Q: Over heating but water is flowing through radiator

Hi there, there are a number of things that can cause a vehicle to overheat. The water flowing through the radiator can be a little misleading. Here is a list of possible causes:

• Thermostat
• Water pump
• Clogged radiator. Inside and outside.
• Head gasket
• Low coolant level
• Radiator cooling fan

These can cause overheating and as you pointed out, the gauge or the temperature sensor could be reading incorrect. An infrared temperature gun is the best way to determine if your car is actually overheating. These can be purchased at your local auto parts store. An infrared gun is often around $50 and isn’t always necessary, but it can help clarify if your motor is actually overheating.

Checking the coolant level should be done with the car cold by removing the radiator cap and making sure the radiator is completely full. Then top of the coolant jug if it is low.

Testing the thermostat is fairly simple. Begin with a cold motor, start the car and wait for the upper radiator hose to become hot to the touch. If your temperature gauge is showing your car is overheating but the upper radiator hose isn’t to hot to touch, you need a thermostat.

Radiators can clog internally and externally. External clogged radiators will have road debris stuck in their cooling fins. This you can see by simply visually inspecting the radiator from the front of the car. You can clean it with a water hose usually. Sometimes you will need to use a soft brush. Be sure not to bend the cooling fins. This will also result in overheating. Internal clogging requires the car to be completely warm with the thermostat open. Drive the car around the block and come to a stop in your driveway, turn the car off, open the hood and feel the radiator with your hand. The top should be to hot to touch and the bottom should be cooler. You are checking for cold spots that will be cold to the touch. If you find cold spots, you need a new radiator.

The best way to check for coolant flow is to remove a heater hose, then start the car. If the water pump is working, coolant should shoot out of the hose. Often choosing what hose to remove for this test can be challenging. So if the first one you remove doesn’t yield any flow, try another, but don’t remove the radiator hoses. If you don’t get flow, I would suspect the water pump impeller has problems.

Checking for a blown head gasket can be a challenge if you have never done it. The ideal method is using a tool called five gas analyzer. The next method is what is called a block tester system. The gas analyzer is a very expensive machine. The block tester can be purchased at your local auto parts store. Simply follow the instructions. The challenge of testing for a blown head gasket is because it happens in degrees. It can be really bad, it can happen only at certain times and it can happen randomly and inconsistently. This is where experience comes into play.

If you should need help with determining if you have a head gasket problem, I recommend the having a certified technician from YourMechanic assist with diagnosis of the overheating issue in order to have this properly corrected.