Gil – I am a long time BMW owner, but I am new to the BMW Z-4. We recently moved to Venice FL and I acquired a local 2004 Z-4 2.5i with 73,000 miles. The car is in excellent condition, but I don’t really know much about certain maintenance items for this car. For example, is this one of the BMWs where the plastic water pump impellers implode? And what is the story with the DISA valve – should that be replaced with an updated metal version to avoid issues? Other than some autocross, I don’t plan on tracking this car. Please let me know what you think I should do if anything in terms of maintenance or preventative care now. Many thanks in advance Gil.
Hello Mr. Rausser, sorry for the delay, we have been very busy at the shop. Let me address you questions, first, the water pump was originally the one with the plastic impeller, most of them have been replaced by now, and hopefully replaced with the metal impeller upgraded pump, however, there is no way to know unless you remove the pump. If you are going to do that I would recommend replacing the pump and thermostat.
As far as the DISA valve is concerned I have never had an issue with them breaking but rather the seal leaking. The breaking issue usually stems from build-up in the intake manifold, which causes a build-up in the valve which in turn seizes the shaft and breaks it as the valve tries to move. My recommendation here is to remove the DISA valve, it’s fairly easy. To remove it you will need a T30 Torx, I recommend a 3/8 drive socket as there is limited space, remove the 2 screws that hold the valve to the manifold and remove the valve. Inspect the valve for build up as well as the inside of the intake manifold, if you do see a lot of build-ups I would clean it. There are 2 ways to achieve that, first it is the walnut blasting method, while that is the easiest in a way in that the manifold does not have to come out of the vehicle, I’m going to assume that you do not have the blasting equipment to do it. The second method is to remove the manifold and clean it, the best way is to have it ultrasonic cleaned. There are machine shops that have the equipment and the intake will come out good as new.
Another point on the build-up, the best way to prevent the issue is to prevent the build-up to form in the first place. To do that use only 93 octane fuel, periodically every 3000 miles or so add a good fuel system cleaner in the fuel, such as Chevron Techron as lastly regular oil changes, you should be using synthetic oil and changing fit every 5000 miles or 6 months, whichever occur first.
Another common item is the oil separator, it does contribute to the intake build-up when they fail as well as running issues. If you do not know if it has been replaced recently I would consider it as a preventative item. The front lower control arm bushings are a common failure, you can have them checked. They are relatively inexpensive. Aside from the items listed above, you will be looking at all of the common items such as spark plugs, filters, hoses, etc.
Please let me know if you have any other questions and enjoy the car. Thank you.