The only hiccup I have had in this build so far has been the temp sender on the rear iron is broken, and the head came off while trying to take it out. It is hollow, and I now have one of my nice bolt extractors broken off inside it. I JUST finished building the engine.

What have you guys used to get this thing out? Is there another place I can run the sensor wire to to get a good reading?

This car is an 86 with an 88 turbo engine and an Rtek 2.1. What repercussions are there to running without that sensor at all aside from the gauge not working? It needs to have an aftermarket gauge anyway and the FD guys seem to have an issue with rough idle and stalling while running without this sensor in place.

 

One of the things the sensor is used for is during hot starts.

 

Satch, he said the sender on the rear iron. You mean that sender is used for more than just the temp gauge, or did you misread?

 

The ECU gets it's coolant temp reading from the gauge on the back of the thermostat/water pump housing.

the only thing that gauge is used for is the temp gauge in the car, which you don't need since you have an aftermarket one.

if it doesn't leak I wouldn't worry about it

 

what he said

 

If it has the Yellow/White wire to it then it's for the gauge only.

 

I don't have an aftermarket gauge as stated. My friend should get one anyway. Again as stated.

I think the wire is yellow/red. But we are talking about the temp sender on the rear iron. The gauge worked but when I went to take the sensor out to paint the iron it came apart. I just need to know if I should just break down and take the rear iron off, drill it out, retap it and be done. I just don't have a lot of time.

I do however have a good temp sender laying around.

 

yellow red is the oil pressure sender.. yellow white is for water temp

you can relocate a factory sender.. or an aftermarket one.. to the bung on the front plate
.. it is down near the bottom on the CAS side of the plate and you can drill and tap it for the other sender

if you get it right, you can still mount the PS/aircon bracket over the top

as a side note.. s4 and s5 senders are different threads and i suspect range
and so making a franken engine brings the clash of a s5 rear plate with a bastard thread to adapt other senders to

 

PS

tap the bung to 1/8 BSPF 28 for mazda sender
or tap it to 1/8 NPT 27 for aftermarket sender

if your rear plate is s5

.. there may be limited options to tap it to a larger alternative thread and i would leave it alone

if s4 then you can go to the larger s5 thread if you make a mess of this one
( though you could try cutting through the brass to one edge with a dremel tip and folding it in on itself and pulling it out )

 

If it's not leaking, I'd suggest just leaving it. The prospect of screwing up the iron is fairly high. Then it will be a world of hurt as the engine will need to be disassembled.

Tap the water pump housing for a new guage sender and just extend the wire.

As mentioned, this sender is only for the gauge.

 

Thanks aaron. If it IS just for the gauge, I'm going to grind off the sharp edges of my broken extractor and leave it in there. This car is equipped with an Rtek 2.1, and he can see temp from the wp housing anyway via the Palm.

 

the range is different, i have an S5 sender in an early car, and the gauge is "hotter"

 

Are you sure? Because I too have an s5 engine in my s4 chassis. But the gauge had always read about 1/3 up. Which, if I'm not mistaken, is normal for s4. Recently however, my gauge has been steadily reading, and fairly consistently, 2/3 up. Hit it with the thermo gun and the temp is about 100*. So I do believe it's overheating slightly, and the gauge is reading as it should to s4 "spec"

 

I assume you have indeed checked the running temp to confirm that the engine is not actually running hotter? Also, that the sender you have is reading within spec?
I'm just curious to know, because as I'd stated I have the same setup, and had wondered this as well before I installed the engine

 

actually i just looked at my notes, and the two should be close enough. 80c is about 50ohms on the sender.

i'm actually about to make a gauge checker, Mazda has one in the FSM, but i think i'd like to be able to set the checker for different coolant temps, and see where the gauge needle is. TBD on the wiring/design of the thing, although one box should do the coolant, oil pressure and fuel level gauges

 

I did that in 2012 Mine includes a signal generator for the tahc & FD/Newer speedometers too

 

yeah? neat!

but it in a box with a **** labeled with coolant temp and needle position (it might be a confusing label), and i'd bet its marketable.

i'm going to make something just to calibrate me to the gauge.

 

In cleaning a Iron I noticed that the Big coolant hose and that sender share the same coolant passage.So If you tap the hose with some adapter you would,by rights, get the same reading that the original sender would get.
But,why bother..Right?.
If the old sender is Busted but sealed as not to leak,then I would tap the waterpump.It's neater..or use the engine coolant flush plug and put a sender there.

* aren't the s4 and s5 senders different in size,thread wise?

