Temp Gauge Issue

[Jimjific 23]

Need some help on this one.

 

- The temp gauge has never read since I've owned the car.

- I have tested the gauge by shorting out the connector and the gauge pegs to hot and then goes back when the connector is "open".

- I took out the temp sensor and hocked an ohm meter to it and the value changes when I put a torch to the bottom of the sensor.

 

I tried another sensor that I found on a spare manifold. I have no idea what it is off of. It was quite different though (It had two connections and it went deeper into the manifold). This one pegged the temp gauge when I wired it to the the one terminal that responded to heat. So I took that on out. and put the original back in. Any ideas of why this sensor would respond to heat yet not work?

 

Thanks,

Jim

[69gmachine 15]

It sounds like you have a switch for an idiot light instead of the sending unit for a gauge. They're cheap and readily available at most any auto parts store, so I would just go get a new sending unit.

 

They also look almost identical. The only visible difference is the color of the plastic insulator around the stud where the wire harness attaches.

 

You can test it by momentarily grounding the lead to the engine. The gauge should go full scale.

[Midlife 814]

It sounds like you have a switch for an idiot light instead of the sending unit for a gauge. They're cheap and readily available at most any auto parts store, so I would just go get a new sending unit.

 

They also look almost identical. The only visible difference is the color of the plastic insulator around the stud where the wire harness attaches.

 

I'd agree with this possible scenario, based upon the evidence presented.

[Print Dad 58]

Hello Jimjific,

I would like to consider myself pretty "up" on this.

I fought issues on our Mach for the whole summer

before I finally got things working right

 

I agree you have the wrong sensor. I also agree you need to

swap the sender - - -Here is where I learned through a LOT of

aggravation - - I tried several senders from a few manfacturers

and they worked BUT not accurately.

I finally spent a little more and bought a Motor-Craft sender

and everything works GREAT.

 

I tested the OHMS resistance of several "new" cheaper senders

and the resistance varied a LOT from one to another and that

was new out of the box

 

My advice - get a new Motor Craft sender - you will pay more

BUT I bet is works great at least it did for me

 

Print Dad

[Jimjific 23]

Thanks for the advice. Unfortunately, I read it this morning and last night I ordered a cheap one. If it doesn't work, I will get the Motor craft one.

 

Last night when I was doing some research on it, I found a message board that was discussing it and it said that when the engine is hot, the sensor should read ~25ohms and a way to test this is to get a 25ohm resistor and see if your gauge goes to the middle. I didn't have one on hand but I figured I'd see where I was at with the sending unit. I had driven the car earlier so it wasn't completely cold and the sensoe read ~100ohms. I started the car and let it run and get hot and the sensor only went down to ~65ohms. So it moved but just not enough.

 

Jim

[Midlife 814]

Thanks for the advice. Unfortunately, I read it this morning and last night I ordered a cheap one. If it doesn't work, I will get the Motor craft one.

 

Last night when I was doing some research on it, I found a message board that was discussing it and it said that when the engine is hot, the sensor should read ~25ohms and a way to test this is to get a 25ohm resistor and see if your gauge goes to the middle. I didn't have one on hand but I figured I'd see where I was at with the sending unit. I had driven the car earlier so it wasn't completely cold and the sensoe read ~100ohms. I started the car and let it run and get hot and the sensor only went down to ~65ohms. So it moved but just not enough.

 

Jim

If you have a stock dash, then that definitely is the wrong sending unit. Sometime about '74 or so, the TSU's changed to a larger range of resistance from 13-78 ohms to something to greater than 100 ohms.

[Jimjific 23]

Well the issues continue. Here is an image of the sensor that was currently on the engine.

 

 

 

Here's the one I bought from e-bay with discription:

1969-1973 Mustang Water Temperature Sending Unit WITHOUT TACHIOMETER

 

 

 

That is their spelling of tachometer not mine. They say in the add that it is a Scott Drake unit. Well anyway, it didn't work. I had a feeling it wouldn't since it looks different and the threaded tip is smaller too. I had to pinch the connector that pushed on to it. I'm not sure why this is such a pain in the you know what. It's not like ford didn't make millions of 302 motors.

 

Jim

[69gmachine 15]

From your measurements you've established you have the wrong sensor. I would go to a local auto parts store and bring your multi meter. Ask the clerk to let you take a reading so you can verify it's rougly 78 ohms when measured at room temp.

 

Regardless of whether or not you have a tach, the only thing that matters is that you need a sending unit for a gauge, and using the early voltage range scale. Just because the Scott Drake part doesn't look OEM, doesn't mean it shouldn't work. But if they package it as being for a non-tach car maybe they have it mis-identified. I don't know enough about the '67/'68 cars to know for sure but maybe they use a switch for an idiot light for non-tach cars and they assumed the 69s are the same? The '69/70 tach cars use a temp gauge, and apparently so do the non-tach cars.

 

At any rate, I got mine from Autozone for dirt cheap and it works great.

[69ISH 10]

Well the issues continue. Here is an image of the sensor that was currently on the engine.

