Hey all, I just bought my first fc and I'm loving it. I'm trying to get the stock coolant gauge working and I can't seem to find the right sensor. I found the yellow wire and when I connect it to the sensor under the oil filter nothing happens. I grounded out the wire and it'll peg the needle so the gauge n wiring should be okay. I ordered one ssensor and it came with a connector for 2 wires. Another sensor came with one, but was way too large like the first. Also what's the sensor on the coolant filler neck? Thanks again, I really want the gauge connected before i install my koyo rad + thermostat.

 

can you post photos of these sensors you mentioned? of the two sender units below the oil filter area, the temperature is the smaller one.

if you're referring to the sensor on the back of the water pump, then I think that's the one that interacts with the ECU.

 

one under the oil filter is what you need .. s5 blocks use a different sender and a larger thread,, so you cant swap it out for something you need

two wires is for back of water pump for the ecu.. the other is a thermoswitch for some cars with aux fan

if you have the s4/5 missmatch issue ...take off the PS bracket .. on the front plate down low is a 3/8 npt bung .. take it out and tap into it your s4 sender

 

If I had an s5 block is think it would be okay since it seems like they keep sending me the larger sensor. I'm dieing to install my koyo but am afraid of getting an air pocket and not knowing about it. Thanks for the help guys.

 

86-92 Engine Electrical
Think i found it. I think its the 81-88 old style w crush washer. Sucks i wanted to do everything today, looks like ill have to wait. Anyone know any Chicagoland rx7 parts stores?

 

Found one for a 12a from advanced auto parts for $20.thanks again

 

The 81+ FB and Early S4 cars use the sender w/crush washer you needed. For some reason, Mazda chose to use a weird thread pitch on this, M8x0.75. Partway through I believe 1987 is when they changed to the 1/8" NPT version with the same bullet connector. Not exactly sure when the change was made, but my 87 GXL (built on 11/11/86) had the same M8x0.75 sender that your car has.

S5 & FDs use a 1/8" NPT gauge sender with a 0.250" quick disconnect type connector here.

The two-wire sensor is the Coolant Temperature Sensor, mounted on the rear of the water pump housing. Thread pitch is M12x1.5. It feeds temperature information to the ECU. On top of the water pump housing filler neck is the A/C Fan Thermoswitch that uses one 0.250" Quick Disconnect type connector. This is M16x1.5 and breaks continuity at 195 degrees (207 for S4 TIIs). S5 cars use a M16x1.5 thermoswitch that behaves normally, turning on at 207. FDs use a higher temperature version of the S5 switch sharing its connector as well.

Connectors for the S5/FD fan thermoswitches seem to be difficult to find due to desirability AFAIK. If/when I find out who the manufacturer is along with a part number, it will be added to the Second Generation FAQ.