I've had exactly this, a sticky t/stat. Hope yours is the same.

The car might not be overheating. A faulty temperature sensor could cause an erratic operation of the temperature gauge and run the cooling fan, even if the engine isn't particularly hot.

Entirely possible it’s been a very small loss over a good length of time. You have to lean over and look into the filler neck to see the contents as the expansion bottle is stained internally. I’ll drive it tomorrow and see how it does.

If you can easily detach the reservoir and clean it out, I suggest you do. If the staining is mucky brown that suggests rust, and the coolant may never have been renewed. Used to be a common problem with Renaults as coolant changes were not on the schedule, so no-one did them.

(duplicate post)

Edited by Andrew-T on 07/08/2024 at 09:35