if i understand correctly the oil preasure sender thread is 1/8th BSPT, and the coolant temp sender for the gauge is also 1/8th BSPT.

my problem is, i built a motor and i bought all the irons used off rx7club, they are all s4 tii irons, they did not come with an oil preasure sender or temp sender. i have my old oil preasure sender off my N/A s5 engine, but for the life of me i couldnt get it to thread in, i pulled the oil preasure sensor off my other rx7 (88 N/A) and tried to thread that one, no luck. its like both my oil preasure snders are to large they wont begin to bite or anything, 1/8th NPT wont fit, and none of my random array of bolts will fit either. this is sewriously stumping me, how can an OEM oil preasure sender not fit in an OEM s4tii iron.. especially since its too small, it would make sense if it was too big i would just assume someone drilled and/or tapped it..but too small sounds like...sounds impossible, i checked mazdatrix and they only sell one oil preasure sender and its fits all 81-92, so im assuming turbo and N/A oil preasure senders are the same. any help would be greatly appreciated.

 

it is BPT not NPT thread.
why they don't fit I am not sure.Is the hole you are trying for oil or water?( they are close to each other).maybe wrong hole?..

 

No it's the right hole, i can clearly see both holes.(I removed anything obstructing my view) maybe someone sold me an FD iron or something, do they have a different thread for the oil preasure sender in FD?

 

nothin...i dont know what else to do, i ordered a 1/8th BSPT plug and a 1/8th BSPP plug and im gonna see if those will work. (i dont need the oem preasure sender i just need that hole plugged!!)

 

Your rear iron has to be modified, All FC and later rotaries use the same 1/8" BSPT thread pitch for the Oil Pressure Gauge Sender. On the 20B FC, I'm using a stock S4NA oil pressure gauge sender and it threaded in just fine after removing the plug that the previous owner put in. FWIW, all S2-S5 rotaries use the same oil pressure sender.

Some guys use a FD's sender as there is a calibration guide for it somewhere in the Haltech section so the Haltech can see oil pressure without purchasing the commonly used GM sensor. Can't recall who made the chart or the values for it, but it is there somewhere.

As for the Coolant Temperature Gauge Sender:
Early S4's use a M8x0.75 threads with a bullet terminal. Late S4 switched to a 1/8" NPT thread pitch while keeping the bullet terminal. S5's, JC Cosmo engines and the FD all use 1/8" NPT with a 0.250" Quick Disconnect terminal. These can be found on first generation Miatas as well. My car was an Early S4 (built on 11/11/1986), so I couldn't reuse its sender in the 20B.

 

a tapered /8 npt thread will go in and seal just fine. using aftermarket sensors in both holes and they dont leak a drop

 

Some 2nd gen water temp sensors are straight thread and use a crush washer. Pretty sure all the oil sensors are 1/8 BSP. There are BSP to NPT adapters available for those that want to install an alternate sender.