95 Corolla overheats, probable coolant leak or maybe thermostat, need more advice.

Question

Vehicle is a '95 Toyota Corolla.

Was driving yesterday for about 5 minutes and glanced at the temperature gauge which I noticed was running pretty high (weather has been around 90 degrees f lately). As I was watching it pushed into the red so I immediately pulled over and turned off the car.

Opened the hood, no steam or smoke which I assume is good, but looked at my coolant tank and saw that it was bone dry. Left the car overnight and came back in the morning with more coolant, filled it to the fill line and drove home, about 1 mile, and everything seemed to be alright.

Today I wanted to test it some more so I checked the coolant and seeing that it was still at the fill line I drove about 4 miles and it started overheating again, so I pull over and turn off the car immediately.

I check the tank again and the coolant is still at the fill line. I walk away to call a friend for a ride and look at it again 2 minutes later and the level of coolant has dropped to about a quarter, and a small, fresh puddle is visible underneath the car.

My conclusion is that it was obviously a leak, but a buddy says it might be my thermostat acting up, because of the odd behavior of the coolant.

I wanted to get a second opinion so please let me know if you need any other info. Some additional things that might be helpful are I didn't see any coolant in the oil when I checked, and I also didn't open the radiator cap to check for coolant since the car was hot, but I will check that soonish.

Answer 1

What you're referring to as a "coolant tank" is your radiator overflow tank. While it does have to have some coolant in it, putting coolant/water in it doesn't do anything to cool your engine really. You need to twist the radiator cap off (make sure you wait for it to cool off) and pour coolant or maybe for the time being while testing, just tap water.

There can be several reasons why your engine may be overheating, in the order of repair complexity:

1. Radiator cap lost its gasket and it is letting steam out, draining the system
2. Coolant system leak somewhere (hoses or clamped connections). This can be tested using a pressure test kit.
3. Thermostat is stuck closed
4. Water pump is not spinning the impeller (not passing torque from the drivebelt pulley)
5. Head gasket(s) are blown.

A common way to test whether that's the case is to use combustion leak detector to chemically probe your coolant fumes for oil and other impurities that get into it through gasket leaks.