If you need a water pump for your newer diesel you’ll need to decide what type of water pump to buy – swtichable or non-switchable. We’ll review the pros and cons of both water pump options.
What does Switchable Water Pump Mean?
A so-called switchable pump is a water pump design which can change the amount of coolant that it pumps via some sort of mechanical funciton.
Why do Switchable Water Pumps Exist?
Since water pumps are locked to spin at the same rate as the engine the pump cannot vary its pumping volume due to any factors other than RPMs. This means that the water pump will pump the same amount of coolant regardless of engine temperature – hot or cold, the water pump does the same amount of work.
This is obviously not ideal as pumping coolant will slow the engine from reaching operating temperature. A engine that is running under operating temperature will be less efficient and have increase emissions. As government regulators began enforcing stricter emissions regulations an emphasis was placed on getting engines to reach operating temperature as fast as possible.
How do Switchable Water Pumps Work?
Switchable water pumps come in many forms, but the most common type involves a mechanism that moves to prevent the water pump impeller from pumping coolant. This typically comes in the form of some sort of shield or shroud that will extend over the pump, preventing coolant from being circulated. When more coolant flow is required the shield will retract. Conversely when coolant flow needs to be limted the shield will extend to cover the impeller. Some water pump designs will move the pump impeller instead with the impeller moving in and out depending on the coolant flow designated.
What Makes Switchable Water Pumps Move?
The switchable water pump mechanism can be operated by engine vaccuum or by hydraulic pressure. Vacuum operated pumps will be connected to the engine’s vacuum system, with the vacuum going to to the water pump impeller or shield being modulated by a vacuum solenoid valve. A pump that uses hydraulic pressure will use an electronically operated valve to direct coolant to different parts of the pump which will then cause pressure to move the shield.
Did TDIs come with a switchable water pump from the factory?
Model year 2015 TDIs with the EA288 engine code used a switchable water pump from the factory.
Can I use a Non-Switchable Pump in my EA288 2015 TDI?
In our testing a non-switchable pump can be used in a 2015 TDI without any issues. A non-switchable pump will have the same maximum performance as a switchable design, to over-heating is never a concern.
EA288 Non-Switchable Water Pump
Did Mercedes Sprinter Vans use Switchable Water Pumps?
Sprinter vans that use the the OM651 2.0L 4-Cylinder engine use a vacuum operated switchable pump. The switchable design has been the cause of problems, however. In these engines the water pump switching mechanism can fail and allow coolant to enter the vacuum system. This can lead to drivability problems. Check out our article on this problem – Sprinter 4-Cylinder OM651 Losing Coolant, Limp Home Mode – READ THIS!
Can I use a Non-Switchable Pump in my Sprinter Van?
Mechanically there is no problem using a non-switchable pump. However, the engine programming can sense that engine warm up time is delayed and can set a check-engine light for a thermostat or water pump warning. Unless the ECU is reprogrammed there may be a light in the van’s cluster and it may cause the van to fail inspection. Therefore, installing a non-switchable pump in a Sprinter Van is not recommended.
Do Mercedes GLK, ML, GLE or E-Class Bluetec use Switchable Water Pumps?
Yes, all OM651 4-cylinder Bluetec models use a switchable pump, including the GLK250, E250, ML250 and GLE300d models.
Can I use a Non-Switchable Pump in my GLK, ML, GLE or E-Class Bluetec?
Mechanically there is no problem using a non-switchable pump. However, the engine programming can sense that engine warm up time is delayed and can set a check-engine light for a thermostat or water pump warning. Unless the ECU is reprogrammed there may be a light in the car’s cluster and it may cause the van to fail inspection. Therefore, installing a non-switchable pump in a Mercedes vehicle is not recommended.
