First, thermostats do not cool engines down. They are designed to help the engine get hot to a certain point, then the water pump and radiator cools the engine.
The fist thing to check is the radiator cap/surge tank cap. Remove it and look to see if the black rubber gasket is intact and not clogged with dirt. Next start the engine and let it reach operating temp. (This is when the thermostat opens) There should be pressure in the hoses. If no pressure is building, then the radiator cap/surge tank cap is leaking.
Then you can check to see if the water pump is working by squeezing the upper radiator hose while someone revs the motor up and down. If you feel the pressure in the hose, then your pump is ok.
You can check your thermostat by feeling both the upper and lower radiator hose after the engine runs for about 10 minutes. (After the thermostat opens)
If the upper hose is hot and the lower isn't, then the thermostat is stuck closed.
Also, if you've added coolant after a loss, then you could have air in the system. You can bleed this air by removing the radiator cap and allowing the engine to heat and cool a couple times. (You need to set the heater on high) Also, with the radiator cap on but the surge tank cap off, squeeze the upper radiator hose a couple times while the engine is running.
Next, are you cooling fans coming on? At idle after the thermostat opens, the fans should come on. If not, check the relays. If the relays are good and the fans are getting power but not turning on, the the fans are bad.
Finally, if none of this works, either you have a blockage in the system, or a blown head/intake gasket.
You can easily check a blown gasket by first looking in the oil. If it's milky white, the gasket is blown. If not, open the surge tank cap and start the engine. While someone revs the motor, look inside the surge tank. If you see large bubbles (Not foamy bubbles), then you head gasket is blown and it's allowing hot exhaust gas to build up in the system.
Saturday, September 18th, 2010 AT 6:49 AM