I just did my summer t-stat swap on my '82 vanagon with the 1800 I4 engine.
I use an 87C t-stat during the winter and a 80C unit in the summer.

It won't come as much of a surprise to anyone that the "cooler" t-stat
lowers oil temps during hwy (70mph) driving. With the 87C unit oil temps
would climb to 115-120 after about 30 minutes of driving at 70mph. Water
temp would be steady, with the needle at a position just above the led. Now
the oil temp is 103-107 and the water temp  needle now lying just below the
led.

BTW, I didn't bleed my system after doing the switch. I clamped the hoses as
well as I could and replaced the spilled coolant (orange longlife blood). No
indication of much air trapped in system.

This in preparation for trip to Dinosaur prov park where I hear the temps
were recently in the 40s.

Alistair