Need some help please. 2006 Mazda RX8 automatic. Radiator was leaking badly. Replaced it. All is well. Holding fluid. Now, all of a sudden radiator cap light goes on after running awhile. Then the fan will run for a minute or two after shutting off. Changed the cap. Same thing. The tank is plastic and I am wondering if it could be the seal around the edges of the plastic tank. It looks ok, nothing obvious but maybe it’s slightly warped or something. Any help would be appreaciated. Thanks.

 

There is no cap light, but there is a low coolant light, and with time it can go bad and light up for no good reason. That's fairly common.

Check for signs of a coolant leak, the tanks can crack. But if it's not damaged and thr coolant level is not low, then it's probably jist the sensor. You can replace the whole bottle + sensor for $150ish

 

Ok...this is my wife’s car. So, it is the Engine level coolant warning light. She told me the radiator cap light....😎 ok......so everything is dry. I was thinking of maybe it’s the plastic resivor tank, since it’s plastic maybe when I put the cap on it’s not a good seal?
Or it’s the sensor that plugs into the resivor tank like you said. The only thing is that she said the fan will run after driving a long distance when the car is shut off. I asked her how many times it happened and she said once. So.......I gave her some homework notes to take over the next week!
Like when the light goes on, does the fan actually run when shutting off the engine. 😳😂I have a feeling it’s that sensor. Let’s see. I will be back when I uncover a little more.
This car is a pain in the ***!

 

The fan stays on after you shut the car off if the engine is above a certain temp. It doesn't mean anything is wrong, just that it is a hot day or you were driving the car hard before shutting it down. Mine does it pretty frequently when just driving normally here in Florida.


The coolant sensor in the tank is known to go bad. You can find a new tank for around $100. I just replaced mine earlier this month. You can just ignore it, or unplug the sensor to disable the dash light. However, if you do end up losing coolant on a drive you won't know it until your engine is overheating.

 

Is your coolant level actually low? If it's hard to see, shine a flashlight on the top of the tank and you will be able to see the level. The level should be between H and L mark on the side of the tank when it's stone cold and on a flat surface.

The sensor can go bad. Like said, you could replace the tank. Note that when you change out the tank, there is a hose that connects the bottom of the tank and the top of the radiator. Cut that hose down the middle and carefully remove it in pieces. If you yank it, you might end up breaking the top of the radiator and that turns into a costly repair. Some sellers like Mazmart includes the said hose with the bottle, but if it's not included, buy it.