Workshops sometimes experience a strange humming noise generated from the area of the fuel filter element when replacing the MAHLE Original KL82 filter. This is usually due to excessive air in the system; the fuel pressure regulator, which is integrated in the housing, becomes noticeable acoustically, particularly with the KL82.
In order to prevent the air from penetrating, the following should be observed when replacing the filter:
1. Before you start removing the filter, remember to wear the appropriate protective clothing (safety goggles, gloves, etc.) when working on the fuel system.
2. In order to reduce any residual pressure in the tank, briefly open the tank cap.
3. Before removing the lines, shut all connections on the line filter using suitable tools. This prevents fuel from escaping and the lines from emptying and, thus, additional air from penetrating the fuel lines.
4. During installation, pay close attention to the flow direction (pictured below) printed on the filter. Don’t interchange the fuel lines and always replace damaged hoses and clamps.
5. After the filter replacement, check all connections and fittings for leaks and tightness.
If disturbing noises persist, despite following the correct filter replacement procedure, this can also be due to a defect in the fuel delivery. To locate the fault, MAHLE Aftermarket recommends that you check the fuel pump, the tank ventilation, and the pre-filter.
Oil pressure problems
After replacing the MAHLE Original OX339/2D oil filter, it’s possible that the oil pressure indicator lights up, despite an oil pressure check not showing any significant problems. Often the oil filter is suspected as the cause of the problem. Due to an increase in enquiries about this phenomenon, the specialists at MAHLE have carried out various tests and identified the source of the fault.
Return valve – not leak-proof?
The majority of oil filter housings used in OE and the aftermarket have an integrated, spring-loaded oil return valve. Unscrewing the filter insert releases the valve, allowing the oil in the housing to flow into the oil sump. This ensures that the complete volume of oil can be drained during the oil change.
The purpose of the valve is to open the oil return channel when the filter is removed, and to close this channel when the filter is fitted. However, experience shows that the sealing ring in the valve can become brittle, with the result that the valve jams and is unable to properly seal the oil pressure channel or the oil return channel, thereby preventing the build-up of adequate oil pressure.
Because oil pressure is usually measured on the section between the oil pump and the oil filter housing, where no significant deviation can be identified due to the design, the fault is usually not noticed at this measuring point.
Check the valve
In order to prevent serious engine damage caused by insufficient oil pressure, MAHLE recommends that you check the valve’s freedom of movement before each oil filter change. The simplest way is to do so by hand, by directly actuating the valve or by briefly pressing the oil filter insert to be fitted into the housing. If the valve jams, or doesn’t move freely to the upper stop, the oil filter housing should be replaced. The housing should also be replaced when the oil pressure indicator lights up after an oil change and there is no other plausible reason for it to be activated.
