Water Temp Sender

[pochie45566]

Hi! I just bought a 1978 280z recently! Almost everything works except my water temp gauge. Ive determined its probably the sender has just crapped out but Id like to test it. Can anyone tell me how? i see the one wire going to the sender (yellow) and when i grabbed for it the whole plug came out and exposed a black wire but it doesnt come any further and I don't want to yank on anything. How do i get it so I can touch the temp sender wire to ground? Sorry for the idiotic question, but i'm new to this stuff. Ive worked on my own cars before but this is my first that has required more than a valve cover gasket and coils

 

while digging around trying to find the sender, I found this electrical plug coming from the rad hose on the bottom? Whats it for? 

Edited September 30, 2018 by pochie45566

[BJSZED]

I'm guessing the wire with the plug on it is an aftermarket coolant heater for cold climate winter starting. Looks like a 120 volt plug.

 

[cgsheen]

There are three sensors in the thermostat housing: Thermotime Switch (EFI), Temperature Sensor (EFI), Temperature Sender (coolant gauge).  The EFI sensors have 2-pin Bosch connectors.  The Temperature Sender has a male bullet built into the sensor (usually does not have a wire).  The yellow wire that connects to it has a female bullet.  There is no "ground wire" on this sensor.

 

The Temperature Sender is cheap and readily available (although all  the listings I see are for the sensor only and don't include the nut that goes over the barrel and holds it in place).  

Thermo_sensors.pdf

[NewZed]

14 hours ago, pochie45566 said:

 i see the one wire going to the sender (yellow) and when i grabbed for it the whole plug came out and exposed a black wire but it doesnt come any further and I don't want to yank on anything. How do i get it so I can touch the temp sender wire to ground? 

 

Should have posted a picture of that too.  There's also a switch on some cars.

 

Use a jumper wire to extend the circuit to ground.  Use a test light to make sure you're not shorting the circuit with no protection.  It might not like very low resistance.

[pochie45566]

On 9/30/2018 at 9:15 AM, cgsheen said:

There are three sensors in the thermostat housing: Thermotime Switch (EFI), Temperature Sensor (EFI), Temperature Sender (coolant gauge).  The EFI sensors have 2-pin Bosch connectors.  The Temperature Sender has a male bullet built into the sensor (usually does not have a wire).  The yellow wire that connects to it has a female bullet.  There is no "ground wire" on this sensor.

 

The Temperature Sender is cheap and readily available (although all  the listings I see are for the sensor only and don't include the nut that goes over the barrel and holds it in place).  

Thermo_sensors.pdf

Sorry for the late reply.

 

Thanks for that, I thought something was wrong but somehow I read somewhere that theres a ground wire which didn't make any sense to me. Can someone tell me the proper way to diagnose the temp gauge problem then? more the sender I guess. I've read that mostly when these things crap out its the sender. but it could also be the wire from the sender to the gauge or the gauge itself. 

[cgsheen]

Well, the temperature sender itself is just a thermistor - a variable resistor that changes with heat.  There's a chart in the FSM with approximate resistance values at various temperatures.  Easy to test with a multimeter - one probe to ground, one probe to the male bullet on the end of the sender.

 

Otherwise, it's following the circuit diagram and testing the wiring, connectors, and the gauge...

[jhm]

This may not help with your immediate problem.....but once you get things working,  you can physically test the accuracy of the temp sensing system with an IR gun....see if you're getting the same readings on your gauge as you get on the gun.

 

If you determine that your sending unit is out of spec, a new one can be purchased here:  http://www.thezstore.com/page/TZS/PROD/16-7110

[NewZed]

12 hours ago, pochie45566 said:

I read somewhere that theres a ground wire which didn't make any sense to me.

 

There's a ground wire on the switch used for the dual pickup distributors.  Your 78 doesn't have that.  But after 40 years there's no guarantee that your car is still all 78.

[pochie45566]

Ok thanks guys, I think ill just replace it and see what happens. I think it’ll fix the issue, ive read the oem one is pretty fragile. If it is oem. Lol. Ill report back soon. 

[pochie45566]

Ok sorry guys, gotta ask what’s going on here. Do I need to remove the retaining nut to access the sender? This yellow wire coming off the sender doesn’t want to come off and I don’t want to tug too hard. Not sure if this is oem or not. How do I get to that retaining nut also without removing the yellow wire?

 

[NewZed]

Grab the rubber end and twist it to break it free.  Stick a wide screwdriver in between the edge of the rubber and the nut and twist it or push, to push the rubber off.  It's factory stock and actually looks in good shape.

 

You could remove the nut but the sender might still be stuck in the bore.  And coolant will leak from the hole if you remove it.  Use a pair of pliers on that rubber end and it will pop off.  Don't pull on the wire.  Just work it around until it comes off.

 

[pochie45566]

25 minutes ago, NewZed said:

Grab the rubber end and twist it to break it free.  Stick a wide screwdriver in between the edge of the rubber and the nut and twist it or push, to push the rubber off.  It's factory stock and actually looks in good shape.

 

You could remove the nut but the sender might still be stuck in the bore.  And coolant will leak from the hole if you remove it.  Use a pair of pliers on that rubber end and it will pop off.  Don't pull on the wire.  Just work it around until it comes off.

