I bought a '90 today and an odd thing is the temperature needle takes forever to get into the normal band and when it does, it stays right at the lower limit and sometimes dips below. My '89 always stays right in the middle. I checked the wiring to the temp sensor and the loom had been split open and the black wire was cut and reconnected. The other wire is yellow and green I think. So I guess someone else was trying to figure out what was going on, too.
The overflow tank is nasty with sediment so obviously it needs to be flushed out. Definitely a new thermostat and maybe a new water pump.
One more issue is valve ticking noise.
Other than that it's in pretty good shape. 104,000 miles, no squeaks, good power. I guess it needs a timing belt because I don't know the last time that was changed.