Replace D4 Coolant Expansion Tank and Sensor


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Coolant sensors can fail and should be replaced with the tank : credit: © Dave Barker
Dave Barker explains the details of this simple, but critical, Discovery 4 DIY job

Need to know

Time: 1½ hours.
Cost: See below.
Difficulty: 1 out of 5.
Models: Discovery 4.
Tools needed: General workshop tools, hose clamp and hose clip pliers.
Parts and costs: Coolant expansion tank with sensor (tank radiator overflow) for Discovery 4 (and Discovery 3), part number LR020367 at Britpart, from £28 to £103 for a Genuine Land Rover part.
Work safely: Allow time for the engine and the coolant to cool before working on the coolant system. When removing the expansion tank cap, take care as the system could still be pressurised and a scalding injury could be caused by steam or hot coolant.
• Use appropriate masks and eye protection when required.
• Use a suitable container to collect any coolant that will be lost and always dispose of the coolant in a manner that protects the environment.
• Always wear protective gloves or barrier cream to protect the hands and skin from fluids, oils and sharp edges of components.
Thanks to: Maddison 4x4, Water House Farm, Station Road, Topcliffe near Thirsk, YO7 3SG.
01845 587407.

Most later Land Rovers use a sensor probe in the coolant expansion tank to monitor the coolant level, giving a visual warning on the instrument display if the level becomes low. Like all electrical components, the sensor can fail, resulting in warning messages and warning lights being displayed even when there is adequate coolant in the system or, worse, showing a misleading correct level when the coolant is dangerously low. In the case of this 2010 Discovery 4 with 195,000 miles on the clock, it was the coolant level sensor probe that had failed and was giving a false reading, suggesting the coolant level was low when, in fact, it was at the correct level.

To fix this problem, the sensor needed to be replaced. The level sensor probe is a push fit into the bottom of the expansion tank, and can be easily replaced once the expansion tank has been removed from the vehicle. However, an aftermarket expansion tank, complete with a pre-fitted sensor, can be found for less than the cost of just the sensor. Because the expansion tank needs to be removed to fit a new sensor, the labour costs are much the same. Another problem that often happens with the expansion tank, which is a common part on Discovery 3, 4 and early Range Rover Sport, is that, as they age with the vehicle, they’re known to split, and the coolant hose outlet pipes can fracture at the tank, causing coolant to leak. So, complete replacement is more cost-effective because the new expansion tank and sensor will be good for another ten-plus years of service.

Replacing the expansion tank is not a difficult job. The trickiest part is disconnecting the expansion hose at the bottom of the tank, it being fiddly to clamp the hose off and disconnect the hose clip. Before starting this job, it is essential to allow the engine and all of the coolant system to fully cool and, even then, to exercise caution when disconnecting or opening any part of the system.


Removing the tank

Location of the tank: The coolant expansion tank is located in the front left-hand corner of the Discovery between the auxiliary pre-heater, power steering tank and the headlamp unit.

Unclip grille: The left headlamp (viewed from driver’s seat) needs removing. First we pull the grille from the front panel after releasing the four clips along its top edge.

Release and lift: To remove the headlamp, we pull up both black locking clips on top, then lift the lamp out from its lower locating pins and disconnect the rear multiplug.

Remove washer tube: We now see the expansion tank. The windscreen washer tank’s black filler tube in front is unclipped and, with filter, pulled from its tank behind the bumper.

Slide up: Adjacent power steering fluid reservoir tank needs to be slid upwards and removed from its mounting on the side of the coolant expansion tank, and placed aside.

Long-reach extension: The coolant expansion tank is secured to the inner wing by two bolts located at the base of the tank. Use a long extension to reach the bolts.

Bolts out: Once the two bolts have been removed, the expansion tank is now loose and
can be moved to give better access to remove the coolant hoses, the next step.

Unclip and detach: Using hose-clip pliers, the coolant vent hose on the top outlet of the expansion tank is released and then pulled off, collecting any escaping coolant.

Clamp it: A suitable hose clamp is fitted to the lower hose to stop coolant loss, before releasing the clip and pulling the hose off from the bottom outlet pipe.

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Lift and unplug: The tank is lifted to release its locating pin from the body panel. It is then manoeuvred in order to disconnect the sensor multiplug located on the bottom.

Lifting out: The expansion tank is now free, and can be lifted out from the Discovery. The filler cap is removed because it will be fitted to the new tank.

The concern: Here is the sensor which failed, on the bottom of the old tank. After the work involved so far, it’s sensible to renew both the tank and sensor.


Installing the new tank

New part: The new tank, part no LR020367 from Britpart, is supplied with the sensor already fitted. There’s nothing like a clean tank for making easy visual level checks.

Twisting: With a little bit of manoeuvring, the new coolant expansion tank is located into position; some people find fitting it into position through the headlamp space easier.

Reconnecting: The multiplug is clipped to the new sensor, and the tank locating pin correctly located before pushing the tank down into its normal, seated position.

Tightened down: After refitting the bottom hose and clip, the hose clamp is removed and the tank secured with the two mounting bolts, which are tightened to 10Nm.

Fully assembled: After all parts have been reconnected and refitted in the reverse order of removal, the system is filled with the correct proportion of water and specified antifreeze.

Is it full?To check the level is correct, it is viewed from the side and should be between the two level marks – a light behind the tank helps visibility.

Let the air escape: The engine is started, and any air in the system is carefully removed through the bleed valve in the top of the tank (being aware of hot coolant).

After reaching full temperature, the engine is switched off and the level re-checked, and a close inspection for leakage is made around the reconnected hoses. The engine and coolant must be allowed to fully cool before attending to any leaks. If all is well, it’s advisable to frequently monitor the coolant system in this way for the first few miles.


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