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Old 2-17-05, 15:27   #1 (permalink)
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Water Thermo Switch (on radiator)

Ok, I'm changing out my radiator in my LX and I tried to remove the connectors for the Water Thermo Switch (on the radiator down by the Lower Coolant Hose) when the connectors disintegrated and snapped one of the male ends on the switch off. Now I called around and it sounds like it's a dealer only item. I called Mazda and they wanted $55 for a new one! Looks like I'll be headed for the junkyard tomorrow. Now my question is is what is the function of this Water Thermo Switch? Is it safe to drive around with it disconnected? Any help would be greatly appreciated..

EDIT: I should have searched before I posted this thread. Sorry.

Last edited by cenatix; 2-17-05 at 15:34..

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Old 2-17-05, 15:39   #2 (permalink)
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i could have lost my mind. but i didn't have any electrical connectors on my radiator when i removed mine.

Please Note: The above statement is in no way the advice or comment of a professional, just an idiot working on a car in the driveway.

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Old 2-17-05, 15:41   #3 (permalink)
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I'm just guessing, but maybe it tells the fan when to kick on? Or would that one be loacated on the t-stat housing, along with the fan connector? Then again, maybe it's for the gauge? I don't know for sure, just throwing out ideas.

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Old 2-17-05, 16:24   #4 (permalink)
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Quote:
Originally Posted by Guy2626c
i could have lost my mind. but i didn't have any electrical connectors on my radiator when i removed mine.
As far as the PGT goes, the sensor is there on the 89's, but not on the 90's.

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Old 2-17-05, 16:37   #5 (permalink)
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Only the 88-89s have this switch in the radiator. 90-92s have a significantly different cooling fan setup.

I believe that switch is one of the switches turns on the cooling fan - let me check the 88 training manual when I get home.

EDIT: My hunch was wrong; this thermoswitch does NOT turn on the cooling fan; rather it is an input to the ECU. See my post below.

Last edited by magik8; 2-17-05 at 18:48..
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Old 2-17-05, 16:50   #6 (permalink)
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I thought the switch to turn on the cooling fan was on the thermostat housing. I did a search and magik, you stated that it sends information to the ECU. Maybe I read it wrong?

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Old 2-17-05, 17:07   #7 (permalink)
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My 89 GT has a thermo sensor at the bottom back of the radiator on the passenger side. (pointing towards the block) When one of the connectors broke off mine a couple years ago, NAPA had the part. I recall it being $15 or less. $55 is a price that earns the designation "Stealership."

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Old 2-17-05, 17:27   #8 (permalink)
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Check out this NAPA link - or search on item MPETS5520SB - cost is 21.99. I think this is the one, but it looks like the 2 contact prongs have a plastic shield over them.

http://www.napaonline.com/cgi-bin/nc...grpid=86834201

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Old 2-17-05, 18:35   #9 (permalink)
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I had the same concern on my '89 LX when I put a used '90 626 radiator in. The hole for the sensor wasnt there. So i left it unplugged. I never saw a difference in 3 years. No clue what it does.

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Old 2-17-05, 18:39   #10 (permalink)
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OK, enough guessing. Let me set this straight for the 88-89 cars (90-92 cars are completely different).

First off, there are two thermoswitches in the thermostat housing. These are for turning the radiator fan on/off. One switch closes when the coolant temp is over 97 C (177 F), and the other closes when the coolant temp is over 108C (226 F). Switch #1 will only turn on the front main fan (white blades). Switch #2 will turn on both the front main fan, AND the a/c condenser fan. On ATX cars, when Switch #1 is on, the main fan spins at a lower speed than if Switch #2 is on, in this case both fans will be on full blast. On MTX cars the main fan has only one speed.

The third thermoswitch (that's right, there are three of them on the 88-89s) is located in the bottom of the radiator. It turns on when the coolant temperature reaches 17 C (62.6 F). This switch has nothing to do with the cooling fan, rather, it is an input to the ECU - I'm guessing it's used for fuel mixture or idle calculations - it's hard to say as the manual doesn't spell out exactly what it's for besides an input to the ECU.

Again, the above is only valid for 88-89 cars. One thing to note here is to make sure you get the right thermoswtich as they do not all close at the same temperature!! If you're buying from NAPA, make sure you get the right temperature thermoswitch!

Last edited by magik8; 2-17-05 at 18:44..
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Old 2-17-05, 18:43   #11 (permalink)
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Quote:
Originally Posted by mlp-mx6
Check out this NAPA link - or search on item MPETS5520SB - cost is 21.99. I think this is the one, but it looks like the 2 contact prongs have a plastic shield over them.

http://www.napaonline.com/cgi-bin/nc...grpid=86834201
Please note that this is appears to be a sensor and not a switch. This is an important distinction. In addition to the switches I described above, there are two thermosensors located near the distributor; these are variable resistors that change with temperature, completely different from a switch. One thermosensor is for the temp gauge in the dash, the other's an input to the ECU.
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Old 2-17-05, 18:52   #12 (permalink)
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Quote:
Originally Posted by magik8
Please note that this is appears to be a sensor and not a switch. This is an important distinction. In addition to the switches I described above, there are two thermosensors located near the distributor; these are variable resistors that change with temperature, completely different from a switch. One thermosensor is for the temp gauge in the dash, the other's an input to the ECU.
You are correct. Perhaps this is the one. Part # MPEFS207SB for $21.99. This looks more like what I replaced. NAPA calls it a Coolant Fan Switch.

http://www.napaonline.com/cgi-bin/nc...grpid=86834231

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Old 2-17-05, 18:53   #13 (permalink)
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Quote:
Originally Posted by magik8
One thermosensor is for the temp gauge in the dash, the other's an input to the ECU.
I always wondered why they used 2 sensors when it would seem that one could do just fine...

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Old 2-17-05, 18:58   #14 (permalink)
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Quote:
NAPA calls it a Coolant Fan Switch.
What I'm a bit concerned about is that the website doesn't list what temperature it actually opens/closes at. This is important as the three switches aren't the same in this respect.

Quote:
Originally Posted by mlp-mx6
I always wondered why they used 2 sensors when it would seem that one could do just fine...
Perhaps one has a voltage/current/resistance range more suitable for running a gauge (that's not all that accurate or precise), and the other is more precise for ECU calculations? Just a guess.

Last edited by magik8; 2-17-05 at 19:08..
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Old 2-17-05, 20:17   #15 (permalink)
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I was of the belief that the sensor on the bottom of the rad turned the 2nd fan (the one that comes on with the A/C) off when coolant temp was below spec.

I'm more likely to beleive magic than myself though.

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