'04 Passat temp guage mystery

Today, while taking a brief 15 mile trip in our '04 Passat, the temp gauge shot up to high and the “Turn off the car” warning message appeared. I pulled the car to the shoulder and all of the sudden, the engine still on, the temperature gauge dropped back to normal. Checked under the hood and under the car - no leaks. Got the car home without the gauge rising again.

Later, I took the car out for another short drive to see if I could replicate the problem.

Two things I noticed: Even after sitting off for 90 minutes, the gauge jumped to the mid-way pt.(190 degrees) right at engine start. Five minutes into driving, sure enough the temperature on the gauge started to rise midway to high, and as I slowed down to turn off of the road, the temperature on the gauge dropped back down to normal. Checked again under the hood and under the car - again no noticable leaks. And again, I was able to get the car back home without the gauge rising again.

Normally, with the bobbing gauge, I would think I’m probably looking at a thermostat replacement. But this thing with the gauge shooting up midway immediately on engine start, even after the car has had sufficient time to cool, has me baffled. Even 2-1/2 hours later, I go out to the car and start it, and the temp gauge is immediately at about 120-130 degrees.

Can the car hold this much heat so long (it’s only mid-60’s here in Baltimore) or am I possibly looking at a more likely faulty gauge than a faulty thermostat?

Any advice or info prior to getting to the shop tomorrow is welcome. I would hate to pay for a bunch of unnecessary repairs as the repairman fishes to find the problem.

Many thanks,