Partner Overheating Slow Warmup

Overheating and slow warm-up do point to thermostat issues. Have you checked the coolant level, and are there any visible coolant leaks around the thermostat housing or near the temperature sensor? Is the temperature gauge fluctuating wildly, or is it a steady climb into the red?

Coolant level is fine, no visible leaks. The temperature gauge climbs steadily into the red after a while, particularly under load. Is a defective map thermostat the most likely culprit in your experience? I've heard those can cause these symptoms.

Yes, based on the symptoms you describe and the absence of leaks, a defective map thermostat is the most probable cause. It's responsible for regulating the coolant flow. I would suggest taking it to a workshop and ask them to check the thermostat.

Thanks for the confirmation. I'll take it to a workshop. The estimated repair cost is around 350€. Sounds like a defective map thermostat indeed. Appreciate the help!