 

 

Ok, so I got that whole rubber assembly out but it just led to a black wire going further into the thermostat housing and that wire doesn’t want to budge. I thought I’d find the sender in there lol. Thank you very much for your help newzed. 

[NewZed]

Your picture doesn't show where a "black wire" would be.  A picture of the mysterious black wire would help a lot, I think.  The picture you posted looks like the correct yellow sender wire, clipped on to the end of the sender, and protected by a rubber end.  The rubber piece is on the outside already.  not sure what's coming "out".

 

Are you saying that the shiny black material is "rubber" and that the whole thing came out?  That's not a stock piece then, I think.  Not sure why there would be a wire left over either.

 

[pochie45566]

24 minutes ago, NewZed said:

Your picture doesn't show where a "black wire" would be.  A picture of the mysterious black wire would help a lot, I think.  The picture you posted looks like the correct yellow sender wire, clipped on to the end of the sender, and protected by a rubber end.  The rubber piece is on the outside already.  not sure what's coming "out".

 

Are you saying that the shiny black material is "rubber" and that the whole thing came out?  That's not a stock piece then, I think.  Not sure why there would be a wire left over either.

 

Here’s what I’m talking about, when trying to twist that rubber end off, the whole thing came out revealing a black wire. 

[NewZed]

I tore my coolant temperature sensor apart like that on my 76.  Oops.  The coolant temp. sensor has a well like yours.  Somebody might have repurposed one on yours.

 

Not really sure what to tell you now.  You might work your way back on the yellow wire and see if there's a bullet connection in to the harness.  Take it apart there.

 

Or you could just buy a new sender.  One problem for you though is to be sure you have a spot for in the T-stat housing.  Nissan used several different bore and thread sizes.  I think that all four holes are different.  Looks like you're n the right hole though.  Not sure what a PO put in there.  Flip the picture 90 degrees in your head...

 

 

 

[pochie45566]

15 minutes ago, NewZed said:

I tore my coolant temperature sensor apart like that on my 76.  Oops.  The coolant temp. sensor has a well like yours.  Somebody might have repurposed one on yours.

 

Not really sure what to tell you now.  You might work your way back on the yellow wire and see if there's a bullet connection in to the harness.  Take it apart there.

 

Or you could just buy a new sender.  One problem for you though is to be sure you have a spot for in the T-stat housing.  Nissan used several different bore and thread sizes.  I think that all four holes are different.  Looks like you're n the right hole though.  Not sure what a PO put in there.  Flip the picture 90 degrees in your head...

 

 

 

I’m in the right spot for sure. I’m just a bit lost on where to go from here lol. I would put a new sender in but that wire is attached to something in there and I don’t want to yank on it. 

 

The water temp gauge doesn’t come up on my chiltons service manual either in the diagrams or else I’d just redo the wiring for the gauge from the start. Advice on where to go from here to get that sensor to work? Im sure it’s not as simple as ripping out that wire and putting a sender in lol. 

 

Edited October 3, 2018 by pochie45566

[NewZed]

The thin wire is probably soldered to the bottom of the well where the actual sensing element is.

 

Follow the yellow wire back in to the harness until you find a break.  I don't think it goes all the way to the gauge.  Probably a bullet connector somewhere.

Edited October 3, 2018 by NewZed

[jhm]

If you only have a Chilton's manual for reference, that's part of the problem right there.  Aftermarket service manuals are often questionable....sometimes they're useful, sometimes not.

 

If you don't have the Factory Service Manual, you can download it for free at:  http://www.xenonzcar.com/s30/fsm.html.  I've attached the Body Electrical chapter here to get you started; gauges start on page 31.

Body Electrical.pdf

[cgsheen]

Look at the picture of the temperature sender.  The "top" has come off - I could tell that from the black goo oozing out in your pictures.  That black "wire" you're pulling out is the internal wiring to the thermistor.  It's broken so you don't need to be gentle with it anymore!  Pull it out and disconnect the yellow wire from the top of the  sender...

 

Remove the nut and pull out the rest of the sender from the thermostat housing.  Buy a new temperature sender online or at your local parts store and get it installed.  (Save the "hold down" nut just in case the  new sender doesn't come with one.)  Nissan used the same resistance value for these senders for many years of Z's (and ZX's).   

[pochie45566]

15 hours ago, cgsheen said:

Look at the picture of the temperature sender.  The "top" has come off - I could tell that from the black goo oozing out in your pictures.  That black "wire" you're pulling out is the internal wiring to the thermistor.  It's broken so you don't need to be gentle with it anymore!  Pull it out and disconnect the yellow wire from the top of the  sender...

 

Remove the nut and pull out the rest of the sender from the thermostat housing.  Buy a new temperature sender online or at your local parts store and get it installed.  (Save the "hold down" nut just in case the  new sender doesn't come with one.)  Nissan used the same resistance value for these senders for many years of Z's (and ZX's).   

 

Thank you! I think that black glue is something that the past owner used to glue that back in, it feels hard. Someone mentioned here if i take off that nut that coolant will come out? Then once its out I can just put a new sender in, use the retaining nut, then attach the yellow hose to the end.