Water temp of the chart!!!!

[Birty]

Plz help, my temp warnin light flashes as per useal on pre ignition then goes off but then even before iv started the engine the needle goes off the guage & the warning light starts to flash & wont go off !! Does this sound like a electrical fault (maybe a short ) or is this somthing more major ? Im driving a 1.9petrol, it does seem to be drinking water lately?? anybody had the same prob? as always no pre- warning of this prob,one day it was fine the nxt its not !! plz help.. thanx all, sime.

[AngeloEvs]

If the temp gauge is swinging to the right with just the ignition on then you have an electrical fault. Assuming that this has started for no apparant reason I would check the following: If the fault clears after carrying out one of the tests below then you need to investigate possible problems.

1. Remove the module 43 or sometimes marked 42 (usually fitted in the fuse box or above it and looks like a relay) then test gauge with ignition on. If fault clears replace module 43.

2. Inspect/disconnect the connections at the temperature coolant sender in the thermostat housing and then switch the ignition on. On post 86 vans there are two senders in a plastic thermostat housing - the coolant temperature sender is the one facing the cab and colour code of wire is yellow/red. If fault clears then possible problems include short circuit across sender connection, the sender is short circuit, or yellow/red wire short circuit en route to sender.

3. Disconnect the multi-connector on the rear or underside of the dashboard and refit it. This may be a vertical type on rear of dash or a horizontal type under the dash pod.

[Birty]

Cheers il try that & let u know

[ghost123uk]

even before iv started the engine the needle goes off the gauge & the warning light starts to flash & wont go off !! ?

[and]

I'm driving a 1.9 petrol, it does seem to be drinking water lately?? .

Those are 2 separate faults.

Follow Angelo's advice (he is our resident expert on this subject (and others) for the gauge problem.

However, the "drinking water" thing needs to looked at sooner rather than later ! These engines do not react well to low water or the accompanying airlocks. Look for any leaks, often obvious due to having a whitish deposit in the immediate area (dried up antifreeze). Check your expansion bottle (the one on the left), is it full to the top ?

[Birty]

Right , 1st thanks for all advice, ive now think iv found the prob, top tank was low on coolent so filled up to brim, this solved the temp warnings but on parking up after a short trip i noticed the old girl has become incontent! now all i gota do is find the leek!!! Well looking on the bright side at least i know my warning lights work , il let u know how it goes, fanx again, sime.

[ghost123uk]

even before iv started the engine the needle goes off the gauge & the warning light starts to flash

Angelo, in view of the OP saying his water level sensor was out of the coolant (low coolant) and this behaviour has stopped now it is topped up, what do you make of the needle going over to the right before the engine has even been started ?

I ask because I seem to recall some conversation about the "system" moving the needle over so the driver can clearly see the LED (under normal driving conditions). Someone said that this feature is non existent on any variation, but do we see it here ?

[Evsi]

Mine does it too. Needle goes all the way to the top with ignition on and then goes back to normal when started.

[AngeloEvs]

Not sure about that behaviour, I assumed that the engine was cold. Maybe the engine had been running prior to OP switching on the ignition and had got to overheat situation - that was not mentioned. You know your self that if you disconnect the plug at the level sender the only effect it will have is to start the LED flashing sequence after a short delay.

However, the pulses emitted from the Module 43 (which trigger the LED) could fool the gauge into thinking the temp is higher than normal but I wouldn't expect to see this happening immediately - the pulses emitted are every second or so.

The pulses from Module 43 are negative, these negative pulses are fed into the output of the gauge which would be a steady voltage determined by the resistance of the temp sender. As the engine overheats, this steady voltage at the gauge output starts to fall as the resistance of the sender falls due to heat. Injecting negative pulses to a positive voltage does exactly what you learned in maths at school +7 and -3 = 4. You can see how the system works:-

1. Engine temp is fine output terminal of gauge is 8V

2. Engine overheats, sender resistance drops and output terminal of gauge drops to 5v gauge swing right and LED flashes.

3. Engine Normal and output voltage is +8v but coolant is suddenly lost. Along come the negative pulses at around -5v the voltage on the output is now ....... (+8 and -5) = +3. The LED circuit in the gauge thinks the sender resistance is much lower than it really is.

The reason that VW used low frequency negative pulses was to prevent them interfering with the true temp reading but, if module 43 transmits these pulses at a higher frequency or the negative value is higher than normal I suppose we could see the temperature gauge deviate even though it shouldn't unless the loss of coolant condition was ignored.