Master Overheating Sluggish Warmup

I had a similar issue with my old Vauxhall Astra, although it was a petrol engine. Symptoms sound identical – overheating and sluggish warm-up. Was the thermostat housing your first thought, or did other components get checked?

The thermostat housing was my main suspect, given what I've read online. I haven't really dug deeper than that, to be honest. Could it be something else causing these issues?

In my case with the Vauxhall, it turned out to be exactly that: the map thermostat. Given that you haven't checked anything else yet, I'd strongly advise getting it to a workshop for a proper diagnosis. They'll be able to confirm the issue and give you a firm quote before doing any work.

Appreciate the advice! Looks like I'm heading to the workshop. Will keep you posted.