Engine Temperature Guage Not Moving

Any ideas as to why my engine temperature guage isn't working, would be much appreciated. 

What I have done so far,  before I have become perplexed:)

1.Replaced ECU engine temperature sensor 
2. Tested single pin engine temperature sensor (multi meter readings drop, as the sensor warms up)
3. Replaced and tested engine coolant thermostat. 
4. Bled the air out of the water system to the point where fluid is coming out of all 3 bleed locations. 
5. Water is getting to and heating the heating matrix well. 
6. Hot water is felt at both  inlet and outlet rubber hoses to radiator. 
7. Hot water is felt and present at all cylinder head rubber hoses, (including the engine temperature sensor housing).

The only clue I have,  is the radiator fan isn't coming on, but it does if I unplug the ECU engine temperature sensor.
(however the rear engine fan is coming on).

Am I missing anything?

Any ideas would be most welcome. 

Thank you. 

I will assume you are aware that temp gauge has its own temp sensor. That sensor sits just below engine temp sensor on the same elbow. Since engine temp sensor is working as it should (you did not mention eny problems on that part) so temp gauge sensor should be working without problems.
You mentioned that you tested single pin temp sensor - I will assume that is gauge temperature sensor, since that is not engine temp sensor. Engine temp sensor uses both pins.

So, eiher you have faulty gauge temp sensor which although giving lower resistance when hot, might still be faulty, or you have problem in wiring-connectors-connection from gauge temp sensor to gauge itself, or you have faulty gauge.

There is no any kind of connection from gauge to engine ECU. Gauge temp sensor wiring and gauge itself is isolated electrical circuit from anything else.

Thank you, I did replace the horizontal sensor (which I believe goes to the ECU) with a new one and tested it before installing it.
I didn't replace the vertical sensor, ,(which I believe goes to the temperature guage on the dashboard) but did test it.
As per your advice, maybe the vertical sensor is faulty, despite me testing it.
Could this explain why the fan isn't kicking in?

I shall proceed to replace the vertical sensor, even if its just for the purpose of illuminating it from the problem.

Best regards
Daryl

Wild Rover wrote:

Could this explain why the fan isn't kicking in?



 

No, as I said vertical sensor does not have any connection to engine ECU. It only provides information to temp gauge.

Do you have any means to measure coolant temperature? Like "pscan" or any other application with dongle in diagnostic port? I am asking this to be able to see what information engine temp sensor is providing to engine ECU.

Tell me on which car you have this problems of coolant radiator fan not comming on? Is it on 1997 VVC MG F or different car?

Which fan?
I had an engine bay fan that did not appear to work. With power off I inserted a “stick” or rod through the car side vent and just rotated the fan a little.
Since freeing that off the fan has come on almost every time the car has been out.
I think I had a similar issue with the front and adopted the same methods/procedure. Both now function as they should.

Thanks for your reply unfortunately I don't have any means to test the water temperature.
Yes, it is the MGF VVC, but 1998.

I may have communicated incorrectly by calling the vertical, a temperature sensor, I do know this is just for the temperature guage on the dash.

It is starting to look like I have 2 unrelated problems, instead of 1.
My plan is to replace the vertical, to see if that activates the guage. If not, then as you say, that leaves wiring or the gauge itself, as the next suspect.

Regarding the front radiator fan not kicking in automatically (unless if I remove the plug to the horizontal sensor), I am still at a loss, unless if there is another temperature sensor that I haven't come across yet.

Do you know if the electrical connection at the radiator itself, is also a sensor?

Thanks again for your input.

Regarding any sensor/connection at the radiator. No I don’t.
However, if you are saying that if you connect/disconnect at the engine bay on the sensor positioned by the cylinder head and you can thereby turn the fan on/off it suggests everything else is working as it should I would have thought.

I have not had to change these sensors nor disconnect more than one. Is it possible to “mix them up” when re connecting them if both have been disconnected?

It takes at least 30 minutes on tickover from cold before my rad fans start. If you close the cabin heater valve the fans should come on slightly sooner but it still seems a long time while you are waiting.
It is definitely worth fitting a new 'vertical' sensor for the gauge before looking at more complicated things. 

Wild Rover wrote:

Thanks for your reply unfortunately I don't have any means to test the water temperature.
Yes, it is the MGF VVC, but 1998.

I may have communicated incorrectly by calling the vertical, a temperature sensor, I do know this is just for the temperature guage on the dash.

It is starting to look like I have 2 unrelated problems, instead of 1.
My plan is to replace the vertical, to see if that activates the guage. If not, then as you say, that leaves wiring or the gauge itself, as the next suspect.

Regarding the front radiator fan not kicking in automatically (unless if I remove the plug to the horizontal sensor), I am still at a loss, unless if there is another temperature sensor that I haven't come across yet.

Do you know if the electrical connection at the radiator itself, is also a sensor?

Thanks again for your input.

As said, if you remove plug from horizontal sensor and fan is kicking in that means engine ECU and wiring and relays work as they should. There is no other sensor for cooling fan to activate it. So you need to see what temperature reading sensor provides to engine ECU.

Update. 

I have removed the plug from the temperature guage sensor,  connected a wire to its pin   touching the engine block with the other end.
The temperature guage shot immediately to hot (This confirms wiring to.the guage is fine.

Bought a new temperature guage sensor, from discount MG. The correct part was delivered and fitted,  but still no movement on the gauge whatsoever. 

Can anyone see what I am missing?

At this moment it would be essential to be able to see what information engine ECU temp sensor is providing. If temperature reading on that sensor is too low, that would be the reason why rad fan is not engageing (it does not receive info that it should) but in same time it will provide info why gauge sensor is providing info to gauge that that temperature isnthat low that gauge is not moving. In that case you have blockage in coolong system or airlock which provides false information to sensors.
If you have anyone near you with pscan software to be able to log details of engine ECU parameters and temperatures that would be most helpful.