Low Coolant Alarm - False reading?

[Ranga]

I have an EMS2 unit in my Defender.

After copping a leaking heater matrix today (which I've temporarily bypassed), and refilling the coolant, my low coolant sensor is now triggering. This is despite the level in the expansion tank being maybe 10mm higher than it should be.

I tried removing the radiator plug (where the sensor also is), and filling it there, being sure to remove the expansion tank plug to allow pressure to release.

I thought it might be a problem with the hose and splitter coming from the expansion tank being blocked. In trying to remove it to inspect, I snapped one of the barbs off the splitter, forcing me to replace it, so that can't be the problem. :mad:

Ultimately, I'm fairly sure the coolant isn't low, so can understand why the alarm is triggering.

[Brett1066]

Check you don't have an airlock somwehere in the system - I had a similar thing happen with my sensor when the radiator was re-filled. Even though there was plenty of coolant the alarm kept going off. Eventually I was able to bleed some air out of the system and all has been good since.

[Ranga]

Check you don't have an airlock somwehere in the system

Yeh, that's what I suspect. What's the best procedure for removing an airlock?

[Brett1066]

I undid the plug on top of the thermostat and gave the radiator hoses a squeeze a few times, then put the plug back and ran the engine for a bit. Im sure someone else will have a better way. The 300 tdi seems to be ok at sorting itself out with airlocks given time

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[86mud]

Ranga, try parking up a hill with front of car facing upwards.

Undo bung on thermostat housing and let car idle for a bit, then replace bung, then top up coolant via the expansion tank.

There is a bleed valve on the small hose from the top of the radiator to the overflow tank. They can stick.

I know with mine if I ever play with the cooling system, it takes a little bit of time for the coolant alarm to settle down again.

There are several threads around on bleeding a 300TDI cooling system.