Recently bought this escort 1.8 tddi finesse, endura-de engine and I've noticed that the temperature gauge creeps up quite a bit when driving with the lights on, it's especially noticeable on fairly long journeys

I also have a gti escort which had a similar issue when I first got it and I cured that one by replacing the thermostat and thermal sensor so I thought I'd try the same thing on this one, but I can't find either on this engine

It's the first diesel car I've worked on myself so there's an awful lot I'm unfamiliar with

Anyone know if these even have a thermal sensor and/or thermostat? If so where might I find them?

Anyone know what else might be causing this behaviour where the temp creeps up with the lights on?

I'm not sure that the engine really is running hotter when this happens as there doesn't seem to be any effect on how the car runs

In case it's relevant, under normal daytime driving the needle on the gauge sits firmly at the halfway point and almost never moves unless driven REALLY hard