 

yep. they are not interchangeable

 

do you have a mazda NTC curve to share ?
im finding them difficult to quantify, online mazda ford charts do not match what i am seeing and i am trying to work something out for the early mazda dashes

i have found that up to about 86/early 87 mazda used the m8 x 0.75 thread and what looks like two different curves ( pre rx7 and rx7 )

most of these will throw an early ( pre 79 ) dash to 3/4 or almost hot when at operating temp when the original type ran the gauge about 1/4

for 87 and 88 they have used the 1/8 BSPF 28 gas thread and what looks like the same curve as the earlier rx7s
( same result on an rx2 or 4 dash at 3/4 )

my ( mazda ) sample of these ( about 10 of these mixed pre s5 rx7 units )
shows a 25 C measurement of 490 - 555 ohms

best i can manage at this point is it is looking like a 500 ohm shunt resister to push that curve colder and get those rx2/4 gauges to middle at running temp
( 1000 ohms makes it sit on the "warmed" mark on early dashes when at 90 C )

 

good news is that aside from tapping the m16 x1.5 bung in the front plate for 1/8 BSPF 28

you can also find mazda piston engine temp senders directly in m16x1.5 that will fit straight in

all FC engines share this bung , and with a bit of work,, we may be able to fix a resister to offset things
so that it can work to common middle point with either dash indication
( and also earlier rx7 and rx's )

 

OK.. here is the results of my quick test

O/T , the 76 rx4 likes 100 ohm as the middle of the temp indication sweep

testing various mazda temp senders i get these results

the test rig is a couple of alligator clips with appropriate connector, DMM, and a large alligator clip across the base of the sender
1 bag frozen peas and corn, microwave and at times some very hot water

temps are taken with infra red thermometer after 15 seconds immersion as the results steady out
there is some degree of error but they can be regarded as a fair sample

all R temps a in Celsius.. cause metric isnt 1700 AD backwards
- and after all it is a measure of water temp

temps over 100 are a little harder to quantify in this sort of testing and have been ignored

s5.. 1/8 BSPF 28 threads , spade fitting .. black ring
R0 ( zero Celsius .. AKA frozen peas and corn temp )= 2700 ohms
R25 = 676 ohms
R60 = 153 ohms
R80 = 62 ohms
R90 = 44 ohms

s4 ( late ) .. 1/8 BSPF 28 threads , bullet fitting .. black ring
R0 = 1700 ohms
R25 = 498 ohms
R60 = 125 ohms
R80 = 52 ohms
R90 = 43 ohms

s4 ( early ) .. M8 x 0.75 , spade fitting .. black ring
R0 = 1650 ohms
R25 = 515 ohms
R60 = 148 ohms
R80 = 44 ohms
R90 = 40 ohms

gen1 rx7.. M8 x 0.75 , bullet fitting .. green ring
R0 = 1480 ohms
R25 = 530 ohms ( three of these tested exactly the same here )
R60 = 140 ohms
R80 = 65 ohms
R90 = 46 ohms

i doubt any of these represent the old curve as seen in the early RX series
unless perhaps the older cars have approx 47 ohms resister offsetting the signal range colder
( which i expect takes the fidelity out of the display in temps above 100 C )

as is . if i add 47 ohm resister to a s5 sender that is at running temp of 90 C
then i get 47 + 44 = 91 ohms
.. which puts that needle just under halfway on the rx4 gauge

i am expecting now though that excessive engine temps may not fully push this needle to the top of the sweep
however, it will be obvious to the user that the needle has moved north of its happy spot just under half

and i think this best represents a solution for early RX
( without having to hack a new location, and find one of those elusive original senders )

 

i don't think simply adding resistance to a thermistor will be accurate. at one specific reading, yes. but a resistor will not react to temperature as a thermistor does.
or am i mistaken on what you're trying to achieve?

 

im trying to "fix" the old dashes to the new scale sender
as the pre 78 senders seem not to be in stock anywhere
,,, and the ones that are will push a gauge to almost max ( actually 3/4 ) when at the normal 90 C running temp

a resister will push the mid part of the range 'colder' on the display

i am aware that the sweep will never get higher than the minimum resister i have used

using a 47 ohm resister means the gauge will never pass that 3/4 mark

at this rate i am going to try around 33 ohms resister inline
and i expect the gauge will sit just over half at operating temp of 90C
,, but is still able to display to the top of the sweep when an overtemp ( more than 100 ) situation occurs

ideally i want to get normal temp near half sweep, and 120 C at the top of the gauge

as i am unable to reproduce an accurate 120 temp in a mug of water it makes me have to suck and see how it goes
( i may have to stick the probe into the roast beef to prove the high temp resistance of the post 78 senders )

 

Would the stickiness of the starch of the mashed potatoes alter the temp reading?.. Bumpstart??
(all those food references got me hungry!)