Coolant Gauge and Light woes

[robw09]

Guys and girls, another coolant light and gauge woe from me and would appreciate what step I should now take.

1990 Mk2 Golf GTi 8v engine code PB

A week ago or so I was getting the odd problem on start up, namely the coolant light would come on, but gauge was in the centre.  I checked the coolant levels and it was just below min.  So, I topped back up to just below max when the engine was cool.

However, my problems just started to get worse.  I would get random "spikes" of the gauge to max and the red warning light flashing.  Sometimes the gauge would remain at max for just a few seconds, but sometime for a few minutes.  It never seems to affect the drive and the oil temp seems fine.

Then a few days ago as soon as I put the key in a turn once (just before ignition) the gauge shoots to the top and stayed then on ignition with the light not going out.

So, I decided to perform a coolant flush.  I took all pipes out and gave them a clean and the rad.  Inspection of the flush led to nothing untoward....all looked clean enough.  Re-fitted pipes and re-filled with a mix of 50/50, "burped" system to remove any airlocks.

Blowers blow hot, appears to be no leaks, bottom rad pipe stays cool for couple of mins and then starts to warm up after a bit longer and the rad fan kicked in at the MFA reading 93 degrees for oil temp.  So, I think, and I do stress think, the system is generally ok and I have an electrical gremlin as I still get the same issue of the gauge going straight to max and the light not going out.  Though I did, after about 15 mins, get the gauge to move to about 1 third of the way up (reading cold, though the light stayed on) before it returned to max.

So, before I go off replacing sensors or taking into a local garage are there any checks I can do myself?

I believe it could be a few things, but I am no expert!

1.  Relay No 42 knackered 191919376A
2.  Water temp sensor knackered 251919501D
3.  Coolant level sensor knackered.  No part no.  Though the ones I can see on the net don't look like they have any chance of fitting in my reservoir....
4.  Earthing problem
5.  Clock problem...please no!

Oh, please treat me like an idiot  and explain anything fully as from the reading I done it may be a few things, but I don't fully understand....bridging, earthing etc

Below are pics of my sensor and reservoir just in case

Many thanks and patience!  As I am one frustrated and anxious GTi owner 
Rob

[X4MGS]

Could be any of 1-3 - But looking at your bottle and cap 1st thing I would do is replace both of those as it's a well known fault with later MK2's. Had the same problem with the wifes and sorted it when I fitted new ones...

[Jimmyrallye]

As stated as above change black expansion cap for a new blue one ,, i had problems of late of my coolant kept flashing but then my rev counter stopped working and now the light dosent flash at all so ive got a bad earth some were!!! As soon as i play with the wired and get my rev counter to work the light comes on from cold... So i need to fix my pikey wireing and a new set of clocks

[robw09]

So Ken, you think it is something to do with bottle as my problems have got worse since opening it!

When you say replace the cap and bottle, what with (obviously with another one!).  I mean with what type? I have seen the blue tops (non OEM) are they ok?  What bottle would it be?

BR
Rob

[X4MGS]

So Ken, you think it is something to do with bottle as my problems have got worse since opening it!

When you say replace the cap and bottle, what with (obviously with another one!).  I mean with what type? I have seen the blue tops (non OEM) are they ok?  What bottle would it be?

BR
Rob

Personally I would replace BOTH with Genuine ones from the dealers....

I think the bottle is still on Back Order, so at least get the Blue cap to start with....

As The self professed Genuine OEM Junkie that I am I would never fit anything else...

As I Fink all OEM parts are sprinkled with VW "Fairy Dust"... and a 2 year warranty....

[robw09]

Hi Ken, have you heard of a bottle/cap creating a similar problem to mine then?  I know it is a bit of guess work, but even 2nd hand tanks are £20.

I have part number 357121407 for the water bottle.  I presume this has the sensor built in?  Do you have part number for cap?  I think i will start with cap.....though somehow i don`t think it will solve it   

BR
Rob

[Gambit]

Just replace the black coolant temp sensor. And then see what happens

[robw09]

Hi Gambit, I get the sense that it is a trial and error with these type of gremlins   I will ring the stealers in a minute and see if they have a blue cap for the tank and a black temp sensor and will give them a go and see what happens.

[mk2bal]

Un plug black sensor next to blue one on coolant flange. Bridge the two pins in the plug together, using a piece of wire. Check gauge for movement, should go all the way to the top and stay there with light on. Remove jumper/bridge wire and it should lower back down. This proves the gauge and wiring work. Then if your coolant header bottle has a level sensor unplug that, and do the same test you did earlier, this should make the light go on and off on the dash as you short the two, and disconnect them again. these tests will hopefully show what the culprit is, either black coolant sensor or header tank level sensor at fault..

[oakgreener]

It sounds to me that you have either a faulty black temperature sensor, ie shorting intermittently. Or you have a fault in the wiring to the sensor. Try it with the plug disconnected as mentioned previously and if it goes away with it disconnected,try a new sensor.