OK, Here is my problem. My '85 is eating coolant. But the problem is when driving around town, the engine temp stays normal. When I cruise down the highway it stays cool until I get back into town and running at lower speeds it starts to overheat. Normally after driving at highway speeds for 15 minutes I lose about 1/4 gal of coolant. Any ideas as to where it's going and why it's overheating?

 

If you don`t have any leaks at any of the radiator or heater hoses, then i would guess that you have a bad head gasket.

 

Likely coolant is being forced out of the cooling system while on the highway (due to engine compression leaking into the cooling system). Then when you get back to town, the lowered coolant level leads to the overheating you see. Some tests to try are to have a pressure test done on the cooling system (look for a pressure rise with engine RPM increase). Or a chemical test on the coolant to see if there is exhaust gas contamination:
- http://www.arrowheadradiator.com/hea..._leak_test.htm

 

Take the spark plugs out. If one has broken ceramic, that's a sign of water. Also, shoot some air into each spark plug hole, you should see some water splash out of one. The headgasket can blow and allow water to go out the exhaust and not in the oil.