Coolant Light On But Tank Is Full – Solutions & Causes!

Facing unusual activity like coolant light on but tank is full when driving might give an off feel. The first thing you have to think of is repair. But sometimes it's too costly to hire an expert and solve the error in the coolant light.

And, that's how you are stuck in this guide to get an alternative solution, something that includes self-help? Don't worry! This guide will lead you to 5 repair methods to the major issues. Hope It Helps.

Coolant Light On But Tank Is Full ”“ Solutions & Causes!

Coolant Light on But Tank Is Full ”“ Fix the Issue!

The coolant light-on when the tank is filled can happen due to errors in coolant-related parts or modules. Just replace the faulty parts and cure other issues using the proper methods.

Usually, the coolant light comes on when car starts which is called Blub Check procedure. It's to see whether the headlights are functioning properly or not. However, if the signal stays on till the engine starts, it indicates an issue.  

coolant light comes on when car starts

You can check how to fix coolant mixing with engine oil as sometimes this thing causes this kind of error. However, in most cases the coolant light turns on can happen due to reasons such as: 

  • Bad coolant sensor.
  • Overheat.
  • Cracked head gasket or engine block.
  • Bad coolant level module. 
  • The air inside the cooling system.

I have given solutions in steps-by-step based on causes serially. So, based on these issues, find out your perfect solution and then solve it. Wait! Be sure to grab tools before you start the procedure.

My Recommendations

  • To patch up cracks in the engine block or head gasket, the K&W 401224 FiberLock is my favorite. It is rigid in formulation to use in metal items for repair. And, you only need to pour it over the cracked surface.
  • As a reliable coolant bleed screw, the URO Parts 17111712788 is the best in both worlds. It comes with an O-ring while being super solid to ensure no air slipping inside the cooling system.

1. Faulty Coolant Sensor 

If your coolant light on but not overheating, it signals the sensor issue. Now, this kind of hitch meets when the sensor itself needs replacement or due to a bad wire.  

  1. Replace bad coolant sensor:
  2. Take out the negative terminal of the battery and then the positive one. Be sure the car hasn't been used in several hours.
  3. Remove the plastic cover of the engine and then plastic air intake tubing (if your engine has).
  4. Find the coolant sensor. Next, drain the cooling system and detach any electrical parts connected to the sensor. To do it faster, use a ratchet wrench like WORKPRO 8-piece Ratcheting Wrench Set.
  5. Pull out the coolant sensor. And insert the new one.
  6. Attach everything back to its place.
  7. Replace bad wire of sensor:
  8. In most cars, the wire would be pink and the location is on the rear-side of the engine.
  9. So, locate the wire and then see if it is loosely fitted or needs replacement. Detach the wire and insert a new one.

Warning: Changing the wire of the coolant light is a bit risky so I suggest seeking help from an expert.

2. Overheat Issue

The red coolant light pops up on the dashboard in the winter or summer when the engine is overheated. It means the coolant is fine and working but can't circulate to cool down the system. To fix it,

  • Connect the radiator plug tightly to the car. 
  • Next, replace the radiator hoses if it has pinches. 
  • After that, check the thermostat whether it's good or not. If not, then change the part only. 

3. Broken Block or Gasket 

Sometimes due to lack of lubrication and maintenance, the engine goes through major issues which result in cracks in the block and gasket. And when these things happen, it causes the coolant light to keep on even if the tank is filled.

Repair the crack of block or gasket:

  • Use a strong repair spray to conceal the cracks of the engine block or gasket. And wait for 20 minutes or more to ensure no leak. 
  • Drive the car for some minutes and then check if the block or head gasket is fine or not.

4. Faulty Coolant Level Module

Another reason why the coolant light stays on when the tank is full can be due to a bad coolant level module. To fix the issue, refill your coolant in the max meaning ”˜full' when the engine isn't hot at all. Then, apply 50/50 coolant and water mix.

Pro Tip: As an alternative option, using the best oil for Ford F150 or other truck (based on your car) engine might solve the error.

5. Air Inside Cooling System

After the full tank, if the coolant shows no heat at all, it means air enters the system. It will damage the entire cooling system if not taken action. The issue can be solved using the vacuum system.   

  • Attach jack under the car which can lift 1” to 2” on the front more than rear side.
  • Use a bleeder screw to open the coolant slightly so that air goes out of the bleed.
  • Fit filler cap loosely and adjust heat and fan speed to the ”œMax” level.
  • Next, start the engine and idle it for several minutes. Be sure the car is warming up to the right temperature (operating).
  • When the temperature rises, warm the engine in between 2,000 to 2,500 for a few trials. Insert all parts back to the place and test drive for a few minutes to see if air enters the cooling system or not.

Ending Notes

Even if you frequently clean or care for the car components, still the coolant light on but tank is full issue can occur. So, no need to think negatively about it. Instead, try out the given steps based on the trouble type to treat any fault immediately. You'll Do Great!

About Jeremy

Hello! My name is Jeremy Bloomberg. I have been passionate about carpentry and DIY. Over the years, my passion slowly turned into expertise and wider knowledge about electronics. I’ve been involved in numerous projects, both professional and personal. I want to share all I have learned with you. Welcome!

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