low water alarm intermittently going off

[Stropp]

as the title says, i have a low water alarm and it goes off now and again and i cant work out whats wrong, if i rev it it goes away, have bled it numerous times and even resorted to topping up the overflow bottle when it was above the full mark. I even loosened the sensor so coolant was coming out when it was warm to try to see if there was an air bubble but still no result, it doesnt do it all the time just sometimes and it has me stumped.

[MudRunnerTD]

Bugger! Silly question from me time! Is that after market or one of the dash lights I have never taken notice of? Is there an audible alarm also?

Have you bled the cooling system? Cap off, funnel, heater on, fast idle, go have lunch.?

[threedogs]

Parking nose up with inverted Coke bottle cut in half
placed in the radiator will raise your fill point and hopefully purge any air out of system

[Stropp]

Bugger! Silly question from me time! Is that after market or one of the dash lights I have never taken notice of? Is there an audible alarm also?

Have you bled the cooling system? Cap off, funnel, heater on, fast idle, go have lunch.?



yes its one with the light and alarm, when i swapped it over i got the car warm so the coolant had slight pressure and when i removed the plug to insert the probe the coolant started to come out so i didnt think any air got in there but as i said i have undone the probe a couple of times so its loose and started the car to see if air comes out but all i get is coolant so unless it has an intermittent fault its got me buggered.

[janderson]

Mine dose it sometimes to. One prob I found was a cracked cap (yellow) on the overflow bottle. $12 from Nissan. Hasn't done it now for a while, but found that if you take any of the caps of that release the pressure it'll will go of ever now and again for a while.

[Cuppa]

I'm still not sure if it's factory or aftermarket. I have an aftermarket one with alarm & light that I fitted in my DX, the sensor screws into the bleed screw hole. Where is yours mounted?

[my third 256]

there is another sensor on the right hand side down low on the radiator this can cause this problem also
(the main battery side)
36249

[Stropp]

I'm still not sure if it's factory or aftermarket. I have an aftermarket one with alarm & light that I fitted in my DX, the sensor screws into the bleed screw hole. Where is yours mounted?

Yep that's the same as mine

[Cuppa]

Yep that's the same as mine

Hmmm, that would seem to rule out the mounting position then. I haven't experienced the issue you describe.
Clutching at straws .... Is it possible your water pump needs looking at? It's possibly a long shot, but I wonder if there has been any 'corrosion' of the water pump causing cavitation (http://en.wikipedia.org/wiki/Cavitation) .... Potentially an early warning sign of future problems. Have you used water rather than coolant? How long does the warning last for?

I'm sure you've checked electrical connections. Alarm goes off when circuit is broken, so an intermittently poor connection would give you an intermittent alarm.

The sensor is screwed fully in isn't it?

Can't think of anything else.

Cuppa

[Stropp]

Hmmm, that would seem to rule out the mounting position then. I haven't experienced the issue you describe.
Clutching at straws .... Is it possible your water pump needs looking at? It's possibly a long shot, but I wonder if there has been any 'corrosion' of the water pump causing cavitation (http://en.wikipedia.org/wiki/Cavitation) .... Potentially an early warning sign of future problems. Have you used water rather than coolant? How long does the warning last for?

I'm sure you've checked electrical connections. Alarm goes off when circuit is broken, so an intermittently poor connection would give you an intermittent alarm.

The sensor is screwed fully in isn't it?

Can't think of anything else.

Cuppa



Yep can't think of anything else, may have to go through everything again!

[bear3103]

Have you tried pulling the sensor out and cleaning it or maybe the sensor is faulty.???.

[Cuppa]

Have you tried pulling the sensor out and cleaning it or maybe the sensor is faulty.???.

The ’sensor’ is only a machine screw screwed into a plastic sleeve.

Whilst in contact with the coolant it maintains an electrical circuit. If the electrical circuit is broken the alarm goes off. So whilst a dirty ’sensor’ could cause the problem, it would be very unlikely for it to be intermittent. It would also seem not possible for it to be faulty. I would think that a faulty connection/internal break in a wire might be the most likely cause, but the fact that revving the motor stops the alarm sounding points more to the ’sensor’ losing contact with the coolant.

[Stropp]

Yes that's what I thought cuppa but I have loosened that sensor a few times and let the coolant fluid out but never had air come out, also after doing that the alarm does not go off for a few weeks.

[NP99]

What about the earthing system? Is it tight and clean? Just guessing now....

[Stropp]

Yeh checked it and it looks good

[nissannewby]

I'm with cuppa in thinking it could be the water pump. On the machinery I work on I have seen a similar thing where the coolant flow is low give it a rev and all good. This is really kinda grasping at straws as you should see other symptoms if a water pump is on its way.

[threedogs]

On the water pump theory have you grabbed
the water pump to see if any play in the shaft,
any signs of coolant under water pump shaft, or further down if dripping.

[kevin07]

try descaling the probe this causes alarms going off in buses they need to be cleaned regular and a specific coolant to stop this happening

[Stropp]

ok will pull the sensor and check it and look for the other bits with the water pump but ihave never seen any leaks.

[Cuppa]

I wasn’t thinking in terms of leaks. Reason I asked if you had run water rather than coolant was thinking about the possiblity that the impeller (or whatever it has) of the water pump may have become pitted or rough, potentially causing diferent swirl patterns/cavitation ................ but it’s a pretty long shot, & not really the basis for dismantling the pump.

Another thought, & I haven’t looked at any diagrams or the real thing, so it’s only a shot in the dark ....... the sensor screws into the thermostat housing. Is it possible that Stropp might have a ‘sticky thermostat’ causing the problem? .... Anyone? Stropp does the alarm go off after a good run, or only whilst the motor is still warming up?

You could also try putting a longer sensor in to see if this makes the problem go away. If it stops the alarm going off you’ll know it’s not an electrical connection issue.

Cuppa

[Stropp]

hi cuppa it goes off both when it starts sometimes and other times after i have had a run and slow down or idle. It could well have air but i have bled it often and it still does it ?

[threedogs]

@ Cuppa More a pressed steel fan than an impellor, I have an Impellor water pump on my 350 motor. Guys name was John Bennet knew everything about cooling a motor. worth a google
seems like its acting as a cathode or what ever you call them. they are in HWS and outboard motors, designed to dissolve.
But thinking I would clean and replace

[NP99]

@ Cuppa More a pressed steel fan than an impellor, I have an Impellor water pump on my 350 motor. Guys name was John Bennet knew everything about cooling a motor. worth a google
seems like its acting as a cathode or what ever you call them. they are in HWS and outboard motors, designed to dissolve.
But thinking I would clean and replace

sacrificial anode.