 

 

 

Here's the one I bought from e-bay with discription:

1969-1973 Mustang Water Temperature Sending Unit WITHOUT TACHIOMETER

 

 

 

That is their spelling of tachometer not mine. They say in the add that it is a Scott Drake unit. Well anyway, it didn't work. I had a feeling it wouldn't since it looks different and the threaded tip is smaller too. I had to pinch the connector that pushed on to it. I'm not sure why this is such a pain in the you know what. It's not like ford didn't make millions of 302 motors.

 

Jim

I am having the same issue with the Scott Drake sender units and I have bought 2 of them and they both don't work, I have fitted a 67 sender unit and that works but the gauge reads a lot higher than it should.

[Jimjific 23]

I just bought another one from Autozone and it showed ~45ohms cold so I was hopeful. I did a quick test buy hooking it up with leads and taking a torch to the sensor and the gauge didn't move at all. The gauge still pegs when grounded. I might have to take Print Dad's advice and get the Motorcraft one. I just have to find a source.

 

Jim

[Jimjific 23]

I finally got the temp gauge to work. After getting one off of e-bay that didn’t work, I went with Larry’s advice and got one from Autozone and it worked. Here is a write up of how I tested the sensors and gauge in case someone else needs to go through this.

 

Things that you will need or really help to understand what is gong on:

- Volt meter

- 22 Ohm resistors (not 22 kOhms, I made this mistake by not reading closely.)

- Wire leads with alligator clips on the ends. (Not mandatory, but they make life a lot easier.)

- A way to boil water. (I had a hot plate so I was able to do this in the garage. Always makes the wife happy if I can keep car parts out of the kitchen.)

 

The first thing to rule out is a faulty gauge. This is easily done by pulling the connector off of the sensor and put the connector to ground. Check the gauge in the dash and it should be pegged to the hot side. Mine did this so I knew the gauge worked to that point.

 

The next test for the gauge that will let you know that it is “calibrated†somewhat is to test it again with a resistor between the connector and the ground source. I got these resistors from Radio Shack (Yes, they still sell some electronic components, but nothing like they used too) for about $1.60.

 

Here is a quick diagram of how it should look hooked up.

 

Check your temp gauge again and it should read about half. This lets you know that if you can get your sensor to read ~22Ohms in hot water, it will read on the gauge. I did one more quick sanity check by putting two resistors in series giving me 44 Ohms and checking the gauge again and it didn't move. This means that the gauge range is somewhere between 0-44 Ohms.

 

Next I tested the various sensors that I had. You will need a Volt meter that can read resistance. Put the setting to read Ohms. I got the hot plate out and put some water in a pot. You should hook everything up like this.

 

I took the lead that connected to the threaded end and wrapped it around a screw driver that I had resting on the top of the pot so the sensor would hang in the water without touching the bottom. You want to make sure that it doesn’t touch the bottom since you want the sensor to read the temperature of the water, not the pot or hot plate since they will be hotter than the 212 degrees of the boiling water.

 

I had three sensors to test:

 

- Original one that was on the car.

- One I got from e-bay.

- One from Autozone.

 

Here were my results:

 

- The original one started at ~400 Ohms and came down to 92.8 Ohms in boiling water. 92.8 is to much resistance for the gauge to move.

 

- The e-bay one bounced around in the milli Ohm range and went to open when put in the boiling water. This suggests that this sensor is only for an idiot light and not a gauge. This by the way is not how they advertised it.

 

- The Autozone one started above 100 Ohms and came down to 32.4 Ohms. So it looked like we had a winner here.

 

So I installed the sensor and ran the car. It's always fun to have another excuse to take the car out for a drive. The sensor worked great. The gauge crept up to about half and then you could tell that the thermostat opened since the gauge settled back down to about a third. Now I can drive with a little more confidence.

 

I know it was a long post, but I figured it might help some people out there.

 

Jim

[tonyinsandiego 37]

It appears I have a temp gauge problem.  My gauge is pegged to hot right away.  I added a resistor (25 Ohms) between the temp wire to sensor and ground but the gauge still pegs.  This is why I believe I have a temperature gauge problem.  Do the experts in this thread concur and where can I get another temp gauge if needed?

 

Cheers everyone

[SA69mach 39]

Sounds like your sending wire is grounding somewhere along its path from gauge to sending unit.  A gauge that pegs immediately to HOT is sure sign it is grounded.

 

Check the entire length of the wire in the engine bay and through the firewall for rub-thoughs, burns or breaks.

 

Next, you need to test the resistance value of the sender unit in the manifold.  As depicted above, take a resistance reading from sender tip - ground with the engine cold.  In ohms, you are looking for around 78 ohms. 

Warm up the engine and monitor the resistance values with the ohm-meter.  If your temp sender is a 'gauge' type (and not an "on-off" switch style) you should see a linear change in resistance values as the temperature of the engine rises - the ohms will get lower, and hold steady at something like 33-45 ohms.

 

That is a test worth doing and reporting.  We can go from there...

 

One thing to note is you ought not run your gauge on "pegged hot" for any extended period.  It can damage the gauge internals.

