Coolant Temp Flashing - Something a little different ....

[MidLifeCrisis]

Anyone like to take a stab at this?

The scenario:
1) Engine off, turn key to first position
2) Coolant needle fully left (cold), light flashing permanently (ie doesn't stop flashing after 10 secs)
3) Start engine; light goes out!!

How is this even possible!
If the coolant level sensor system is faulty - I thought the flashing continued and it couldn't be extinguished except by a recycle of power?
If the coolant temp sensor is faulty - the needle would need to be fully right (hot) to make light flash.

Have checked coolant level in the tank and it is fine - but even if it wasn't I don't think that this would explain the scenario above.

My only straw to clutch - it's some sort of weird earthing thing that can't be explained but might be fixed by cleaning the earths?

Any other ideas?

[Hacksawbob]

https://club8090.co.uk/wiki/Co ... ht_on_dash" onclick="window.open(this.href);return false;
have a read

[MidLifeCrisis]

Thanks - I did have a read through that and there are a number of things in there to have a go at but was just wondering if anyone had a theory as to why starting the engine would extinguish the flashing light.
As far as I can tell, starting the engine is 'resetting' the LSCU (Level Sender Control Unit) (and at the same time, correcting the 'false fault' (coolant level sensor) that caused the flashing in the first place)?
But I can't understand why/how this is possible? Could the higher voltage provided by the alternator vs the battery be some sort of factor.
I suspect its going to be one of those "I cleaned a few of the grounds up and tugged the connector on the dash and it seems to be OK now!" but I'd really like to diagnose it before I randomly cure it?!?!

[mm289]

Hi MidLife,

in my experience, if I read your post right, what your experiencing is the normal operation of the system. It is designed to flash when the ignition is turned on as a self check/visual check that it is working.

Once you start the engine it will go off, or stay on if their is a fault or overheat/low fluid level condition.

If it is on at ignition and off when running then I would say it is working normally.

HTH

MM

[Ian Hulley]

in my experience, if I read your post right, what your experiencing is the normal operation of the system.

You're experience is mistaken it should flash half a dozen times then stop, only flashing when the level of coolant in the header tank drops below the level of the prongs on the sensor, the temperature at the sensor in the t'stat housing exceeds a certain temperature OR the plug comes off the sensor.

The OIL light flashes until the pressure increases as the engine turns over.

Ian

[AdrianC]

in my experience, if I read your post right, what your experiencing is the normal operation of the system.

Ours works very similarly, too. Often it goes off after a few flashes, before you start the engine. However we've got a minor weep from a couple of places, so every now and then the main header tank is low, so the light stays on. Once the pressure in the cooling system pulls coolant through from the catflap tank, and brings the level back to where it should be, the light goes out. If the catflap tank's too low, though, the light stays on.

[MidLifeCrisis]

in my experience, if I read your post right, what your experiencing is the normal operation of the system.

Ours works very similarly, too. Often it goes off after a few flashes, before you start the engine. However we've got a minor weep from a couple of places, so every now and then the main header tank is low, so the light stays on. Once the pressure in the cooling system pulls coolant through from the catflap tank, and brings the level back to where it should be, the light goes out. If the catflap tank's too low, though, the light stays on.

Oh - I thought (from the Wiki and elsewhere) that once the relay thing had been triggered by low coolant that it could only be reset by cycling the power (i.e. turning key fully off, then on again) - the theory being that if the coolant is low then it needs immediate attention (i.e. engine off, get out of seat and do something about it!!)

[Hacksawbob]

could only be reset by cycling the power (i.e. turning key fully off, then on again

yes that is correct, once the light is flashing only ignition off will reset it.

The flashing during ignition on only tests one thing the light on the dash. Its not a relay but a bit of 1980's inteligence in a relay shape box, it generates a AC wave form sends that to the level probe and measures what comes back. The over heat function is handled by this device as well but the info for that comes from the coolant temperature sender of course. The wiiki has the info on how to test which circuit has th issue, low coolant or high temp.

As AngeloEVS is our semi resident LSCU expert do a search on his name to find out loads more LSCU info like this one

https://club8090.co.uk/forum/viewtopic.p ... s#p7744233" onclick="window.open(this.href);return false;

[AdrianC]

could only be reset by cycling the power (i.e. turning key fully off, then on again

yes that is correct, once the light is flashing only ignition off will reset it.

I wonder if this is something that changed over the lifecycle of the van? Ours is '88 - and if it comes on, it'll definitely go off again without having to switch off.

[Hacksawbob]

Try pulling the wires off the level plug on top of the header tank once the engine is started. Light should flash. Replace plug light will remain flashing. That is my experience with 3 different vans all 88-89

[Ian Hulley]

Try pulling the wires off the level plug on top of the header tank once the engine is started. Light should flash. Replace plug light will remain flashing. That is my experience with 3 different vans all 88-89

[keith]

could only be reset by cycling the power (i.e. turning key fully off, then on again

yes that is correct, once the light is flashing only ignition off will reset it.

I wonder if this is something that changed over the lifecycle of the van? Ours is '88 - and if it comes on, it'll definitely go off again without having to switch off.

Mines 89.....and the only way to stop it flashing ....once you have the engine running.....is to turn off and start again.

As Ian say....it flashes half a dozen times at ignition and then should never flash again.

[MidLifeCrisis]

OK - I yanked the module (43) out of the van today to have a play;
I set up this circuit on the bench;



With the switch set as it is in the pic, the light is out (the 27K resistor simulates the coolant probe being dipped in coolant)
- So that is correct operation.

With the switch pushed (i.e. simulate the coolant probe not being in the coolant), light goes ON after about 5 secs
- So that is correct operation too.

Set the switch back to how it is in the pic, and the light goes OUT again (it takes about 30 secs to go out)

So from the experiment it would seem that for my '43 Module' the warning light would be able to go out once it had been set.

Also, I'm surprised how long it took for the light to go out again (i.e 30 secs) ..... I tried a 150K resistor on that switch (in place of the 27K one and it took over 2 minutes to go out! So, if the resistance of coolant is very high (which I assume it is) then its possible that no one has waited long enough to see the light go back on again?!?!

Not sure that any of this answers my original question but its all interesting stuff.

[kevtherev]

if the sensor prongs are covered in crap this can up the resistance.
poor contacts can do the same

[MidLifeCrisis]

Resurrecting this thread to make a note of further odd behaviour with coolant temp gauge and warning light.
Took van for a drive yesterday (so pretty cold outside).
I have the module (43) removed at present - so the coolant level function of the flashing light isnt operating.

Started engine and coolant warning light kept flashing (for 10 minutes) even though the gauge needle was off to the far left (i.e. cold coolant)
How is this even possible? I thought that (without the coolant level circuit working) the light should only flash if the needle was over to the far right (i.e. coolant very hot).
After 10 minutes - just as the coolant needle was starting to rise, the flashing light stopped flashing?
What is going on??