Coolant Light Woes

[robw09]

Yeah it is bloody annoying!  Thought it should sit in the middle, but it is a least stable and once up to temp it does not move.

It is certainly running better now with everything I have done to it.

I will try bleeding again.   Running with expansion tank cap off and burping the pipes??

I get no lights now, so that is a good thing and I am happy it is not the head!

[VW BUSH]

These can be really tricky to bottom out and fix the flashing temp lights.
That's why when I used to have Mk2's with this fault I made sure the fan comes on, stat is working, level is correct, pump works and no leaks etc
You can drive the car if you know its all working and its just a light gremlin.
I even rigged a lamp to come on with the fan so I knew it was coming on properly.

[robw09]

Yeah, i am pretty 100% sure all is good now.  I will try burping and see whether it sorts where the gauge is reading.

[robw09]

So after replacing just about everything I am still having issues.  Waterpump, thermostat, temp sender, flushed system (twice), burped etc.  The only thing I have not replaced is the coolant reservoir sensor.

Car comes up to temperature (water) as I have described.  Drives fine and if I am moving I do not have a problem, but as soon as I am sat still for more than a minute or two the light starts flashing and the water temp moves on to the 3rd line, but not past it.  Once I am moving the light goes off again and the gauge drops to just under the 3rd line.  I know this is the wrong position, but I was going to ignore if I had no other issues.  Oil temp is between 82-86 under normal driving and I have not seen it go above 88.

I really don't know where to start with this now.  I am debating whether to replace the temp sender.  I think the garage fitted a non genuine one.  So, i was going to pop into my local dealer and get a genuine one.

However, can someone more knowledgeable than me number step through what I should check for by having the car just running on my drive.  What hose should be cold/warm/hot & when etc.

If anyone is in Lincoln/Newark area and is handy and is prepared to help please let me know.  I can travel out to you to make it easier.

[VW BUSH]

Change the tank sensor if its old or suspected to be duff.
It could be in the instrument cluster itself, good luck..
Temp sensors use two different metals to give different resistance and convert this to a temp signal.
If the wires break down or you get damp or a poor connection you get variable resistance giving you an iffy temp signal.
If you use the wrong sensor or connect the polarity the wrong way round you get all sorts of problems.
You need someone to go over your car with a fluke meter to check its all working correctly.

Start the car from cold and feel the pipes as they get warm, certain pipes will stay cold while others get hot.
Then you will feel the cold ones get hot pretty quickly as the stat opens
Then so long as the fan comes on and goes off and the oil temp remains normal/stable you are fine to drive.

[total stranger]

Sorry if I missed it but is the fan cutting in?

[robw09]

So.

Ran the car on the drive and came up to temperature, but just under the 3rd line rather than the second.  The bottom rad stayed cold as it ran up to temp.

After about another 3 or so minutes the coolant flashed and the reading was on the 3rd line, then the fan kicked in with the bottom hose now becoming warm/hot.

After about half a minute the coolant light stopped, the fan switched off and the temp line dropped just below the 3rd line.

Rinse and repeat there after.  Oil temp never went above 88.

I am baffled.  Firstly the temp reading is too high and i also don't get this repeated on off of the light.

[total stranger]

I wonder about the thermostat. Sounds like it's opening too late.

[robw09]

Hmmm, this is the thing.  I replaced the thermostat when I replaced the water pump.  Do you think that is what is causing the water temp gauge to go the third line?

[sparkplug]

  Here's a good guide from rubjonny
  http://www.golfgtiforum.co.uk/index.php?topic=33252.0