[69volunteer 84]

where can I get a 'motorcraft' temp sender and does anyone have a part number?

[Brian Conway 264]

I have posted this page several times on this web site for discussions asking the same sorts of questions. You will need to pay attention to the correct sender part number, the SW number and gauge or warning lights. These units are around but you will need to do some digging. I found the correct Autolite and Motorcraft units for my car at about the same time so I bought them both. Costing about $35.00 each. Very happy that I put in the extra time, effort and money. Brian

[69volunteer 84]

Brian-

I've used that sheet of yours multiple times searching. I cant find anything on ebay or any of the parts stores that match up or are "motorcraft/autolite". My local NAPA is usually pretty good but they don't have a match and the NAPA brand echler unit was similar to all the others.

 

The other stores are hopeless--I once had a kid behind the counter ask me "what are points?" when I tried to buy a new set.

 

I'll keep looking.

[Brian Conway 264]

Well I said " you will need to do some digging " not shopping.  The NOS guys will have these parts not NAPA or PEP BOYS.  That's why I paid $35 and not $12. Try: Mustang NOS parts, Green Sales Co., Back Counter Parts or Miller Obsolete Parts.  The internet and the search engines are where you are going to get the stuff you want.  Brian

[barnett468 418]

.

to plot the sender, put water in a small pan with around 1/8" cup of salt.

 

clip a candy temp gauge to the side of the pan . . i think martha stewart sells them.

 

clip a wire lead to the body of the sender and another to the post.

 

put sender in a small strainer and suspend the strainer over the top of the pan with the sender submerged at least 1 inch . . dont let the post of the sender touch the strainer.

 

turn stove on and take sender reading every 20 degrees until water reaches at least 200 degrees.

 

 

to test gauge range, buy an adjustable ohm box.

 

.

[Brian Conway 264]

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CB4QFjAA&url=http%3A%2F%2Fwww.greensalescompany.com%2FPages%2FPN%2FC9WY10884A.html&ei=LTxAVaK0Dci2ogTrnoGYAw&usg=AFQjCNHvwRAkAywziJKRdqydm5fLqjBf-A

 

Try these guys.  Brian

[SA69mach 39]

you can make a test tool easily. 

 

link here - 10 dollar , 2 hour investment.

 

http://1969stang.com/forum/index.php?/topic/52736-make-a-tool-to-test-your-gauges-easy/?hl=%2Bmake+%2Bgauge+%2Btest

[tonyinsandiego 37]

I did a few checks today and I can't see anything obvious in the engine bay.  I read across the sensor and this is approximately 800 ohms cold and around 25 Ohms hot (boiling water).  The senser appears to work okay.  Maybe not exactly factory specs but shouldn't peg the gauge.  If I read across the wire to ground I get about 125 Ohms.  I definetly have something shorted across the wire.  This could be under the dash or possibly a shorted gauge.  I can test the gauge by taking my oil pressure wire and hooking that up to my temp gauge.  Best case is remove the wire from the gague and attach the oil pressure wire directly to the gauge. 

 

I apparently have to remove the dash pad and gauge cluster to play around a little more.  Let me know if you guys think I'm on the right track.

 

Cheers

[barnett468 418]

.

if the wire to the sender is grounded, the gauge will go to high in around 5 seconds when you turn the key on.

 

unplug the wire from the sender and dont let the end touch the engine and turn the key on and watch it.

 

you should have resistance at that wire with it disconnected, its just the way it works.

 

if the wire was grounded to the body, it would peg the ohm meter.

[SA69mach 39]

I did a few checks today and I can't see anything obvious in the engine bay.  I read across the sensor and this is approximately 800 ohms cold and around 25 Ohms hot (boiling water).  The senser appears to work okay.  Maybe not exactly factory specs but shouldn't peg the gauge.  If I read across the wire to ground I get about 125 Ohms.  I definetly have something shorted across the wire.  This could be under the dash or possibly a shorted gauge.  I can test the gauge by taking my oil pressure wire and hooking that up to my temp gauge.  Best case is remove the wire from the gague and attach the oil pressure wire directly to the gauge. 

 

I apparently have to remove the dash pad and gauge cluster to play around a little more.  Let me know if you guys think I'm on the right track.

 

Cheers

I think you are on the right track

What year Mustang?

[tonyinsandiego 37]

Glad to hear I'm on the right track.  I have a 66 GT with inoperable blinkers that kicks butt, unfortunately it's my butt.  Still working through that too.  I have a 1969 Mach 1 and a 66 GT coupe. 

 

[tonyinsandiego 37]

Ok I pretty sure I found the root cause of the temp problem pegging out,  Looks like the PO had this wire hooked up to an electric choke.  I guess any available wire will do if it's not connected to anything.  I actually thought this was working at some point in time but that was a while ago.  Anyway now I know what the problem is and I can easily fix it.  I starting looking at schematics to see what wires went to the gauges,  It looks like only one connector is used for the oil P/Water T/coil power.  Thought someone would like an update.  Next is geting the tach and ammeter working.

 

Cheers