[RiGOD]

Been happy with my 9 year old Fiesta Diesel it has hardly given me any headache till date.

So one fine morning while driving to office, I noticed that the temperature gauge gradually making its way to maximum. But to my surprise, the engine was running smooth and there were no signs of trouble. By the time I parked the vehicle, the temperature gauge hit 120 degrees and the radiator fan kept running for a while after the engine stopped.

Took the vehicle to FASS and it's been two days and they still can't figure out what's wrong. They checked the coolant temperature sensor, thermostat, the associated wirings and socket. Everything seems to be fine. Still, after driving around 6kms, the temperature gauge hits maximum and the car shows no signs of trouble. Could someone help me out here?

[dhanushs]

It's very unlikely that its a temperature guage malfunction. Also, a risky proposition to think like that. So, please dont continue running the vehicle like this, and figure out the root cause. It can be but not limited to Water Pump, Coolant Leak, Gasket failure.

[GForceEnjoyer]

I think you might have a genuine overheating problem, because I doubt that a malfunctioning temperature gauge would do this. If it is indeed a gauge malfunction, the exact coolant temperature reading on the diagnostic menu in the MID is likely to be different to what the gauge shows. (To access the menu, keep the odometer reset button pressed for a few seconds after turning the key to position I. One of the displays will show you the exact coolant temperature. Source: (My 2015 Ford Classic 1.6 Titanium)

https://youtu.be/t0IERgK_E_k?feature=shared

Does the gauge take a normal amount of time to reach operating temperature and then just keep climbing? If so, that would probably point to a problem with the cooling system. It could be a simple coolant leak, or something wrong with the thermostat/water pump.

It could be that the thermostat is not opening properly (it is a valve that's supposed to slowly open to let coolant flow to the radiator and back once the engine begins to warm up).

This is all I can say with my layman's knowledge of cooling systems, but if your service centre is unable to find out anything at all, it might be time to reach out to a different workshop.

[RiGOD]

Originally Posted by dhanushs

It can be but not limited to Water Pump, Coolant Leak, Gasket failure.

The coolant level remains unaltered so it shouldn't be a leak problem. Will ask the FASS guys to check into the other two possibilities.

Originally Posted by GForceEnjoyer

I think you might have a genuine overheating problem, because I doubt that a malfunctioning temperature gauge would do this.

Could be, but my doubt is, if it's indeed a heating issue, shouldn't the dashboard throw up some alert or even the engine stall to prevent damage?

Originally Posted by GForceEnjoyer

Does the gauge take a normal amount of time to reach operating temperature and then just keep climbing? If so, that would probably point to a problem with the cooling system. It could be a simple coolant leak, or something wrong with the thermostat/water pump

The temperature climbs up slowly and stays steady at normal values for quite some distance. After sometime it suddenly shoots up to maximum.

The service centre guys updated that they're suspecting a radiator blockage and hence dismantling the whole unit to find out. This is taking longer than usual

[TheCamShaft]

Originally Posted by RiGOD

The temperature climbs up slowly and stays steady at normal values for quite some distance. After sometime it suddenly shoots up to maximum.

Also might be a good idea to check if radiator cap valves are functioning correctly.

[tsk1979]

Originally Posted by RiGOD

The coolant level remains unaltered so it shouldn't be a leak problem. Will ask the FASS guys to check into the other two possibilities.

Two things

1. How do you know the coolant level is good. Did you open the radiator when cold?
2. When it goes high, go outside and look at the fan, see if fan is on.

If these two things are not the problem, it could be a water pump failure which is intermittent, or thermostat. Thermostats can go bad often.

Do you lose air conditioning when this happens?

[asit.kulkarni93]

Ford diesels are notorious with fan motor related issues. But in this case, Before you check the electricals please get the radiator cleaned followed by replacement of the thermostat. Please check all the coolant hoses for minor leakages. Then you can check the fan motor resistor and sockets. The ford dealer on their scanner excute actuation tests for the fan. Lastly, you will have to check the Meter cluster too.

[GTE]

You need to check (very carefully) the difference in temperature between the upper & lower hose pipes. If there's a significant difference it is probably a broken water pump impeller.

[RiGOD]

Originally Posted by tsk1979

2. When it goes high, go outside and look at the fan, see if fan is on.
Do you lose air conditioning when this happens?

Yes the fan stays on quite some time even after I stop the car. As for AC, I always drive with AC off. So no idea.

Originally Posted by asit.kulkarni93

Ford diesels are notorious with fan motor related issues. But in this case, Before you check the electricals please get the radiator cleaned followed by replacement of the thermostat.

The radiator has been cleaned and still the problem persists.

Originally Posted by GTE

You need to check (very carefully) the difference in temperature between the upper & lower hose pipes. If there's a significant difference it is probably a broken water pump impeller.

So I took the car to another mechanic and he asked me to drive till the the meter hit maximum (which took about 5kms of driving). I did so and then checked the radiator hose. The upper hose was cold and the lower one was slightly warm. What does that signify? He told it's possibly a failed thermostat. But again, no warning lights, no unusual behaviour from engine etc.

[sagarpadaki]

Originally Posted by RiGOD

So I took the car to another mechanic and he asked me to drive till the the meter hit maximum (which took about 5kms of driving). I did so and then checked the radiator hose. The upper hose was cold and the lower one was slightly warm. What does that signify? He told it's possibly a failed thermostat. But again, no warning lights, no unusual behaviour from engine etc.

