Coolant sensor & Temperature

[Jutstar]

I ve got a flashing coolant sensor on my 1989 T25, Leisuredrive, I have had the engine serviced today and told it was up together, and got a new coolant sensor for him to put on, (to darn awkward for me), he did but i got it back home and went for a bit of a spin and its flashing again, there is no loss of water or overheating problems or anything like that, could it be something as simple as a loose connection somewhere, would it be advisable to replace the connector which is on there.

Also, just noticed that it s not getting up to temperature, it seems to be running cold but does creep up a little, could this be something as simple as the temperature sensor.

Many thanks as always.

[Fritz]

I'm sorry but you are going to have to explain this bit of your text...

I have had the engine serviced today and told it was up together,

WTF ,,,,

Regards,


Fritz,,,,,,,,,,

[Jutstar]

Yeah i know, went to a local guy and said i just wanted a service on the engine and after having issues with a previous camper wanted to give it a good going over. He serviced it plugs, filters etc but due to time limits couldn t sort the temp issues.

[AngeloEvs]

There are two inter-connected circuits for the cooling system wiring, one for the temperature and the other for coolant loss. The LED flashes if the temperature is high (not your problem given the gauge is reading low) or if the Level Sender Control Unit senses loss of coolant via the sensor in the header tank. A poor Earth will cause continual flashing and the most likely problem. Circuit diagram shows where to check and what. Colour codes should be right for your van. Easy check......remove the LSCU (looks like a relay and in position 3 in the fuse box , marked 42 or 43). Switch ignition on and if LED stops after initial self test then the fault is most likely in the wiring to the coolant Level sender.

[Jutstar]

Thanks very much for your reply AngeloEvs it is very much appreciated when i find out the problem with a simple test that i can do.

I did the test and yes it appears to be a problem with the wiring i m not confident it doing the wiring so will wait till it goes to the garage next time.

Thanks again

[gti mad man]

I have a similar issue after say 2hrs driving the led flashes but leveles fine and so is the temp? any ideas

[asahartz]

[quote="AngeloEvs"]There are two inter-connected circuits for the cooling system wiring, one for the temperature and the other for coolant loss. The LED flashes if the temperature is high (not your problem given the gauge is reading low) or if the Level Sender Control Unit senses loss of coolant via the sensor in the header tank. A poor Earth will cause continual flashing and the most likely problem. Circuit diagram shows where to check and what. Colour codes should be right for your van. Easy check......remove the LSCU (looks like a relay and in position 3 in the fuse box , marked 42 or 43). Switch ignition on and if LED stops after initial self test then the fault is most likely in the wiring to the coolant Level sender.

Ah cheers, that's a really useful diagram for me right now - having fitted an alternative engine I was trying to work out how to make the gauge (which currently seems to work in reverse!) and LED do something sensible! Now at least I can be on the right track.

[AngeloEvs]

GTIman, if this is occuring after the van has been warmed up then it could be any of the following listed below. Be aware of the following though as it may help your diagnosis. If the coolant temperature sensor falls below 50 ohms (due to high coolant temperature) this will trigger the LED but it will extinguish once coolant temp. returns to normal. However the coolant level circuit is more complicated since any problems here will cause the LED to flash until the ignition is switched off. Bear in mind how this part of the circuit functions. The Level Sender Control Unit sends a stream of pulses to the probes in the header tank. It expects to see a resistance of about 60K but if this resistance increases, due to loss of coolant, then the LSCU sends another set of pulses to the temp gauge and the LED is triggered (by the temperature gauges internal circuit). From the above it becomes apparent that any poor connections in the level sender circuit will fool the LSCU into thinking that there is a loss of water.

1. Poor connections in the Level sender circuit are the first things to check (see diagram above for location points)

2. Poor/intermittent earth connection at pin 3 of the Intrument housing multipin connector.

3. The LSCU is very sensitive to sudden voltage fluctuations in the coolant temperature sender circuit. A duff Voltage stabiliser can cause these symptoms (10V + or- 0.5V) as can poor connections at the temperature sender.

4. The coolant level sensor. This is just two probes that sit in the header tank but worth removing and examining for contamination, not connected to their relevant connector pins, etc.

5. VAG state that incorrect antifreeze mix will trigger flashing LED syndrome. Their service bulletin states that AF must not exceed 60/40 mix as it causes the coolant to have an excessively high resistance. I tested this out and connot confirm their findings but best to mention it.

6. The LSCU. This contains an electronic module and could fail after a couple of hours of normal use. Available new for around £25-00 and a couple of quid from Vdub shows second hand.

7. Unlikely but a small capacitor on the Instrument PCB intermittently failing could cause the LED to flash.

If I have missed anything out then hopefully others will add their comments.

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