Thread: Radiator Overflow Bottle - how does the low level sensor work? Coolant Level Low Warn

Originally Posted by Tombie

Define a great life.

How about I just define not a great life - failure at 180,000km/8 years. Comparatively my 18 year old D2a Td5 unit is still going at 305,000km...

Similar situation with all four door lock actuators on our D4 having been replaced due to non-functioning failure before 7 years/170,000kmn while the D2a is still on originals... Our D1 is still on originals at 23 years old too...

The D1 and D2 components have lasted a great life, longer than I could reasonably expect. The D4 components have not - in my opinion they've failed early - perhaps they build the D4 out of pattern Britpart parts from the start?

On a side but somewhat related note, the coolant overflow bottle on my old Mazda is the original unit still - that's 32 years / 194,000km old now...

Anything in a hot environment, like an engine bay, that is made from plastic or rubber that lasts more than 10 years has done very well in my opinion.

My original bottle lasted 11 years and I only replaced because it was the float that stopped floating.

It was about the same age that plastic and rubber bits in the engine bay on the D2 started to fail.

I will start to look for plastic and rubber bits to change out proactively on the D3 as feel I am on borrowed time.

Interestingly I flushed the cooling system on our second MY12 D4 TDV6 yesterday. Filled it up with water and Penrite cooling system cleaner and the Coolant Level Low warning started coming up on this vehicle too.

Either it's bad luck and both have failed within a few days of each other.

Or, I was reminded of having previously read kenl's comment in this thread at D4 Coolant Level Sensor

Originally Posted by kenl

I was getting the low coolant level after changing/flushing my coolant, the messages were every time i drove the car despite the levels being correct.

There is a video (on the net) showing that the float will sink in water or float in coolant, suggesting that the float is in fact a hydrometer as well as a level warning.

Anyhow, when refilling mine after many flush cycles I only put in 5 liters of coolant concentrate then about 3 liters of water, that was it, even after bleeding it was full.

With a system capacity of 11.8 liters I needed 5.9 liters of coolant concentrate to get the correct mixture. By sucking out 1 liter and replacing it with concentrate the low coolant warnings are gone, for last week at least. If you were refilling with premix you would have no hope as the system does not fully drain, at least not when draining as per the workshop manual.

Perhaps he's right about the hydrometer aspect of it, or it's a cause of when the systems are being drained/cleaned the floats are failing - maybe they don't like being disturbed after 7 years or so of sitting in almost the same place the whole time...

Originally Posted by twr7cx

Interestingly I flushed the cooling system on our second MY12 D4 TDV6 yesterday. Filled it up with water and Penrite cooling system cleaner and the Coolant Level Low warning started coming up on this vehicle too.

Either it's bad luck and both have failed within a few days of each other.

Or, I was reminded of having previously read kenl's comment in this thread at D4 Coolant Level Sensor



Perhaps he's right about the hydrometer aspect of it, or it's a cause of when the systems are being drained/cleaned the floats are failing - maybe they don't like being disturbed after 7 years or so of sitting in almost the same place the whole time...

I had same problem when draining and flushing coolant that the low coolant light stuck on in a 12 year old bottle. On refilling the new coolant I gave the bottle a few sharp taps and it’s been good ever since. Since the float sits in a top range all its life maybe the bottom of the range is a bit slimy sticking the float, maybe the float swells and jams or maybe a combination of the two issues with different SG of water. It seems a common fail at coolant change time.

Originally Posted by twr7cx

How about I just define not a great life - failure at 180,000km/8 years. Comparatively my 18 year old D2a Td5 unit is still going at 305,000km...

Similar situation with all four door lock actuators on our D4 having been replaced due to non-functioning failure before 7 years/170,000kmn while the D2a is still on originals... Our D1 is still on originals at 23 years old too...

The D1 and D2 components have lasted a great life, longer than I could reasonably expect. The D4 components have not - in my opinion they've failed early - perhaps they build the D4 out of pattern Britpart parts from the start?

On a side but somewhat related note, the coolant overflow bottle on my old Mazda is the original unit still - that's 32 years / 194,000km old now...

