Lots of good advice but.... no one has suggested that you determine exactly what you engine temp is during normal highway operation. My experience with older vehicles is....that they seem to run best at about 180 plus or minus a few degrees. Once you get an actual reading that is accurate you can start with the above suggestions.
Running a vehicle BELOW the optimum temperature can have an adverse effect on engine life and performance. I made this error by putting too much cooling w/160 thermo and wound up with contaminated oil that was below optimum operating temperature and cylinder wall wear that was excessive for the mileage. After doing some research I discovered that the wear factor was magnified by deviations above, but moreso by temperatures below the optimum for your engine. Since then, I've concluded that pre-cat engines are pretty happy at 180 and owning a hand-held infrared temp gauge is money well spent. Just my $.02 and I hope it helps because...
