Water Temp Issue

My mk1 is a 1.8, 8v, weber carb version. I am wondering if anyone could offer some assistance with an annoying problem with my water temp constantly reading high to the point of the red warning light coming on. i am not losing any coolant and have had a new water pump, thermostat, temp sensors at front and bottom of radiator fitted and the fan cuts in as normal. Alos tried changing the clocks thinking it may have been the gauge but no success. Any help would be much appreciated cheers. 

Flushing and back flushing the Radiator is the first step.
Matching the Radiator Fan Switch in the Radiator to the t-stat is another.
Verifying that your Radiator Fan works is the Primary thing I would be worried about.

On the early MK1s they simply used the Radiator Fan switch to turn on the fan, Simple easy and worked.

Later on when they added a/c they used a 2 speed fan, and the A/C relay, so that when the a/c was chosen the fan automatically kicked on.

Towards the end (Cabriolet wise) in the 90's they added another relay to the mix, This relay worked in conjunction to the After run temp sensors.  
This relay was stuck in front of the battery on the left hand side of the fender on a bracket, and gets water logged and will either get stuck on, or not work.  As it is the main power feed to the fan.

I would verify that your fans works by jumping 12V and earth to the 2 leads.  If you have a 2 speed fan, then you jumper (as you look at it from the top….)
The earth is on the left and the other 2 are 12V+

The light blinking may be low coolant as well….
You haven't been loosing coolant?

And include if you have a single speed fan or Dual Speed and if you have a/c or not.  Even if the A/C was deleted we need to know.

thanks for your reply my cab is a 1990 and i am not losing any coolant and the fan works and cuts in but the temp gauge is at max by then. i do not have A/C

Are you running the correct coolant in the car too? Comma g48? A lot of people use the oat stuff because they get told that's for it but it's not? 
Flush the stuff out if not!! 
Ohh are you sure your head gasket hasn't gone due to the over heating too? 
The rad fan switch on mine screws into the bottom right hand corner of my rad, check there and see if you can order a new one for it, check the wires to the fan itself too mate ? Hope that helps 

thanks but as i'm losing zero coolant, i had ruled out the head gasket. i have fitted a new fan sensor and temp sensor (one at front of the block). Although the gauge rises to the max it doesn't actually seem to be overheating as the fan does cut in and back out which makes it a real head scratcher. There is another sensor at the side of the block but i dont know what it is for? Are there any earths which could cause a false reading on the gauge by any chance (clutching at straws).Ive also flushed and back flushed and top and bottom hoses get hot and heater blows hot air in the cabin,

Sensor on the side of the head is for oil pressure.
Have you checked the condition of the connector and wires on the coolant temperature sensor, check it's not just about hanging on by a few wires.

wires seem to be sound, do you know if the earth on back of rocker cover could cause this fault as i recently replaced the rocker cover gasket and painted the rocker cover so earth may be poor

The earth on the back of the rocker cover is a earth for the dash (yes it's odd being there) and if it's broken it causes alsorts of problems with the dash, like if you turn your headlights on the rev counter dies…

Might be worth cleaning up that connection but not sure if it's linked to the gauge.

Whay sort of temperature sensor do you have?
One like this?
http://www.ebay.co.uk/itm/MK2-GOLF-Oil-temp-sender-White-1-Pin-M10X1-T4-Golf-Caddy-Corrado-049919563A-/361446383240?hash=item5427e21e88:g:iL4AAOSw3ydV3au~

Since we know it is a 90, then do you have the Expansion tank at full mark, as there is a Sensor in the middle that if you are at the low end as you are running, the low coolant will detect and flash the light.

Those sensors get corroded (calcified) and then they don't register correctly.  You just remove it and clean the ends of the sensor with Sandy-type-paper and it should be good to go, it takes 27 or 28mm if it is stuck.

So when this is hot is it at the low mark?

hi mark1gls, i will try and run an earth wire from the rocker cover connector direct to the battery to see if any difference and my temp sensor is not the one you provided but is vw part number 251919501A. All other electrics / gauges are working ok .
Hi Briano1234, the coolant in my expansion bottle never moves from the full mark with no loss of coolant

Well, I see that they say replace the white with blue?
I have always seen that the water temp sender on my Cabbies were always black, that is even for the Digifant when I was rocking the plastic flanges from Hades.