How about we define it by cycles?
How many stop start cycles?
How many door actuations?

How about working environment?

It’s never that simple.

My D1 required door actuators at 3 years
Coolant bottle at 5 years.

D2 required a window regulator at 11 years and nothing else. Although coolant bottle looks questionable.

D4 at 9 years is going strong on all fronts.


Have you had all of those vehicles from new? Can you be certain they haven’t been treated differently? Think about it, dirt, grit, washing habits, chemicals used... frequency.

Local environment etc all have a part to play in how a vehicle ages.

Including things like:
People pulling handles before the doors unlocked and the button is pressed.
Transmissions - reversing and then shifting to drive without coming to a complete stop (very very common) and reduces life

Way too many factors...

Your D2 came from a former member IIRC and had quite a bit done prior to your purchase.

My personal experience with this problem was that the low coolant warning would come on when the engine coolant was warm, coolant was always at the correct level & concentrate of corrosion inhibitor correct.
It appeared that the float sank when hot, and I've been informed by people more knowledgeable than I that after a period of time the float will absorb coolant and become a non float when hot.

Replacing the whole tank is the go, as a supposed reliable workshop replaced the sensor & the fault remained.

I fitted an 'AFTERMARKET' Expansion tank and then a problem appeared. I would detect the aroma of coolant as I was driving and when checking under the bonnet I could see a fine spray of coolant. This only occurred about two hours after driving with the caravan attached. I could drive all day unloaded in the hottest ambient temperature and it would be ok. Suggestions were that had had a head gasket starting to go and was on the verge of a very expensive engine replacement.

MR Auto Automotive at Redcliffe QLD (Thank You) made a suggestion to replace the tank with a genuine or Meyle replacement, which I did. That was around 30k ago and no problems since. It seems the more economical aftermarket items have a different expansion rate of the plastic between the cap & the bottle & at operating temperatures the cap is allowed to release just enough to reduce pressurising and allow a small spray of coolant under pressure to discharge.

As suggested previously, fit a Genuine or Quality aftermarket expansion tank.

Cheers, Wayne

Originally Posted by Journeytower

My personal experience with this problem was that the low coolant warning would come on when the engine coolant was warm, coolant was always at the correct level & concentrate of corrosion inhibitor correct.
It appeared that the float sank when hot, and I've been informed by people more knowledgeable than I that after a period of time the float will absorb coolant and become a non float when hot.

Replacing the whole tank is the go, as a supposed reliable workshop replaced the sensor & the fault remained.

I fitted an 'AFTERMARKET' Expansion tank and then a problem appeared. I would detect the aroma of coolant as I was driving and when checking under the bonnet I could see a fine spray of coolant. This only occurred about two hours after driving with the caravan attached. I could drive all day unloaded in the hottest ambient temperature and it would be ok. Suggestions were that had had a head gasket starting to go and was on the verge of a very expensive engine replacement.

MR Auto Automotive at Redcliffe QLD (Thank You) made a suggestion to replace the tank with a genuine or Meyle replacement, which I did. That was around 30k ago and no problems since. It seems the more economical aftermarket items have a different expansion rate of the plastic between the cap & the bottle & at operating temperatures the cap is allowed to release just enough to reduce pressurising and allow a small spray of coolant under pressure to discharge.

As suggested previously, fit a Genuine or Quality aftermarket expansion tank.

Cheers, Wayne

Mine went after a coolant change. Not straight away.. But not more then a year. Fitted genuine. Checked it all good. The other problem with crap tanks is when the pressure doesn't reach rated 15psi it lowers the boiling point. Someone on here thought they had a major due to coolant coming out. Had the tank and cap changed. All good again. Aftermarket is getting more and more problematic. Wayne is spot on. Yes these cars cost money. Way more then most. But they also out perform more then most and often.

Actually I'm wrong. I first got an aftermarket tank fitted to my car and could smell Coolant but couldn't see it anywhere. Then I seen a similar post and went genuine.

I ended up having to replace mine as the low coolant warning came back again.