Erratic temperature gauge after thermostat install

Hello again.

I thought I would open a new topic as it's a new problem.
I have changed the thermostat and sensor on top of it as it was not working as specified ( cold 70 degrees while driving) and there was a lot of pressure in the circuit.
Plus one time it gave me injector light and fans started going at full speed so from what I've read this might solve the issue

After I changed it with a new one( offered by Eurocarparts) the temperature gauge went slowly but surely above 110 degrees and no fans kicking in.
After changing it I noticed that the Radiator is not getting worm and only a small part of the hose coming from thermostat to radiator is getting warmish.

I have replaced the thermostat sensor with the old one thinking that the sensor might be bad.

Started engine and it took ages to warm but once it got to 90 degrees stayed there for a few sec and then jumped all the way to 130 at which point I panicked and turned off the engine.

Coming after about 40 mins lated to the car I just put the contact and turned the key to see if the engine cooled down.

At my surprise I saw the temperature gauge fluctuating erratically and quite fast between 40 deg and 110 with unsymmetrical oscillation .

Again the radiator does not get warm but only a small part of the hose from thermostat.

I am lost as now the car has the old sensor back with only the new thermostat.

Is it my water pump though the cam-belt kit and pump were changed in 2014 (Ex owner with bill to prove- but then again I have seen so many that lie)?
Is it a dodgy thermostat ?
I am completely lost.

Engine is not smoking white.
No gases in the water tank.
No mayonnaise.

Have any of you had this symptom ?


Regards,

Cip

Make sure the plug/socket for the temp sensor is dry and hasn't been splashed with coolant as that'll give an erratic reading if wet.

If it's dry try a test by unplugging the sensor. With it disconnected the rad fans should start running at high speed and bring an injector light up on the dash.

Thank you,

Will check it as soon as I can. But doesn't the coupe have two temperature sensors?
One on the block and one on the thermostat ?

The thermostat one only controls the fans and the block one gives the temperature to the gauge right ?

Also there is the issue with the new thermostat where the radiator does not get worm even after 90.

The thermostats are set to open at 86 degrees, the reading on the dash shouldn't be trusted as I've known them to be +or- 10 degrees when measured against a diagnostics reader.

The late models only have one water temp sensor which is the grey one in the thermostat, it controls ECU signal and the dash gauge, early models had a separate red sensor in the end of the head.

Erratic dash readings can also show you have an airlock somewhere, probably the heater matrix.

Mine has a 3 pin grey sensor so I assume that it only has one.

Based on that I still cant understand why the radiator isn't getting hot after 90 degrees unless there is a malfunction with the new thermostat or water pump is not working

Did you ever come across this issue ?

IT's a 16V, Joe; the fan is controlled only by the switch on the radiator. If hot water isn't getting to the radiator the fan won't come on.

It does sound like either the new thermostat is stuck shut or the water pump isn't pumping.

You havnt got a air lock have you ? The bleed screw is on the top left of the rad ?

Hello

I know and have tried bleeding the radiator but f the engine is cold the thermostat is closed so will the water go in the radiator?
Also what if I have an airlock at the thermostat where the temperature sensor is? how would I eliminate that?

For Barnacle:

the signature 16VT represents another coupe I have.
The discussion is about a 20VT plus

On Tuesday I will take te new thermostat off and boil it to see if it opens.

Still open for ideas.

Regards,

Cip

There is also a bleed point on the matrix feed/return pipe just behind the battery, round plastic plug in the centre of the pipes, just don't drop it.

You won't have an airlock in the thermostat, not possible, also can't see boiling it really being a conclusive test tbh.

Check for airlock, run the engine up to temp and keep an eye on the dash gauge feeling the top coolant hose feeding the rad. This should stay cold until around 80-90 degrees at which point the thermostat will open letting it circulate coolant through the radiator.

Hello,

Did the boiling test on the old thermostat and to my surprise it opened at 70 degrees(not normal I presume)

On the new thermostat it does not open even after 90 degrees.

How do I check if the water pump pushes the coolant?

I see that the small hose going on top of the water tank is feeding the tank with small quantities of water so I assume that some circulation I do have since that water manages to climb on top of the engine and then drip in to the tank.

I will also check the new thermostat to see if it opens but I have to remove it first.

Tricky little situation.

You should see a constant trickle of coolant returning to the expansion tank, more so when it's revved.

Do you know the history on the water pump and radiator and when they were changed last?

Well,

The cambelt kit was changed in late 2014 and I have receipt for that. However I do not know if they changed the water pump as well as it's not mentioned.

Radiator has been recently changed as it looks new.

To be honest I do not trust the last owner as it was one of those types that does not care about the car.

I will do cambelt as well but for now each step at a time.

I changed injectors
Filters and oil
Bought various bits that were missing
Changed Turbo with uprated 360 degrees bearings and polished intake.
New battery
Cleaned all the rust and various dents it had( still have one bonnet dent to fix)
Added DS vented fenders as the old ones were rusted dead.
Rewired the stereo as it was not working
Cleaned heater blower contacts and wire connections.
Added the speed variator (was missing)
Spacers on the rear wheels
Bonnet strut as one of them was missing

So I was stuck for about two months in the garage with the poor thing.

Now waiting to gather some more funds

Hello all,

To update on the curent situation.

I replaced the thermostat with oe part and now car heats up well and managed to read with a friend using fiat ecu scan the temperature live.

Thermostat opens as should and fans kick in at 98 every time. Is that normal?

The problem is that the dash gauge is indicating 120 deg when the engine is in fac at 90.

Cleaned the connector so what could it be next?


Any reply is helpful as i need to fix it.

Regards,

Cip

Hello

Any ideas on the above ?

I need to take the coupe for a spin so please support

Cheers

Check there's no signs of water or tarnishing on the main ECU plug connections, it might of suffered water ingress from a leaking screen.

Ok

Will check that.

Also just as a mention I have only the 3 pin connector for the temp sensor and no plugged sensor in the engine head but a blank cover screw.

Can someone tell me what the three wires do ?

Which one gives the gauge reading?

Can the sensor be faulty in such a way that it gives the correct ECU reading but the wrong Gauge reading?

It is a new sensor that I bought with for the thermostat and is FACET brand.

Hello,

I think topic closed and problem solved. Thanks Jamie (Todger182) for the support and work along the way

Finally I had to re-calibrate the dash gauge.

Car indicates and sits perfectly at 90 degrees on the dash and ECU scan saying 90-93 constant and 98 first speed of fan kicking in.


Regards,

Cip

That's interesting, how did you re calibrate the dash gauge?

Well no easy way.

I had to take the instrument binnacle out and mark where it sits after removing the limiter pin. I then pulled the indicator pin (slow and many prayers) and re-positioned it subtracting the amount that it was above the normal value(my case about 25 degrees. I saw on the indicator the amount of rotation it needed to coincide with 25 degrees C and carefully positioned it so that it indicates the ECU given value.

While I was there I changed also the dash speedo as mine was faulty so I took it from a donor dash.
From what I noticed the cars dash had some surface oxidation on the wires so cleaned all that.

I so happy now as fiat is running better then ever and pulling like a train.

Yeah but you know what they say, in Italy no-one grows up wanting to be a train driver