On The Road

Cooling off a hot problem

A customer with a 2011 BMW X5 recently came in with an overheating problem. Because this car does not come with a temperature gauge, it can be disconcerting when the instrument display tells you that the car is overheating.

The customer said he saw the warning light and also heard the engine auxiliary fan roaring at full speed. This gave me a good idea of what may have happened.

BMWs with N54 or N55 motors (between 2008 and 2014) come equipped with an electric water pump, installed to make the engine more efficient in terms of power, fuel consumption and emissions. They do so by allowing the computer to control the flow of coolant rather than the engine itself. By removing the old mechanical water pump, there is less load on the engine. The old mechanical-style water pump could rob 3-5 horsepower from the engine.

The first thing we did was check the coolant level. Then we connected the car to the Integrated Service Technical Application (ISTA/BMW factory tool). The coolant level was OK.

Next, we checked for codes. Two codes popped up related to the water pump: Digital Motor Electronics (DME) 20A804 (coolant pump switch off due to blockage) and DME 20A701 (coolant pump speed outside of tolerance). The second code, coolant pump speed outside of tolerance, definitely means the water pump should be replaced.

The customer also stated that the engine auxiliary fan sounded extremely loud. This higher auxiliary fan (engine radiator fan) speed is normal. The DME senses that the engine temperature is rising even though the computer is commanding the water pump to move more coolant, and it’s trying to remove heat from the engine with air as a precaution.

Oil-filter housing gasket leaks

One of the reasons I wrote about this is because the electric water pump can just pop up at any time without warning. Once it fails, the car is technically not drivable. One other thing that can accelerate the water-pump failure is if the engine oil-filter housing gasket leaks.

On the N54 and N55 motors, the oil-filter housing sits almost right above the electric water pump. It’s like dripping oil onto your vacuum cleaner – eventually something is going to fail.

We always replace the thermostat with the water pump, because it has been updated on some of the engines and it is next to the water pump. If oil has been leaking from the oil-filter housing gasket, we also replace the gasket and any rubber hose that may have been covered in oil.

If you have one of these cars and the water pump has not been replaced yet – and you have more than 80,000 miles on the car – you should have them checked. Although both repairs are expensive, it’s better to have them checked or replaced before they cause bigger problems.

Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call 960-6988, email This email address is being protected from spambots. You need JavaScript enabled to view it. or visit sunnyvaleforeigncar.com.Cooling off a hot problem

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