I replaced my radiator this weekend with a Koyo. Also installed a Miata thermoswitch (what a bitch by the way). Now, I got home from work today, turned off my car and the fans stayed on. So I let it be, and they stayed on for maybe 10 min. I guess I should be happy they are doing that without having done the fan mod, but I want to make sure that it is not a sign of a short, or some problem.

 

It means your car has had the "fan motor update" done, which basically runs the fans for 10 minutes after shutdown when the coolant temps reach a certain level. Nothing to worry about.

 

That ^^ sounds reasonable.
But also, the fan mod is a simple grounding of a loose wire to complete a curcuit. In other words, this loose wire down in the kick panel may now be contacting metal.

Raj

 

Kento, thanks. But now I am concerned as they have never done that before. Am I to assume that now my coolant is hotter after driving home than it used to be with the stock radiator? Or does it use the thermoswitch to determine this "fan motor update" that you speak of. If so, then, it would be using my new Miata thermoswitch and turning them on at a lower temp.

 

If I'm not mistaken, the Miata thermoswitch activates (tells the ECU that a certain coolant temp has been reached, which causes the ECU to activate the fans) at a lower temperature, thus your "10-minute fan sequence" is triggered, even though you've never encountered it before.

 

If your fans are staying on all the time when you shut down the car, that could have an adverse effect on your battery. With the "fan mod" you wait 30 seconds after the engine shuts down, then turn off the switch to put the fans on medium speed. If you leave the switch on, the fans stay on high for ten minutes before shutting down. The problem occurs when leaving the fans on high. The switch stays "on", and it drains your battery. After 2 days, you will have a dead or very weak battery. I hope you do not have this problem.

 

No, like I said, they turn off after like 10 min or so.

 

I would be concerned. Do you have a temp gauge? The only time my fans ever kicked on after shutting the car off (with the stock ecu) was after two drag strip runs in a row in 95+F heat (and sitting for 15 minutes inbetween). My coolant temps were probably over 230F at shutdown (didn't have a water temp gauge back then).

I would make sure you properly burped the system and everything is ok.

 

I've never had my fans stay on for 10 minutes after complete shutdown and I have the Miata thermoswitch. They still only ever come on if the temps are high and the key is turned to IGN or maybe ACC I don't remember.

 

What method of "Properly burping the system" do you suggest? I still have AST and I just filled and topped off 3 times or so.

 

Just get your hands on every coolant tube you can find and squeeze it a lot. Then shake the engine if you can.

 

IIRC the fan thermoswitch is essentially a "dumb" switch that immediately puts the fans in high speed mode. The ECU doesn't monitor it other than allowing the fans to come on, so changing back and forth from the Miata and stock switch will have no effect on the fans running after shutdown.

There are three coolant temp sensors: One in the block runs the gauge, the thermoswitch at the top rear of the coolant neck that turns fans on high and the thermosensor just under the coolant thermoswitch. This sensor is the one the ecu gets its coolant temp from and uses to trigger low and medium speeds along with determining engine warmup etc.

 

Then I was mistaken...

Thanx, Damon.

 

I think you have the 2 switches mixed up. The one that goes to the ECU (the sensor) is on top. The "dumb" switch that turns the fans on, is on the bottom. That is the one that is replaced with the Miata switch. So does any of this explain why my fans stay on when the car is off? And keep in mind, the fans just SA=TAY on, they don't COME on. If they are already on, ie if the car was idling for a while before shut off, they stay on for 10 min (haven't timed exactly). If the fans are not on when I turn off the car, ie just got off the highway and the car is nice and cool, they do not come on.

 

Sorry if I got the top and bottom sensors on the back of the coolant neck mixed up; it's been a while.

Your fans function exactly as they are supposed to due to the update Kento mentioned. If the coolant temp is above a certain point when the car is shutdown the ecu will run the fans for 10 minutes or until the temp drops back down below the cutoff point. If the temp was not above the certain point the fans will not run after shutdown.

My car will run the fans occasionally after shutdown during the summer months.

 

And you don't have the Miata switch, right Damon?

So wait Damon, are you sure that with the "Fan Update" that it is the ECU that makes the fans stay on, and not the actual thermoswitch?? Because if it is the thermoswitch, then it makes sense that they would stay on now and did not do that before, since now the thermoswitch, turns them on at a lower temp. But if it is actually the ECU that turns it on, then something is wrong, since that means that my temps are much higher than they were before the radiator upgrade, since they never came on like this before.

 

To get the air out of the cooling system, follow this procedure:

Place a jack under the left front of the car at your normal jacking spot. Raise the car about 3-4 inches. It does not have to come off the ground. Disconnect the throttle body coolant line at the throttle body. This will allow air to escape thru the throttle body, which is the highest point in the system. Remove both filler caps. Fill the ast. Keep an eye on the TB coolant line. When/if coolant starts coming out, re-connect it. Give the ast a moment to go down, and continue filling until the level no longer drops. Replace the ast cap, and fill at the filler neck.

Make sure you have re-connected the TB coolant line. Cap the filler neck.

This should get nearly all the air out of the system. Drive it, let it get fully warmed up, and shut it down. After it cools of completely, remove the caps and check the levels. You will probably have to add a tiny bit.

Check again after another short drive or two.

 

The miata switch turns on the fans at around 212. If you shut down the car, and the coolant temps are over that, the fans will stay on until it drops. Thats the same way it was before, except now they come on at a lower temp. It sounds like things are working as they should.

 

No, I do have the Miata thermoswitch.

Yes. Fan speed and actuation is ALWAYS done by the ecu. The thermoswitch's only function is to tell the ecu when to go to high speed. Essentially the thermoswitch will override everything the ecu thinks about coolant temp and make the ecu kick the fans to high. The ecu is in control of the fan speed relays, but when told by the thermoswitch that it's time to put the fans to the high setting the ecu will obey in every circumstance. Swapping to the Miata thermoswitch does not effect the car in any way other than making high fan speed come on earlier. It does not effect the ecu's thinking in any other way.


I assume you don't have a real water temp gauge? Your fans are working as they are supposed to. The only way to see your temps to prove it is to have a gauge though.

What coolant mix is in the car? Did you change the water/coolant ratio when you swapped the radiator? The higher the percentage of water, the cooler the car will run.

 

Damon, is there any way to get the update? I might be confused but you are talking about a reflash of the ECU or something to that extent are you not?

 

It was a recall performed by Mazda. Remove the passenger kick panel and look at the ecu. If there is a black box about the size of a pack of cigarettes in there your car has had the fan update performed. The ecu itself is unchanged.

 

I guess it would be pretty obvious, so it's definitely not there. And seeing as it's a recall, I guess it's time to call the local Mazda for an appointment

 

Ok, sounds good Damon. No, I don't have a real temp gauge. As for the mixture, my mixture was 50/50. When I did the radiator swap, I only put water back in. So the only antifreeze is the amount of 50/50 that was in the block and did not get drained.

On a side note, my stock temp gauge always reads just a hair above the middle. And that is before my radiator/thermalswitch/thermostat swap and after. Does it sound right that it would read just barely above the 9 o'clock position, or should it be dead at 9? Keep in mind, my car only has 30k miles on it and there is nothing wrong with it.

 

The stock gauge is a POS. It will read the same from around 120 degrees to about 240. You should linearize it, or get an aftermarket gauge.

 

I have head some people's was actually behind the ecu. Remove the ecu from its bracket to be certain.