I don't ever remember a "white" sender.

I do know that the Oil Temp sender (which is also black) is the same as the water temp sensor that I use now.  I have since converted to metal flanges, and have a "Black single pin" for the water temp, and a 16v CTS sender for the CTS.

I do know that water gauges do go flakey, as they can get cold solder joints that can affect the operation, which after replacing my 3rd one, I decided to figure out what is flaky, and created a how-to that is linked in the Archive section…  Since the Water temp gauge has 3 legs.  One is the signal in from the sensor.
One is the 10V stabilized voltage, the last one is ground.

The blinky light is also controlled from the solid state internal of the gauge, as well as the coolant level controller that is in the Fuse panel.

On a 90ish Digi, you can take a 9v dc battery, (key off) and connect it to the 2 pins on the sender socket and the water gauge should deflect to 3/4 to full scale.

I have usually found and I have taken a few apart that the gauge when flaky usually flakes out and goes to 0
then may come back on.

If your Fuel gauge is ok, then it usually isn't the 10V stabilizer, but it wouldn't hurt to test it to make sure you are at the right voltages.

I would also suggest that you add a new earthing to your cluster (Pin2 Brown)  Add a 3m Scotch Lok and take that to FRAME behind the cluster…

Earthed the rocker cover connector directly to the battery but no success so back to the drawing board unfortunately. I just can't understand how this can be so difficult to diagnose as the actual system is relatively simple which makes it even more annoying.

Briano the 'white to blue' sensor comment you mention refers to the ecu temp sensor, not the dash sensor.

there is no benefit for the running of the engine, but the blue sensors are considerably cheaper plus they fit into the plastic front flange which is much easier to source than the metal ones if you need one.

also the VW oil temp sensors are supposed to be white, and have a different resistance curve to the black coolant ones. aftermarket sensors dont always match VW colour coding however.

going back to the original issue, if you disconnect the yellow/red wire does the gauge stay at 0? check the sensor carefully make sure its black if genuine, and its all clean. if its pattern then this could be why, might be wrong or just poor quality.  have a good look around the engine for any brown/white wires, one of them is for the cluster if it has the MFA so this needs to be clean and tight.

hi rubjohnny, disconnected the red/yellow wired connector to the sensor as you suggested and the gauge remained at zero. The sensor is a brand new pattern part which replaced an original VW unit, so they are both either OK or N/G. Do you think i should replace the sensor again but with a VW sensor to rule it out altogether? Also mine does not have the MFA. Cheers

ok so the original sensor read the same as the new one you fitted? either you are unlucky or there is something else going on.

one thing to look at is the main engine & the gearbox earth point on these is in a poor location, vw put it on top of the upper gearbox bracket. corrosion builds up between as time goes on. on later MK2 onwards this was moved to a stud on the end of the rear upper engine -> gearbox bolt, much better.

to test if it is a block earthing issue run a jump lead between the engine block and the battery earth. if its still poor carefully clamp the jump lead to the sensor body and other end to batty./ if that sorts it you know the sensor has a poor earth thru the alloy flange so give it a damn good buff up.

if you disturb the bolts be sure to have a new seal to hand, and when loosening loosen and tighten each bolt gradually otherwise theres a risk you'll crack the housing

thanks again, i'll try the earthing checks tomorrow and let you know how i get on. Cheers

Unfortunately I did not have any success with the earthing checks and the gauge moved to max with the red light flashing after approx. 5-10 mins and the fan kicked in after approx. 20-25mins idling. Cheers

Just thought i'd let everyone know that i finally got my overheating issue resolved and as Rubjohnny had suggested i was just unlucky.
The brand new pattern part sensor which replaced an original VW unit turned out to be the culprit as it was N/G (what are the chances)!
Replaced with an original VW dealer part (still available) and hey presto overheating cured and the cab is sweet as a nut once again.
The moral of this story for me now is OEM is always king whenever it is still available regardless of the extra cost because it just saves loads of hassle and grief.

Cheers

Docc