I have a '74 RX-3 that I replaced the coolant temp sending unit with one of a newer engine, I think is a 2nd gen or so. The problem I'm having is that the gauge is reading all the time almost at the "H" side of the gauge, but I know it is around 185-190, according to the mechanical autometer gauge I also have. I will like to get the factory one to read normal at least, but haven't been able to find a replacement temp sensor. Does anyone knows where can I get one or if there is someway to calibrate the sending unit with the gauge, like installing some sort of resistance or such???

 

yeah the older gauges don't play well with the newer sensors

 

I was able to get one from Autozone. the connector isn't the same as the stock one so I had to make a new one out of those connectors you can buy. It works perfectly fine.

 

you have to match the sender to the dash year
.. the rotary ones are the funny 1/8 BSPF 28 thread and usually a bullet head .. though i have seen a few spade type ones
back then im thinking you need one with the green ID ring .. but may be on the cusp of the black one

i am sure you will find one if you look hard enough .. myself have a private collection bucket of s/h ones ( not for sale )

the big help is that the piston models copped the same output range for the same years.. and quite often are still avail
...but use a larger thread size

and on the pre r5 blocks ( and post 86 blocks ) , can be fitted with a little mucking about into a location down on the front plate dizzy side
( there is a bung there on most pre R5 plates )

 

Thanks for the help guys. RX2fan, do you happen to know or remember the part number or application of the one you got? I will like to get one to fix this thing, even tho I'm thinking of getting rid of it, it's getting old and tired of fixing something and something else shows up.......

 

Temperature Switch | 1973 Mazda RX2 1.1L 4BL Rotary | AutoZone.com

I believe this was it

 

Thanks guys for all the reply's. Still looking for this unit, my local autozone has been of no help so far, but the hunt continues....

 

when i search i keep finding a tridon branded sensor ... m8 x 0.75 with an NTC curve
( post 86 engines use the 1/8 BSPF 28 thread )

however it claims to suit 1970 - 1985.. and in my experience,, this is not quite true
( as in my experience there is a m8 x0.75 green sender,, and one in black..
and the black one seems to suit the 1981-85 dash
.. while early cars will read 3/4 on the dash with this one and like the green top senders instead )

ac delco and BWD seem to come up with an image of a black topped sensor

other listings seem to confirm the black starts in 77 in GLC and 1981 in rx7

i also find a listing for an FAE Temperature Sender 32170
.. and it is the correct thread, and green top like i expect

i would err there

ps .. there is also TS67 ( SMP brand ) that is the larger piston type thread
( for relocating into water pump or front plate as i hinted above )
that also corresponds with some mazda/ ford dashes down to 73

 

also tridon TTS006. same large 4cyl thread ( m16 ? x 1.5 )
but for 808 dash, 1973

and

1973 Mazda 808 Engine Coolant Temperature Sensor AC Delco ACE8038 ( m16 x 1.5 )
needs to be adapted in somewhere and should work

ACE8039 is the m8 x 075 version


also ( fuel miser? )
CTS112-21 ( the large and coarse thread )

and

CTS111 ( the small and fine thread )

 

these look a little better, as they dont seem to cross link to cars with any post 81 dashes

( small thread ) .. and specified as 1975 rx4 and rx5 part

1757-18-510A



echlin TS6041
FAE 32140
ACDelco 213-1108
WELLS TU71
BWD WT512
GM 19107014

 

Still looking, all the ones I have been able to find seems to be the ones that bolt at the water pump housing, I need the one that goes in the engine block, right under the oil filter pedestal....

 

the numbers i put up last are all m8 x 075.. the fine thread on early blocks

however .. if you have a certain early block front plate
( look at front plate down low on the spark side valley )

and there ( on many early,, and late blocks ,, but not on some r5 plates )
should be a m16 x1.5 blind bung into the water jacket

this is in a final pass location.. and is a very accurate spot to put in the large 808 sender