Look at the white paper label at the front of the engine in the photo.
Now look straight to the right to where the hose meets the engine.

The hose attaches to the thermostat housing. The t'stat housing is attached to the head with two nuts.

I strongly recommend some PB Blaster to loosen up the threads on the two nuts before loosening. Reason is, they often are on there for many years and will get rusty. I loosened one once without using PB Blaster and broke the stud that the nut is threaded onto. I was lucky; there was just enough stud left for me to thread the nut back on. But now I never open up one of those without using PB Blaster first, unless it's one I've had open myself in recent memory.
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Sven: '89 245 NA, 951 ECU, expanded air dam to 7" from ground, forward belly pan reaches oem belly pan, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns, tach, small clock. Wifemobile '89 245 NA stock.