were fitted to these engines. Here’s a brief description of the manifolds and how they can fail:

1. Plastic manifold with spot-welded, stainless steel swirl flaps. Failure mode: the main cause of flap failure is increased friction in the flap mechanism from the carbon build-up in the intake manifold. Carbon build-up is a byproduct of the Exhaust Gas Recirculation (EGR). EGR systems are commonly used in modern diesel engines to improve emissions. The metal swirl flaps often keep working without any indication of a problem until the spot welds give up and a flap gets detached. It can then enter the engine causing severe damage. An ingested flap can take out valves, a piston, damage the cylinder walls and even the turbocharger.

2. Aluminium alloy manifold with plastic swirl flaps. Failure mode: the flap bearings can wear out from increased friction when the carbon build-up in the intake manifold becomes severe. Once the bearings are worn, they may develop an air leak, allowing the boost pressure to escape. Also, the flaps can simply get stuck before the bearings wear out. These plastic flaps are the lesser evil as they don’t break off.

The Z19DTH has the safer aluminium manifold with plastic swirl flaps. Stuck or leaking swirl flaps manifest as rough engine running, reduced fuel economy and reduced power. The “Check engine” light may turn on.

To fix the swirl flaps, a new intake manifold is required, which is fairly expensive. Another option is to remove the swirl flaps altogether, which has a minimal impact on the engine running. There are swirl flap removal kits available on the market. Please be aware that removing the swirl flaps will increase emissions and is probably illegal – it depends on the country you live in.

1.9 CDTi – timing belt (Z19DTH engines)

According to the manufacturer, the timing belt in this engine needs to be replaced every 100k miles or 10 years, whichever comes first. In my opinion, this is very optimistic. I recommend getting it replaced not later than 60k miles or every 5 years, whichever comes first.

The water pump must be replaced at the same time as the timing belt, otherwise, it can seize and cause the timing belt to snap. It’s actually the water pump that is the weak point in the timing belt drive and the first part to fail.

Summary of problems & additional information

• The Astra TwinTop convertible is based on the popular Astra H. Therefore, most replacement parts (excluding the roof) are widely available and relatively inexpensive.

• When buying an Astra TwinTop, inspect the hardtop roof thoroughly so that you could enjoy the sun, rather than trying to figure out why it got stuck half-open at the traffic lights.

• IDS+ shock absorbers are expensive to replace when they fail. Luckily, their life expectancy is good.

• The 2.0 Turbo (Z20LEL & Z20LER) is a robust unit with potential for increasing power. The Z20LEL and Z20LER are both the same engine. The 30 PS difference in power output comes just from software. The engine itself is solid. Unfortunately, all turbocharged engines in this hardtop convertible are mated to the M32 gearbox.

• The smaller brother of the Z20LER, the Z16LET, comes with a small risk of 4th piston failure.

• The Z16XEP/Z16XER (1.6L) and Z18XER (1.8L) engines may be a bit boring but they are simple and reliable units. They are also mated to a 5-speed gearbox that doesn’t eat bearings like the 6-speed M32 transmission. No dual mass flywheel with the 5-speed gearbox is another bonus. For highest reliability, these are the engines to choose.

• The Astra TwinTop is a heavy car, so the Z18XER (1.8L) is preferable over the 1.6L engines. The only thing to look out for is camshaft adjuster rattle after a cold start. Read this article about timing belts for an explanation.

• All engines in the Astra TwinTop are fitted with timing belts. As far as the 1.9 CDTi is concerned, I recommend getting the timing belt and water pump replaced not later than 60k miles or every 5 years, whichever comes first. The manufacturer’s recommendation (100k miles) is too optimistic in this case.

• Click here for an article that might help you decide if a modern diesel engine, like the 1.9 CDTI (Z19DTH), is the right choice for you. The engine itself is a good unit and the things that go wrong are usually related to the emissions control equipment. This is typical for most modern diesel engines. Also, be aware that the 1.9 CDTi is mated to the M32 gearbox and has a diesel particulate filter (at least in the UK).

• The Vauxhall / Opel Astra TwinTop is one of the better-looking inexpensive hardtop convertibles from that era. In my opinion, it beats the Ford Focus CC and Peugeot 308 CC hands down.

Petrol engines – specs & performance figures

Diesel engines – specs & performance figures

Petrol engines – technical details

Diesel engines – technical details