Faulty Temp sending unit??
 

My temp gauge wasn't moving above 100 so I did the grounding tests etc mentioned in some previous threads and found the gauge acted as it was supposed to so I moved on to the temp sending unit and ohm tested it proving it was faulty. Went to NAPA and they didn't list a Corvette sending unit but had one listed for 327 Camaro that looked just the same. After installing the new sending unit and a new 180 thermostat (there had been a 160 in the car) I ran it for awhile and it reads to top of gauge near 240 after running awhile. It cools back to 100 on gauge when it sits for an hour or so and then slowly back to 240 when it runs. I replaced the 180 thermostat with the old 160 and still get the 240 on the gauge while running which leads me to the temp sending unit again. Sorry this is so long but now the question. Would there be a difference in internals between a temp sending unit for a 327 Camaro and the 327 Corvette that would lead to my gauge reading so high? I don't have access to a thermal testing gun to check the real temp. Thanks. :thumbs: Dave

Dave, the theromsat has nothing to do with your problem. Once it's open, weather 160, 180, it's open. That's it. The rising temp is engine or radiator related.
Suggest you find a garage that has a IR gun and have them shoot the temps at the thermo, bottom and top radiator hoses, hope this helps, Bill.

Thanks Bill. I guess it would be best to get the true temp by getting the heat checked and then go from there. The car has never overheated (original radiator too) and up until taking it out of storage this year and seeing nothing register on the temp gauge it always ran with the needle on the cool side of 180. I think I've probably got a faulty new sending unit but I'll have the IR test before getting another one. Thanks for clarifying the thermostat thing for me. :thumbs: Dave

hot...
 

Dave, just been down this road. There are several available T-senders available, each with unique resistance curves. First things first, you need to verify engine temps with an IR gun.. Otherwise you are shooting blind.

Napa probably sold you a Std Electronics TS6, Autozone carries the Wells TU5. I bought two TU5s and then resistance tested each on the stove at various water temps. The original GM temp/ohm curve is as follows.
160F-140ohms
170F-125
180F-110
190F-100
200F-87
210F-75

Start with an IR gun at the t-sender housing. Hopefully you only have a sender issue. If its a gauge/sender issue, buy a couple of TU5s (cost $5@) and use the one closest to the std spec. If the IR gun confirms the existing gauge, then you got "other" issues.

Talisman, Thanks for the helpful info. Would I test the sending unit ohms out of the car by putting one multimeter ohm wire to the tip and the other to the main body of the sending unit?

I had a similar issue,with my sending unit. Its pretty much a crap shoot,buying one. I bought 3 before I found one that reads right,and that was the Wells TU5,at Auto Zone. I think they call it Duralast now. Other members have bought the Wells,and it didn't help. Tom Dewitt also sells sending units that are suppose to be calibrated to original specs. Like I said,a crap shoot.

Thanks 65.. At least I know I not alone in my frustration. Did you install those you bought to check them for accuracy or do the hot water/stove thing??:thumbs: Dave

I will make this statement with confidence, there is no correct answer!

There are NO correct sending units! What will work for one car will not work for another! Even my own calibration chart that I’ve used for years and have posted on my web site is wrong and will be pulled down!

I have been lucky on another forum thread where a customer recommended the sending unit that we have and it fixed his car perfect! Luck, pure luck!

I do not have enough time today to elaborate on all the reasons why I say this, I will give you a brief run down.

I can test five dash units ranging from new old stock, reproduction, and original used in great working condition. The input to required reaching fixed points on this gauge will vary! Some drastically and this is caused by the condition of the gauge.

I can also pull 10 sending units out of stock and test the output of these at different temperatures and in the odds of finding two that are exactly the same is impossible. Most of the senders tested from like manufacturers will give a pretty close output reading. When switching vendors it can go off the chart.

The gauge is not a linear gauge so introducing a fixed ohm resistor inline (on the ohms input wire from the sender) is not an option unless you only care about the temperature at one fixed point! You can dial in a temp gauge to lets say 180 by putting a resistor inline but this gauge will only read correct at 180.

On the gauges that use parallel resistance over the ground poles you can make a change in the resistance to correct the dash unit to match the sending unit in the car. (On gauges that use the resistor shut). Normally this resistor is around 90 ohms. If this is done the change to the dash unit is non linear and can correct the dash unit to match the sender across the scale as long as the sender being used will fit the bell curve of what assumed to be a correct curve (I’m not done with this yet).

In essence what will work for one car will not work for the other. Is there a solution?

Well knowing what the input ohms to your dash unit at a fixed mark is a starting point. Knowing the out put of the sender to what degree is another good starting point.

