Cool running engine


Wrench Pro
VW Polo 1.4TDI
i have a 1.8tdci mondeo mk4 59reg. The car engine temperature always fluctuates a lot. I have changed the thermostat twice and the engine coolant sensor is on the side of the engine in a dry pocket rather than in the fluid flow. I have changed this sensor as well. To rule out the gauge I have done an obd2 scan and the temp on the software reads the same as the gauge.

Have also checked the engine fan is not running when the car fluctuates towards cold side and it doesn't.

So I think I have ruled out the obvious.

Now to explain what happens. If I get the car warm and idle it the car starts to run at about 75cI.e. If I then Rev the engine You can see the temp needle go from 75c back towards 60c When driving the car temp does fluctuate and sitting in traffic it may warm up and then when driving
You see a sudden temp drop.

When I have changed the thermostats the engine does run warmer
For a month or So but does still fluctuate and then goes back to where it was on the cooler side.

I am baffled. The only thing I can think is that the thermostats I have bought have been from eurocarparts and
Maybe set at a different temp to the original ford parts. From memory the europary ones are set at 80c however the car always seems to run between 60 and 75c. I have never seen it run at middle needle temp of 90c.

Before I buy a ford thermostat are
There any other suggestions as I can't keep buying thermostats and not solving the problem.


Torque King
Rugby (expat Preston lad)
Merc C220Cdi Elegan

Every time I've seen behaviour like that it's because the thermostat is stuck open. So perhaps it is because you've got an incorrectly rated thermostat and its not closing?

I don't know if your 1.8tdci is the same as in my Focus, but in mine once warmed up the needle sticks at just past the vertical, at about 90c, and never moves.

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