B&M Transmission Temp Gauge - No Reading

[TheSloMoShow]

Hello everyone,

I just installed my lovely temp gauge.

It'd all wired up, but I'm not getting a valid reading. The gauge illumination works, but the needle stays below 100 F.

Either my temps aren't reaching (I doubt it, even though it's 10 F here in Ohio) or the wiring isn't done correctly.

I've wired the "GND" post on the gauge to battery negative terminal.
I've wired the "-" post on the gauge to the sender, which is installed in line with the cooler OUT kine just before it enters into the tranny cooler side of the radiator.
I've wired the "+" post on the gauge to the pnk/bwn wire on the rear windshield wiper motor so that it is ignition switched.
The gauge illumination is also wired to this same pnk/bwn wire so that it illuminates when ever I turn on my ignition.

I've driven it now a pretty long distance just to ensure transmission is up to operating temp, yet the needle hasn't moved.

Any ideas what the issue could be?

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[90xj06]

make sure the body of the sending unit has a good connection to ground.

 

[TheSloMoShow]

make sure the body of the sending unit has a good connection to ground.

I had read this earlier on in the instructions. I was confused, as I assumed it was grounded just by being in line with the hard cooler line itself.

I purposely didn't use any Teflon tape to seal any of the T fitting, or sender to avoid problems with grounding.

Am I to add a second line that goes from sender to chassis ground (same ground as for GND post)?

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[90xj06]

the hard line may not have a good connection to ground. you can check it with an ohm meter from sender to battery negative.

 

[90xj06]

and you can ground it anywhere on the body. it does not have to run back to the gauge.

 

[TheSloMoShow]

and you can ground it anywhere on the body. it does not have to run back to the gauge.

I did that last night with just a bare wire and stuck it in the ground spot by auxiliary fan and radiator support bracket. It shot the temp gauge up to 350. Maybe it shorted.

I'll go through again here in a few to make proper ground is established for sender body. Hopefully it does the trick.

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[lazyxj]

Use a ohm meter to see if the sensor is still good. The sensor will burn out if accidentally exposed to 12-volts,

 

[TheSloMoShow]

Ok, so I tested for ground (continuity between sender and chassis). Came back very close to 0. I believe grounding is not the issue.

I did accidentally touch the + post and sender gauge post while installing the gauge. It blew out two 25a fuses in my junction box. Perhaps I burnt the sensor out.

How would I test if it's burnt out....Test for resistance and if it comes back OL it's bad? Red probe to the sender's sensor and black probe to the tip where the signal is sent?

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[90xj06]

i would gather if you ground the wire going to the sensor the gauge would jump. up

 

[TheSloMoShow]

I took the sender out.
Put it into a hot pot of water (just the sensor).
Then pulled out and tested resistance on my table. Less than an ohm resistance, but slowly climbing up in resistance as it cooled off.
I think the sensor is OK.

So I put it back in, and checked again for ground at the sending unit.
If I probe at the tip of the sending unit, just past the last nut, it measures nearly 170 ohms.
I probe anywhere else on the sensor (threads etc), the T fitting or the hard line and it's in open loop.

I'm assuming this means it's not properly grounded?

Sounds like a silly question, but how do I go about properly grounding the unit? I can't attach any wires to the tip or it'll just interfere with the sensor wire and cause it to read 350 F.

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[TheSloMoShow]

Would it matter if I used a thicker gauge wire to connect the sender unit to the gauge? The wire that comes with the kit is about 18-20 ga. Too thin I thought. So I hooked up 14ga for all 3 posts. I don't think this matters, but I thought I would mention it.

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[D.I.T.A]

Do you have a cooler on it bypassing the radiator ? my temp gauge doesn't budge on the 30 minute commute to work once it drops below 40 degrees out side unless I do stop n go then it will hit about 140 .

 

[TheSloMoShow]

Do you have a cooler on it bypassing the radiator ? my temp gauge doesn't budge on the 30 minute commute to work once it drops below 40 degrees out side unless I do stop n go then it will hit about 140 .

Nope, stock setup. Was thinking about adding a cooler based on how the tranny temps reported back.

I'm thinking the gauge is actually working, maybe the transmission just isn't getting warm enough in this single digit weather.

The longest commute I've had since the sensor was installed is 15 min.

Guess I'll give it some time.

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[lazyxj]

I'm thinking the gauge is actually working, maybe the transmission just isn't getting warm enough in this single digit weather.
The longest commute I've had since the sensor was installed is 15 min.

To test the installed sensor in cold weather, heat it with a hair dryer or heat gun.

 

[TheSloMoShow]

To test the installed sensor in cold weather, heat it with a hair dryer or heat gun.

Didn't work had it pretty hot with the heat gun from Harbor Freight.

So testing continuity/ground from the sender's tip where the wire connects, it's showing large resistance. 170 ohms. I measure anywhere else on the sender's body (threads by the coupler, T fitting itself) it's less than 1 ohm resistance.

So it seems it's grounded properly I believe....

I may just buy a new sender and swap them out to see if for some reason the sender is just faulty.

Does using a larger gauge wire have any impact to the gauges reading of the sensor?

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[whitexj98]

My B&M gauge will move just a bit with the 12v to it. I would check the + terminal at the gauge for voltage.

 

[trippled]

Before you go through that, have you taken it on a good long drive? Like 20 miles or more? The more shifting you do the better, just to see. And no, as long as the wiring is good, the size really won't make a difference.

 

[TheSloMoShow]

My B&M gauge will move just a bit with the 12v to it. I would check the + terminal at the gauge for voltage.

Once I turn my ignition on, it will move a slight bit (maybe 1/8"). So I know some power is getting to it. That same ignition source is also powering my gauge illumination.

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[TheSloMoShow]

I gave the tranny a bit of a workout today, driving > 30 minutes. The temp gauge rose more than it has in the past, but still didn't make it just yet to the 100 line. Perhaps it's accurate, and the ATF just isn't getting heated up in this cool weather.

Do the results of my resistance test on the sensor seem to be kosher tho? My thought would be that when the sensor is hot, the tip should measure minimal resistance unlike my results which showed nearly 170 ohms. But the rest of the body and T fitting tested OK.

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[trippled]

You'd need a sensor range chart to be able to accurately tell, and it could depend on what style of temp sensor it is. Another idea is to use an ir temp gun and measure the temp of the sender and compare to the gauge