Sorry that this has to be "one of these" threads were as my first post is a problem. So here goes, I am asking for some help.

Only recently bought the car. Shortly after noticed that the car does not come unto temperature properly. First of all I didn't think anything of it as it was very cold here in the UK, and it was my belief most diesels can take an age to warm up. However the car does something strange. After about 5-10 minutes there is hot air coming through the vents inside the cabin inside, the gauge will rise to around 1/8 (around 52C) but only when doing low speeds or sitting at idle. When the car is on the motorway, the gauge does not register and drops back down. 

After a good drive if I turn off the ignition, leave it 5 minutes, the temperature gauge is were it should be (Just under half way), but after starting the engine, around 1 minute later it goes back to showing as cold. 

Initially got the thermostat changed, had the coolant flushed, did the same. The car also is running a little rough once it comes up to temperature. There is no loss of coolant and the system has been bleed, you can feel that the pipes both on the upper and lower hoses is warm. I do not think its a water pump failure as there is hot air in the cabin. Is it worth changing the ECT sensor,  on the right hand side of the engine. (This is the 1.8 Lynx) or is there anything else I've overlooked.

I know that the display on the gauge or display is not faulty, as I have linked up a ELM327 scan tool and it reads the same temperature as the car.  MPG is down a little averaging around 43, with mixed driving currently. 

Any help or suggestions appreciated.

I'd say it was acting quite normal for this time of year in the UK.

My MK4 Foucs 2.0 Diesel takes at least a good 30 minutes of driving at over 50mph for it to get up to about 85C. In the warmer weather it gets up to 90C in around 15 minutes of just general driving around town.

On 2/11/2022 at 2:38 PM, unofix said:

I'd say it was acting quite normal for this time of year in the UK.

My MK4 Foucs 2.0 Diesel takes at least a good 30 minutes of driving at over 50mph for it to get up to about 85C. In the warmer weather it gets up to 90C in around 15 minutes of just general driving around town.

That was my initial thought too. But i recently did a 2 hour motorway journey and it still did not get up amywhere near even 70c. 

 

The thing i find odd is if i park after a good drive. Say goto a shop, come out 5 minutes later, as soon as i turn the key it shows a warm tempreture but will then slowly drop down after 1 to 2 minutes. (I dont have to start the engine). Gut feeling is its sensor related

On 2/13/2022 at 1:47 AM, Dadof3 said:

That was my initial thought too. But i recently did a 2 hour motorway journey and it still did not get up amywhere near even 70c. 

 

The thing i find odd is if i park after a good drive. Say goto a shop, come out 5 minutes later, as soon as i turn the key it shows a warm tempreture but will then slowly drop down after 1 to 2 minutes. (I dont have to start the engine). Gut feeling is its sensor related

Hey @Dadof3 did you fix your issue ? I have quite the same problem with my Mondeo MK4 1.8 TDCI, when accelerating or engine braking the temps goes down slowly and it's quite hard to make it to the halfway (90°C) with the diagnose test tool on the odometer, it never pass 75°C... I've changed the thermostat and also the coolant sensor but still having the issue ..

Is the radiator electric fan running ?

25 minutes ago, unofix said:

Is the radiator electric fan running ?

No it’s not running 

51 minutes ago, Timur said:

I've changed the thermostat

Is it the correct thermostat for a diesel engine. They always run colder than petrol engines.

1 hour ago, unofix said:

Is it the correct thermostat for a diesel engine. They always run colder than petrol engines.

Yes it’s the correct thermostat ..