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Q: My temperature will rise to hot then come back down hot comeback down in doing so the fan will come on really hard vibrating

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My tempratur in my jeep will rise to hot then slowly fall rise to hot fan will kick on running strong like vehicle is overreving kinda rise in the red and drop

My car has 210000 miles.
My car has an automatic transmission.

A: Hi there. There are a number of things that...

Hi there. There are a number of things that can cause a vehicle to overheat. I suspect you have a low cooling system, but the following are the steps you should follow to accurately diagnose your cooling overheating issue. You should check these items:

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

Coolant level

The first thing to do is check the coolant level. It should be done with the car cold by removing the radiator cap and making sure the radiator is completely full. Top of the coolant jug if it is low.

Thermostat

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.

Radiator

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. Usually you can clean it with a water hose. Sometimes you will need to use a soft brush. Be sure not to bend the cooling fins. Checking for 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 hot to the 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.

Water pump and coolant flow

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.

Head gasket

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 can be really bad or just have a slight failure. 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.

Fan or fans

It is good that your cooling fan is working. All spinning objects will exhibit some level of vibration. Knowing how much is normal is a factor of experience. Either way, the fan should be pulling air through the radiator. You can feel this by placing your hand in the path of the air flow. It should be significant. Be very careful not to get your hand stuck in the fan blades while it is spinning.

If you should need help determining if you have a head gasket problem, I recommend having a certified mechanic diagnose the overheating issue so that this can be corrected.

Good luck!

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