Temp Gauge only going to 1/4

Hi all, had a search on past posts but can't see anything quite like my fault. 

I have a MK1 Sportline and the temp gauge doesn't work properly - it does rise but only to about 1/4. It never goes above that. 

The fan does kick in but I don't think there's any logic to when. 

I did take it to a great guy and he fixed it by replacing a sensor that has wax in it - the wax wasn't melting properly so not opening  - does that make sense? 

He did all the usual tests like putting an electric current to the wiring and the temp gauge needle shot up to max so everything looked ok there.

It's failed again but the guy I went to lives quite a way from me so thought I'd try myself but I don't know which sensor etc to look for. If it helps the MFA stopped working about the same time though this could be a coincidence! 

If anyone has any photos / part numbers etc to look for that would be amazing 👍🏼

Any other info needed just let me know!

Thanks
Jon

Should also mention, not sure if it's relevant but there's no heat coming out of the heater even on level 3 fan. 

Related maybe?

Sounds like thermostat has been changed, it restricts water flow to the rad to enable the engine to warm up to operating temp quickly.

It may have failed again and allowing water to flow and never warm up the engine?

If you drive somewhere in this warm weather reving its nuts off in 2nd or 3rd it should warm up? Surpised the rad fan is working if the temp never rises?

The heater fan will still blow cold if the water is not warm and/or the valve in the engine bay connected to the temp lever in the cabin isn't working

The sensor for the temperature gauge has no wax which melts in it.

The thermostat does have wax which melts then opens to let coolant into the radiator when it reaches 88 degrees so the engine does not get to hot as the radiator cools the coolant.

If he replaced the thermostat the coolant would have been drained so has he replaced the coolant?

If he did replace the coolant there probably an air lock in the system as you said you have no heat coming out the the heater and that's what happens with an air lock.

To start don't worry about what the gauge reads just yet as you need to check which hoses are getting hot to eliminate an air lock.

Set the cars heater to hot and then check your coolant level when cold, leave the expansion tank cap off and give the top radiator hose a squeeze, you should see and hear coolant moving in the tank and possibly a jet of water from the thin coolant pipe from the radiator to the expansion tank.
Now with everything topped up and the cap still off start the car, you should see a small jet of water from the thin pipe into the expansion tank, if you rev the car (you can do this via the throttle body so can watch the tank) the flow of water should increase with higher revs. Give the top radiator hose a few squeezes and watch the coolant level you may find the level drops as the air is coming out of the system do this a few more times watching the level and make sure the tank does not empty and top up as needed to the max level with the engine still running put the cap back on when the levels have settled.

Now carefully as things are spinning around and starting to get warm feel the coolant hoses, the hose from the side of the engine (right hand side when facing the engine) should be getting hot 1st, this hoses goes to the cars heater.
The top radiator hose should also be getting hot and when the thermostat opens the bottom radiator hose will get hot filling the radiator with hot coolant then when the radiator is hot the fan should kick in.
Just make sure you don't over heat the engine if there is a problem the new thermostat.

When the fan has kicked in and then stopped switch the car off and leave it for serval hours to cool before removing the expansion tank cap and checking the coolant level.

What colour coolant did the chap use as not all coolant is compatible with each other?

Wow that's great advice guys thank you! I'll check tomorrow and let you know 👍🏼

make sure the ground from the right rear corner of the valve cover stud/nut is attached or affixed to the coil bracket.  This sets up the ground for the MFA.

The only wax in the entire system is internal to the Thermostat.  If you changed the a/f (coolant) and didn't either drill a 1/8" hole in the lip of the t-stat or properly refill the system then you can have a air bubble from hades.

To refill your system in the future drill the hole in the t-stat lip then no worries as the air bubble is allowed to pass.  With out drilling, you have to open the heater core to max hot.
From the upper hose of the radiator which is loose on both sides, fill from the hose to the radiator until water spills out the edge of the upper hose connection.

Reverse the hose and fill from the hose to the block of the engine through the upper water outlet.  Once it is dribbling out then replace the hose on both the upper radiator and the engine outlet and tighten.  