He is right. Changing thermostat should be the first option you should try. Unless physically broken, there is no way you can verify if a thermostat is working properly by visual inespection.

It is good idea to replace thermostat at 1 Lakh kms or 7-8 yrs mark as preventive maintenance.

Before tearing apart anything, get the thermostat replaced to see if the problem goes away.

[GTE]

The thermostat CAN be checked by lowering it into boiling water & seeing if the valve opens. If the waterpump is easily accessible it should be opened & checked.

[PreludeSH]

Had issues with my 2011 Vento diesel. Changed water pump, thermostat, hoses since one was leaking during to high coolant temperature. Nothing helped.

The last thing, the radiator was changed and now its fine. I used to hit 120 degrees regularly after some driving in high traffic and the worst thing was AC cutting off during that time.

[GForceEnjoyer]

Originally Posted by RiGOD

Could be, but my doubt is, if it's indeed a heating issue, shouldn't the dashboard throw up some alert or even the engine stall to prevent damage?

Well, this varies across models, but your car does not have any. The Fiesta has a dedicated analogue coolant temperature gauge, which means there is no need for a separate warning light for overheating, which is why there is no other alert (cars without a coolant temperature gauge have this).

And no, there is no fuel cutoff to the engine in case of overheating. The engine will run until it physically cannot anymore, which makes it all the more important to turn off the engine as soon as possible if it overheats.

We have a Fiesta 1.6 petrol which once overheated, and in addition to the coolant temperature gauge moving beyond 90°C, the throttle response became strange, where it felt like there was a lag before throttle inputs had any effect. Since this occurred in peak traffic in the summer, the coolant had already boiled over by the time we could safely stop, with steam pouring from under the hood. (The cause was a leak in the hosepipe that caused all coolant to flow out.)

No damage was found at the time, but then the head gasket failed prematurely at roughly 55k kilometres, and we're pretty sure that the overheating incident was the reason for this. Hence, finding someone who knows what they're doing is very important, and please refrain from driving the car until it's fixed. Good luck.

[Jeroen]

Originally Posted by RiGOD

So one fine morning while driving to office, I noticed that the temperature gauge gradually making its way to maximum. But to my surprise, the engine was running smooth and there were no signs of trouble. By the time I parked the vehicle, the temperature gauge hit 120 degrees and the radiator fan kept running for a while after the engine stopped.

Took the vehicle to FASS and it's been two days and they still can't figure out what's wrong. They checked the coolant temperature sensor, thermostat, the associated wirings and socket. Everything seems to be fine. Still, after driving around 6kms, the temperature gauge hits maximum and the car shows no signs of trouble. Could someone help me out here?

A couple of thought. First of all the image doesn’t show the temperature maxing out. It looks it is at about 100oC? As such on a modern pressurised system not a problem. The red area on your gauge is in the 115-120oC. As the system is pressurised the coolant boils at a much higher temperature than the traditional 100oC. Now if it has always been lower and now shows 100-105oC there is something happening, but unless it really hits the red area on your gauge there is no immediate concern. If it does you should stop immediately and not restart the engine till this problem is sorted. As others mentioned there is no auto protection that shuts down your engine due to high temperature.

It was also mentioned that you would not have a red overheating warning light as your Fiesta has a temperature gauge. That could well be true, but our European Fiesta has both. And in fact all my cars, with the exception of my Mini Have both.

Check your owner manual if you have such additional red overheating light. Because if it has not come on, it is good news too! The temperature gauge and the red light have two separate sensors and wiring.

I have noted that your FASS has tried to diagnose the problem and was not able to find the problem.
But how did they check verify?
How did they test the thermostat? You need to remove it and heat it up in a pan of water and check the temperature at which it opens and measure how far it opens.


There is an easy way to check whether the thermostat opens. You need to start the car from cold and drive at a steady speed. You will the the needle on the gauge rising as the temperature goes up. When the thermostat opens, you should notice the temperature drop for some 5-7oC and subsequently go up again a bit.

I took this (poor) video of the temperature gauge in my Jeep Cherokee. Once it hits 120oF you see it moving back and gradually coming back up. This is the exact moment the thermostat opens. If you drive your car, at a steady speed, and the temperature of the coolant keeps rising at a steady pace, it is likely something is wrong with the thermostat. There could be other reasons, but thermostat are known to break after a number of years.

https://youtu.be/5xyLKrZVk4s?feature=shared

How did the they the coolant temperature sensor. Again, the only reliable way of testing is to remove it and warm it up in a pan of water and checking the change of resistance.

How did they check the wiring? You need to verify continuity and resistance of every single wire in the circuit.

Did they check for error codes?

There are several other tests that could be done, but you need a good reliable Infra Red thermometer. That is the most reliable way of testing the complete cooling system for problems. It should give some ideas
Of any restriction, possible air pockets and so on.

As other have mentioned there might be a problem with the coolant pump. You need to open it up to check. The rotors of these pumps tend to corrode over time which means the volume of coolant pumped becomes less and subsequently the temperature of the system risks.

Radiator blocked is also possible, again, you need to remove at least the in- and outlet hoses to check it.

Lastly you could be suffering from small/partial head gasket leak, or maybe even the engine block. If so there are usually tell tales in the expansion tank. Can be tested by performing a full coolant pressure test. That might not be a bad idea anyway given this particular problem

Good luck
Jeroen

[tsk1979]

Originally Posted by RiGOD

Yes the fan stays on quite some time even after I stop the car. As for AC, I always drive with AC off. So no idea..

My other question, how do you know the coolant is low.