Coolant pump and electric pumps
How the coolant pump is designed and driven, how a switchable pump stops circulation with an annular shroud actuated by vacuum or hydraulics, and how electric pumps work and check themselves — with examples from different engines.
The coolant pump drives the coolant through the block and the head, but a warming-up engine does not always need it. Based on the self-study programs, we look at how the pump is driven, how an annular shroud switches it off and how electric pumps are designed and monitored.
Mechanical pump
The coolant pump rotates the impeller, which drives the coolant through the cylinder block and cylinder head. (impeller drives coolant through cylinder block and head)
Drives differ: in one engine the pump is driven by a toothed belt from the balance shaft, with a speed reduction. (drive: toothed belt from balance shaft, reduced (i = 0.59))
In another, by a separate toothed belt from the exhaust camshaft on the flywheel side. (other engine: separate toothed belt from the exhaust camshaft, flywheel side)
The impeller is also made of plastic with fiberglass: the special blade profile allows high speeds almost without cavitation. (plastic flap with glass fiber (PPS GF40): high speed without cavitation)
Switchable pump
To make the engine warm up faster, pumps that can be switched off were developed: an annular shroud slides over the rotating impeller, and the coolant stops circulating. (annular shroud over the impeller → no circulation, engine warms up faster)
In one design, the shroud is moved by a vacuum diaphragm via a rod — when the control unit actuates a valve. (vacuum diaphragm + rod · valve actuated by the control unit)
The pump is switched off until the liquid is between minus fifteen and seventy-five degrees, and then switched on intermittently so that the cold liquid from the block is mixed with the hot one gradually. (off at −15…75 °C · then on intermittently)
In another design, the shroud is moved by the coolant itself: inside is an axial piston pump driven by a swash plate on the impeller. (hydraulic actuation: axial piston pump driven by a swash plate on the impeller)
When energized, the valve closes the return channel, the pressure rises, and the annular piston, compressing the spring, pushes the shroud over the impeller. (valve under current closes return channel → pressure → ring piston compresses spring)
Without current the channel is open, the spring pulls the shroud back, and the pump circulates the coolant — the same happens if the valve fails. (no current — channel open: spring retracts the shroud · valve failure — coolant circulates)
Electric pumps
The electric pump combines a centrifugal pump, an electric motor and electronics in one housing, and its connector has three pins: ground, power supply and the signal from the control unit. (electric pump: pump + motor + electronics · 3 pins: ground, power, PWM)
From the signal's duty cycle, the pump electronics calculate the required speed and monitor the motor current. (PWM duty cycle — required speed · motor current monitoring)
Every ten seconds, the pump pulls the signal wire to ground for half a second — this tells the control unit that the pump is working properly. (every 10 s — signal pulled to ground for 0.5 s: “pump OK”)
When the signal wire is cut, the pump runs at maximum speed. (signal wire break → maximum speed)
After the engine is switched off, the electric pump circulates coolant through the turbocharger and protects it from overheating after high load. (after shutdown - turbocharger coolant run-on after high load)
And while the main pump is off, the auxiliary electric pump pumps the hot fluid from the head to the heater, and the block does not cool down. (main pump off: electric pump - head → heater, block does not cool down)
Engine specifics
- 1.8 l TFSI engine (self-study programme 384): the pump, temperature sensor and thermostat sit in a common thermosetting plastic housing under the intake manifold; belt tension is set by the pump position in the housing, so a damaged pump is replaced together with the housing, and the drive gear screw has a left-hand thread.
- 1.2 and 1.4 l TFSI EA211 engines (program 616): the pump forms a module with the thermostat housing on the cylinder head; when the pump is replaced, its toothed belt is replaced too.
- System with a switchable vacuum-actuated pump (program 497): the switch-on and switch-off points depend not only on temperature but also on torque and engine speed; with the pump switched off, an electric pump drives hot coolant from the head to the heater.
- EA288 diesel engine (program 514): if the electric pump fails, a fault is stored and the Check Engine lamp lights up; if the signal wire breaks, the pump runs at maximum speed, and if the power supply fails, it does not run.
Summary
- The coolant pump rotates the impeller, which drives the coolant through the cylinder block and cylinder head.
- To make the engine warm up faster, pumps that can be switched off were developed: an annular shroud slides over the rotating impeller, and the coolant stops circulating.
- In another design, the shroud is moved by the coolant itself: inside is an axial piston pump driven by a swash plate on the impeller.
- The electric pump combines a centrifugal pump, an electric motor and electronics in one housing, and its connector has three pins: ground, power supply and the signal from the control unit.
- Every ten seconds, the pump pulls the signal wire to ground for half a second — this tells the control unit that the pump is working properly.
- And while the main pump is off, the auxiliary electric pump pumps the hot fluid from the head to the heater, and the block does not cool down.
Next episode: supercharger air cooling.