My work on this of late has centered on a 77 dash unit I’m doing for another forum customer that includes matching the dash unit to the sending unit for a crate motor engine. This also involved turning down the sending unit to the different size thread. But when we changed the parallel resistor on the back of the gauge it now functions correctly over the entire scale that matches the output of the sending unit.

I hope this makes sense! Anyone here want to add to this feel free. My goal here is to try and devise a way to for people to fix these darn gauges and to possibly create some way for you the customer to tell what is going on.

I will do a thread on this when I’m done and hopefully this will help someone down the road. What seems to work best at this point for the mid year cars is to use the IR gun and just know what temperature the car is at what mark ignoring the numbers on the face.

Willcox Inc.
18243

Thanks so much for your reply. It clears up many of the questions I was having and explains alot as I go forward with fixing this thing or at least getting the gauge to be able to indicate a true overheating problem if it occurs. I'm not as interested in a totally accurate reading as I am in just being able to tell if I'm in an emergency heat situation sometime. :thumbs: Dave

Camaros with gauges use the same sending unit as the Vette, but they also had a different unit for cars with idiot lights.You need one of the following:

Standard Brands TS-6
Wells TU-5
AC DELCO G1852
NIEHOFF TS26001
AIRTEX 1T1053

Yeap...you got it. Not a biggie. Just pick the closest wells TU5. I used both the stove top method and the oven. I baked the t-senders for 20 mins at 220F and checked the resistance top to body. I used the one closest to 70ohms. I recall on was around 90 and the other around 80ohms. So I used the 80.

Thanks guys. The NAPA unit that's reading so high is an Echlin TS6469SB.
Buns, NAPA did have one listed for the idiot light dash but this was supposed to be for the meter. I tried buying from two different AutoZone stores this morning and the kids at the computers couldn't find any temp sensors listed at all. We all know how motivated they are to help. I asked an older guy too and he was just as much help. Anyone got a part number for the AutoZone Wells TU-5 that I could go back to the store with?? Thanks. :thumbs: Dave

The Auto Zone number is the TU5.

Buns did a great write up on this and I saved it as part of our research. (Thanks Buns).

I don't know if he had this posted somewhere in a PDF or not but I saved it in PDF format. Oh, here is the link to the thread. . . I just copied the info and put it in a pdf for usage.

http://forums.corvetteforum.com/c1-a...t-problem.html

In one of the charts he listed the TU5 output as

100 – 375 ohms

180 – 145 ohms

200 – 116 ohms

In the TU5 we tested just last week we got these readings from it.

100 – 424 ohms

180 – 156 ohms

200 – 124 ohms.

So as you can see from this two of the same senders and two different settings.

We tested 4 TU5 senders in one day and none were the same! But overall the TU5 seems to work closer than anything I've found so far. This is the sender that we got the lucky hit on with the one customer mentioned in our post above.



Willcox Inc.

No,I just put them in and then used the IR gun until finally,one of the senders matched what the IR gun said what the actual temp was. Its amazing how different 3 brand new senders can read. One of the senders I bought from a vendor was 40 degrees off.

Autozone temp sensor
 

Have them look up a WT203Z or a TSU5. Those are the numbers that I have on my AutoZone Wells TU-5 box.

Dave,I just went to Autozone's web site and typed Duralast tu5 in the search box,and the sending unit came right up on the screen. Cost is $5.99. You can order it on line if you wish.

Thanks again guys. I was online to the Autozone site trying all wording and number combinations I could think of trying to look up Stratplus's part numbers he so kindly supplied and having no luck. Vette dude thanks to you for restoring some of my sanity. They call it a "switch" and not a "sender" which makes all the difference in looking it up....not that I should expect the guy in the store to know something about that terminology to find the part for me!! I'm on my way to the store now with this info you've provided. I'll let you know how it goes. Greatly appreciate you sticking by me on this!!!:thumbs: Dave

could the orig wire going from sending unit to gauge have a kink or partial ground in it. would a new wire straight from sending unit to gauge
be a good test? jim

Yes, it would. That would eliminate (or confirm) the possibility of a bad or high-resistance connection where the production wire passes through the bulkhead connector on the front of the fuse block. :thumbs:

I bought three TU 5 senders from three different Autozone stores within 20 miles of each other today. Each store only had one in stock. Two came in Duralast boxes and one in a box that says Wells. All identical in looks and made in Mexico. They all tested within a few ohms of each other and were very similar to your results:

100 degrees.......432 ohms
180 degrees.......158 ohms
200 degrees.......118 ohms

I'll install one tomorrow and see what my gauge does with it. Thanks for all your help.:thumbs: Dave