Start the engine, and fill the expansion jug, cap stays off until the a/f or coolant starts to leave the expansion jug, once the fan has cycled one time turn the car off, an let it cool, top off the res as needed and Cap.  Your car should be serviced well and all should be right with the world.  

On all my cabbies the gauge in the clocks usually only reaches a little over 1/2 deflection or about a needle over the red light.

https://vwgolfmk1.org.uk/forum/index.php?page=topicview&id=classifieds%2Fparts-wanted_2%2Fvoltage-stabiliser

The voltage stabilzer on the back of the instrument cluster can cause your issue. Mine does the same at the moment. It's pretty easy, and cheap, to replace.

If his fuel gauge works then it isn't the 10V stabilizer.
He states that the meter fully deflects when jumpered.

You can jumper the sender connection  and use a 9V battery, Jump the Positive side to the connector on the sender, and ground the negative side to the frame.

I have the exact same problem!
All the hoses heat up as they should, not losing any coolant.  The only time the temp gauge gets anywhere near the middle is when it’s sat still with the engine idling, then the fan kicks in no problem.
If I then take it out for a drive the temp drops rapidly and kicks out almost no heat from the vents. Tried keeping it at high revs in low gears and that does nothing to the temp at allNo other problems with the car apart from from a reluctance to start if it’s been left a while but I think that’s down to the fuel pump/accumulator

Maybe it’s a dodgy coolant sensor or the connection on top of the sensor is a bit furred up?

Has someone removed the thermostat?
The bottom radiator hose should be last one to get hot.

Thanks all, so  I had a few mins to play around this afternoon… 

Did the coolant tank check, jets of water coming through when the hose is squeezed and also when the car is started and revved. 

The 2 pipes connected to the rad (circled in red on my photo) got hot very quickly, couldn't see the pipe on the right mark1gls was talking about that should get hot 1st. All the pipes on the right (in blue) stayed cold

Left running for 10 mins, those 2 pipes got too hot to touch but the fan hadn't kicked in yet.  

Coolant is pink if that matters?  

.   

Jon H said

Thanks all, so  I had a few mins to play around this afternoon… 

Did the coolant tank check, jets of water coming through when the hose is squeezed and also when the car is started and revved. 

The 2 pipes connected to the rad (circled in red on my photo) got hot very quickly, couldn't see the pipe on the right mark1gls was talking about that should get hot 1st. All the pipes on the right (in blue) stayed cold

Left running for 10 mins, those 2 pipes got too hot to touch but the fan hadn't kicked in yet.  

Coolant is pink if that matters?  

.   

Theres a lower rad hose below your top 'red' one, initiially this should remain cold/cooler than that top hose. As the engine heats up and then become hot (along with the top hose) the thermostat opens and the bottom hose becomes hot as the water flows around engine and rad. If the lower hose warms up at the same rate as the top one the thermostat is stuck open or missing.

The hoses you have highlighted blue are air intake and breater hoses and not water hoses and so will be cold/ambient temp

Ah thanks! That'll explain it 😂. Showing my lack of knowledge but learning as I go on has been fun! 

Added a pic of the coolant too.

I'll try to leave the engine running for longer tomorrow, check the bottom hose on the rad and see if the fan kicks on. 

Seems odd that it didn't today as the 2 hoses were too hot to touch! 

 

There is only 1 coolant hose coming out of the right hand side of the cylinder head. It's above the gearbox.

Ok so found all the pipes needed… the order of them heating up goes:

- small pipe from coolant tank to rad
- top big pipe from rad to engine block. 
- large pipe on engine block on the right hand side (the one I couldn't find before).

I left the engine running for 5 mins and the pipe at the bottom of the radiator was stone cold. Took the car for a drive for a couple of miles, came back and the bottom pipe was boiling then too. 

Still no fan on thought. 

Maybe it's all working as planned? It's just strange that when I took it in to get looked at one of the parts was replaced (sure it was the wax bit), then the temp gauge stayed in the middle where I'd expect it to be. 

Now it's gone back to being on a quarter and never going above that.

I do think the engine gets that hot the paint is discoloured on the bonnet - is that a thing?