I need a electrical wizzard for fixing a temp gauge

[348tripower]

I have been running the hemi and shooting it with the Fluke temp gun. I have about 30 degrees difference between my gauge and the gun. The gauge reads hot.  Can I adjust this with a resistor ? If so what would I use? I'm not that smart today  
PS I see that these things run 203 degrees with two fan settings of 209 for low and 219 for high.
I was reading about 210 on idle and checked it with the gun and got 180.
=30 degrees

[enjenjo]

A resistor is not going to do it. The way an analog gauge works is by varying the resistance to change the voltage to the gauge. so unless the gauge reads 30 degrees high over the whole range, the gauge will only read right at one voltage. Now if you can find a sending unit with another resistance range that is correct cold and hot, that would work.

If you are running computer controlled gauges with stepper motors, the output from the computer determines the gauge reading. So GIGO. And if you have removed the sending unit for the computer, and reinstalled it, they seldom read correctly. So I always use a new OEM sender.

[kb426]

Is there 2 temp sensors on the engine? One for the gauge and 1 for the computer?

[enjenjo]

Is there 2 temp sensors on the engine? One for the gauge and 1 for the computer?

Some times yes, some times no. Analog gauges normally use two senders. Computer gauges use one most of the time. Of course with a computer it can have several temperature inputs. Ambient air temp. Intake air temp. Coolant temp.

[wayne petty]

not a rocket scientist here..

you need a DPST ON-ON or ON-OFF-ON toggle switch..

you will need to pick up 2 of these.. hopefully radio shack still exists..

https://www.radioshack.com/collections/trimmers-thermistors/products/1k-ohm-15-turn-pc-mount-cermet-potentiometer-trimmer

and 2 of these..

https://www.radioshack.com/collections/trimmers-thermistors/products/radioshack-10k-ohm-15-turn-cermet-potentiometer-trimmer

why.. because they are cheap.. and you have several uses for them like bypassing failed Vats ignition lock cylinders when you have the proper key to measure the resistance .. using the first and second or second and third to match the key resistance.

you should have  a ground clip  off the middle wire of each switch..  the toggle switch outer terminals connected to the first terminal of each switch.     the center wire of the toggle switch hooks to another gator clip that hooks to your existing sending unit wire disconnected from the sending unit on the engine..  you can then flip the switch in one direction and adjust the small screw on the end of the blue resistor till the temp gauge reads 100F... flip the switch and adjust the other one till your gauge reads 240 on the gauge..

disconnect this unit..  now go ohm it..   see how much resistance you need for 100F.. and how much you need for 240F..  post that info..  post what thread size the sending unit is..     both the NAPA and the BWD electrical parts catalogs have 2 or 3 pages of temp sending units of many resistances and thread sizes..

a few years ago.. i helped somebody find something that would work with their stock late 60s or early 70s GM temp gauge..  it turned out to be a VW sending unit that was really close at 220F.. to the resistance needed.  who cares if your engine is 100 or 120F.. you want to make sure its NOT running toooooo HOOOOTTTTT..  somebody here ended up needing a 8 or 9mm tap with 0.8 pitch as i recall. and they drilled a brass hex pipe plug to make it fit the opening.

since you did not list any info about which gauge you are using..  or which sending unit..

if one is really smart.. one can get a DPDT switch also..  ON-ON.. or ON-OFF-ON.. so you could switch between the 1K and 10K pots on each side..   i can draw this up .. if you want.. its not hard to do.. and i know that people are quite capable on this site. with just a little nudging from my brain.


one can find the napa catalogs here.. i don't recall which ones its it.. i know there are 2..  could be the 4th down or the bottom one..  once the catalog loads and its like 500 pages.. there is a link to start a PDF download in the header if you put your cursor up there. ..

http://www.napaechlin.com/en/catalog/pdf-catalogs/


actually it looks like DIgital pages 22 to 34. .

http://www.pageturnpro.com/Four-Seasons/73620-Engine-Management-Reference-Guide/index.html#2

[348tripower]

Is there 2 temp sensors on the engine? One for the gauge and 1 for the computer?

It now has two senders as I had to add one for the gauge.

[348tripower]

The gauges are Omega and I do have the resistance values for the sending unit. I will post them later from the work shop. It is a 1/8 NPT unit.

[348tripower]

100 deg 450 ohms
150        158
175         99
200         64.3
250         29.6
Wayne,
Thats the info. Would this nee a higher ohm sender at 100degrees or lower?

[wayne petty]

100 deg 450 ohms
150        158
175         99
200         64.3
250         29.6
Wayne,
Thats the info. Would this nee a higher ohm sender at 100degrees or lower?

this might be worth a try.. the specs are written strange.  but it might be the exact sending unit you need.

https://www.napaonline.com/en/p/ECHTS6035

C@100 460Ω w/5% Tol, O@220°F 36Ω w/10% Tol 1⁄8 x 28 Tapered pipe


this might even be closer.

TS6723 1 threaded stud G - 450Ω @100°F w/18% Tol, 46.6Ω @220°F w/12% Tol 1⁄8 x 27 MPT
https://www.napaonline.com/en/p/ECHTS6723

do me a favor.. spend a few minutes and run the voltage drop test also.. at least the first 4 steps..

http://i.imgur.com/Mo57rdb.jpg

why..   the sending units require the ground between the engine and the cab for the negative side of the connection..

if you have a remote mounted battery..  you can hook up a single jumper cable laying beside the vehicle to hook one of your volt meter probes to for tests 2, 3 and 4...   if you wanted to do 5 and 6... six is really important for alternator service life. as are 2 thru 4.   you won't have the proper amount of voltage on the negative side.

practice on daily drivers to see what good readings are.. and to verify they are working also. i can do tests 1 thru 4 in less than a minute.

Edit.. you might actually try both senders to see which one is closer in boiling water ...

you will need to add make up a brass fitting with  a ground wire wrapped around it so you can dip the entire fitting end in boiling water in a styrofoam cup.

Spend 5 minutes with some graph paper and plot the resistance.

[348tripower]

Wayne,
I'm in the process of swapping out a turbo 350 for a 700r4 in a 1938 Chevy
I will get back to the wagon after this job. i did find that I can read the live data on the computer and see what temperature the computer is reading.  So I'll check that too. I will report on my findings.
Thanks!

[wayne petty]

Wayne,
I'm in the process of swapping out a turbo 350 for a 700r4 in a 1938 Chevy
I will get back to the wagon after this job. i did find that I can read the live data on the computer and see what temperature the computer is reading.  So I'll check that too. I will report on my findings.
Thanks!

please make sure that you have the carb linkage ratio adapter.. but you know this..

[papastoyss]

Don, my ls1 '40 coupe reads about 15 or so degrees higher on my scanner than the reading on the Dakota Digital dash. The sender for the ecm is in the exhaust flange, the sender for the dash is in the water pump by the upper rad hose.Could sender location have any bearing on your readings?