my 1993 toyota four runner runs great. my only problem is the temperature gauge stays about in the middle almost all the time with the exception of when i go up a reasonably steep incline. the engine then heats up to the red in less than an 1/4 of a mile. as i crest the hill and start down the hill it cools reaasonably quick as long as i keep the idle up. the radiator is brand new and the coolant is not leaking out. it only overheats when going up an incline. thanks to all.
What was the reason for the radiator replacement?
Do you have AC? When the rad was replaced was the front and grill checked and clean for debris, fluff, etc? IE) Infront of the AC Condenser.
Did you check to see if there is oil in your coolant, or coolant in your oil.
A leak down test is much better than a compression test. A leak down test will let you know if your headgasket is leaking by pressurizing the system with compressed air. It will also let you know how much you are loosing in pressure, etc. It is possible you may have the beginings of a headgasket leak.
It is possible, but not likely that the thermostat is the issue. If they go, they normally break in the stuck open position.
Did you replace your rad cap when you replaced the radiator? Did you burp/bleed the system for air?