The problem with the temp sensor is that it monitors the water temp by being in the water .When water is lost this sensor is now in AIR so the tem displayed will drop but the engine is cooking !.  The sensor is on the thermostat housing block on the battery side of the engine. The later engines have two sensors one on the cylinder head but the best way is to monitor coolant level as if low you know the temp will only rise.

18 hours ago, Jeipii said:

Could one use an OBD scanner with display permanently set up in the car and some alarm set up in the display when engine temp goes over the normal limit? (the limit could be obtained by just normal driving and checking out how the engine temp behaves).

Does the OBD-port give more accurate engine temp reading than the Fiesta mk7 and 7.5 pseudo engine temp gauge that is almost always showing "normal" temp even if the temp is varying a bit?  Or is the problem with the inaccurate or laggy engine temp sensor? 

I have an UltraGauge to do just this. The “gauge” in the car is a non-linear indicator which shows an ECU moderated reading, that peaks too late to be useful. The OBD2 port will show the actual water temp so you can adjust your driving when the conditions require it. 

54 minutes ago, ThaiFiesta said:

 The OBD2 port will show the actual water temp so you can adjust your driving when the conditions require it. 

Only when the sensor is in WATER not when the coolant level is low and the sensor is then measuring AIR temp !

11 hours ago, 540itouring said:

The problem with the temp sensor is that it monitors the water temp by being in the water .When water is lost this sensor is now in AIR so the tem displayed will drop but the engine is cooking !.  The sensor is on the thermostat housing block on the battery side of the engine. The later engines have two sensors one on the cylinder head but the best way is to monitor coolant level as if low you know the temp will only rise.

Is the sensor somewhere in this picture? And yes, I can understand the problem that when coolant is gone the sensor is measuring air temp and it doesn't react quickly enough to the engine overheating. 

I think it could be possible to set up Ultragauge alarm just a tad over normal engine operating temperature so that when the coolant level is dropping in a slower pace, the Ultragauge alarm would be able to react to slightly higher than normal engine temp.

This might even work with the quick coolant loss since maybe you could set up an alarm for low engine temp also :D The temp is bound to drop dramatically from "normal level" when the engine has been heated up and suddenly it loses the coolant. Air heat conductivity is so poor. Not sure if this would still be already too late for the engine to be saved though...

On 11/03/2018 at 9:57 PM, Jeipii said:

I think it could be possible to set up Ultragauge alarm just a tad over normal engine operating temperature so that when the coolant level is dropping in a slower pace, the Ultragauge alarm would be able to react to slightly higher than normal engine temp.

This is how I have mine set up. 

Im still looking at a separate low coolant level indicator though. 

I also check my coolant level before I start off every day. It’s a pain but less than losing an engine.

On 13.3.2018 at 9:05 PM, ThaiFiesta said:

This is how I have mine set up. 

Im still looking at a separate low coolant level indicator though. 

I also check my coolant level before I start off every day. It’s a pain but less than losing an engine.

Btw, what is the temperature range of your coolant based on OBD-readings? How high does the temp go?

3 hours ago, Jeipii said:

Btw, what is the temperature range of your coolant based on OBD-readings? How high does the temp go?

I took the following readings. 

Bars. Temp.   Time

Ambient 30. No aircon

1.    50.       1:40
2.    58.       3:55
3.    66.       6:30
4.     74.      8:50

But I’ve seen it stay on 4 bars at 106 deg C. 

1 hour ago, ThaiFiesta said:

I took the following readings. 

Bars. Temp.   Time

Ambient 30. No aircon

1.    50.       1:40
2.    58.       3:55
3.    66.       6:30
4.     74.      8:50

But I’ve seen it stay on 4 bars at 106 deg C. 

Ok. The 106 C is a bit high for a "normal operating temp" at least based on what I've read. The sensor could be affected by the heat conducted from the engine though, since I believe it's positioned nearby the engine. That would mean that the actual coolant temp was a bit lower than what the sensor is actually reading as a temp. Have you ever seen 5 or more bars in the temp gauge? I haven't in my Fiesta, but it's been driven during winter mostly. Waiting for summer to see how it behaves then.

On 20/03/2018 at 9:41 PM, Jeipii said:

Ok. The 106 C is a bit high for a "normal operating temp" at least based on what I've read. The sensor could be affected by the heat conducted from the engine though, since I believe it's positioned nearby the engine. That would mean that the actual coolant temp was a bit lower than what the sensor is actually reading as a temp. Have you ever seen 5 or more bars in the temp gauge? I haven't in my Fiesta, but it's been driven during winter mostly. Waiting for summer to see how it behaves then.

I have seen it all the way to the top when my fan relay was faulty. It triggered the limp mode a couple of times. I didn’t have the Ultra Gauge then so not sure what temp. Ford reluctant replaced the fan relay after several visits where they “couldn’t replicate the fault”. I haven’t had a problem since. 

On 3/22/2018 at 9:16 PM, ThaiFiesta said:

I have seen it all the way to the top when my fan relay was faulty. It triggered the limp mode a couple of times. I didn’t have the Ultra Gauge then so not sure what temp. Ford reluctant replaced the fan relay after several visits where they “couldn’t replicate the fault”. I haven’t had a problem since. 

How long ago did that fault in fan relay happen? Have you driven a lot of miles/km since that?
 Could it been that the fan failure causes the limp mode immediately or does it happen after the engine gets heated up too much?