Water level / temp warning light

[3_in_a_bus]

Hi All

Got a odd problem and I am stumped.
When I start the engine from cold everything works correctly no warning lights temp gauge reading correct and all will be fine until I turn her off.
When I restart her again everything is working correctly (inc temp gauge) apart from now the warning led is flashing for over temp / low water.

Engine only need to be run for a minute or so from cold for this to happen but once it cools down all is good again.
If I drive it with the light flashing temp gauge is rises correctly and is stable at around the led (same as if if run her up to temp from cold with no warning light).

I have checked the obvious ie
water lever sensor (was mucky but no change)
Water temp sensor connections + earth's
Earth crowns behind the fuse box
all fuses
Mutipin connector on dash (earth was damaged repaired)
Removed relay thingy no 43
no change still does it

Help, what have I missed
Only started this week (right after she passed her MOT)

[marlinowner]

Is 43 a typo?
"Relay" number is 42.
If light flashes when relay 42 is out, header tank is in the clear.

[3_in_a_bus]

Sorry yes its 42 (was trying to do it from memory rather than checking, makes no difference if in or out

[kevtherev]

There's a lot of information regarding this in the wiki
http://wiki.club8090.co.uk/index.php/Co ... ht_on_dash" onclick="window.open(this.href);return false;

relay 42 and 43 are the same thing

[MidLifeCrisis]

^^^ WHS
But if the problem is still there with the 42/43 relay removed and the needle is reading correctly then that pretty much points to the gauge itself being the culprit (with the only other possibility being that there is a bad earth to the gauge and that is causing weird behaviour),
Try turning the key to the first position but not starting the engine - wait for the light to stop flashing, then turn off, then turn on again - do you get the same incorrect behaviour (ie the led keeps flashing the second time)?

[3_in_a_bus]

^^^ WHS
But if the problem is still there with the 42/43 relay removed and the needle is reading correctly then that pretty much points to the gauge itself being the culprit (with the only other possibility being that there is a bad earth to the gauge and that is causing weird behaviour),
Try turning the key to the first position but not starting the engine - wait for the light to stop flashing, then turn off, then turn on again - do you get the same incorrect behaviour (ie the led keeps flashing the second time)?

If the engine is cold then the diagnostics seem to work and the light goes out (can be repeated as long engine has no heat in it) however if you start the engine even for only a minute or two then then Diagnostics fail.

I did wonder about the gauge as temp reads fine (and stable) which to me rules out temp sensor and wiring. is the control circuit for the warning light within the temp gauge? I did have a spare gauge will try and find it.

Does anyone know if I can wire the 2nd one in without disconnecting the original one (by just taking feeds from the rear) or will this cause an issue?

I have checked the earth and they seem OK ( earth on the multi pin connector for the dash was not as good as it could have been but I have fixed that now and no change).

[MidLifeCrisis]

If the engine is cold then the diagnostics seem to work and the light goes out (can be repeated as long engine has no heat in it) however if you start the engine even for only a minute or two then then Diagnostics fail.

This behaviour doesn't make a whole lot of sense - have you tried disconnecting the wire from the coolant temp sensor and see what the effect of that is?

I did wonder about the gauge as temp reads fine (and stable) which to me rules out temp sensor and wiring. is the control circuit for the warning light within the temp gauge? I did have a spare gauge will try and find it.

The 'control circuit' for the light is within the gauge - in simple terms the light will flash whenever the resistance on the signal/sensor wire reaches a certain level. So in theory the light will only flash when the needle reaches a certain (hot coolant) point ..... however the 42/43 relay gets around this by sending short pulses of 'low resistance' on that signal/sensor wire which are enough for the 'control circuit' to flash the light but not last long enough that the gauge has time to react and move (you'll notice that the gauge needle moves really slowly in response to changes ). So when the coolant level is low, the 42/43 relay will pulse a signal into the gauge to cause the light to flash but the needle will still show the correct coolant temperature (clever eh!!)

Does anyone know if I can wire the 2nd one in without disconnecting the original one (by just taking feeds from the rear) or will this cause an issue?

Not sure - I'd guess that it might cause odd behaviour .... and might end up being more confusing but might be worth a shot if you can't face pulling the other gauge out.

[3_in_a_bus]

Spare gauge is worse than the one fitted led does not even run diagnostics

Looks like I will be keeping an eye on ebay for another gauge.