0Willcox Corvette

The pictures to this write up were hosted on our old site, when we moved it over to the new site it changed the links and the pictures go poof.
However, this entire write up is still available to anyone at this link and it does include the pictures.

http://repairs.willcoxcorvette.com/1...ender-cleaned/

So many times we are asked if there is a way to repair the temperature sending units. The answer is yes... Will they look 100 percent, NO! But they can be made to function like there were new again. I did a write up about this on the site this past weekend and thought I would share some of it with you all.

This is not something a novice should try, let alone the fact that you need access to a lathe. ... But here we go.

Below you see an original temperature sending unit. It has been cleaned before we begin our journey.


53-82 Temperature Sending Unit Rebuild/Repair
Your temperature sending unit failed and after replacement you found the dash gauge isn't working properly. Failure has been the consistent experience with both the current reproduction and all replacement sending units. Below we've illustrated how we can repair the original units and possibly give you some insight on how the sender works. This is not something most will be able to do at home since a lathe is required.

So we start out with a original GM sending unit, p/n 1513321. For years we sold this part without any issue. For some reason around 1992 Gm moved production of this to Mexico and it’s my belief that’s when the problems started.

We begin by chucking the sending unit in our lathe to remove the crimping portion of the sender. This is what holds the sending unit together.



Once the cap was removed all the internal parts were exposed… and the oil leaked out… Oil.. you read correctly. While once believed to be one of the major causes for inaccurate sending units… it’s not. As you will see below, the reproduction senders do not have oil in them. I've cut every brand apart from BW, Standard, and all the reproductions… I’ve never found one with oil inside.


Now if you look closely at the sending unit in you’ll see a spring inside. If you look closer you’ll see the corrosion on top of the spring which ultimately leads to the failure of this sending unit. This spring transfers the resistance to the top electrode.


If you look at the top after it is cut out you’ll see on the back side the electrode that actually sits on top of the spring in the sending unit. Unfortunately, the original was damaged by accident, but and the only difference between the donor top that I used, and the original was the way the seal was made. Replacement and reproductions actually have a better top cap because the seal is made into the top. If you look at the left most picture you can see the red seal behind it.

Once you have the cap off, you'll expose the other parts shown below.


The thermistor is a type of resistor that changes resistance based on temperature. The style of thermistor used in today’s sending units are way different than those used in the old GM sending units. Commonly the new senders are not capable of sending an ohms reading lower than 100 ohms and the scales are incorrect.

So now what? You clean all the parts and re-assemble the unit. We’ll show you how we do it.


We start out by cutting the top down in the lathe again. If you look above, the middle cap is un-cut, the one on the right has been cut down We remove about 1/2 the outer lip before we begin. Make sure you don't remove to much, the cap must be wider than the diameter of the case bore or you've wasted your cap. It has to be this large to seal.

Before you assemble, you’ll need to scuff the area’s shown with 180 grit sand paper. We’ll be using epoxy glue to re-assemble and you want it to have something to bite too.


Clean the inside of the case making sure there is no debris or corrosion in the bottom of it.

A suitable seal must be found and placed under the cap as shown below. I’ve never put one back together without putting a seal inside. The seal should extend to the edge of the cap only and when installed look similar to the picture below. Just make a hole for the electrode and trim around the edge.


Once you have the case scuffed, the tube and thermistor and spring should be installed, you’ll then want to add oil. Put enough inside to reach just barely below the top of the bore keeping the sender level at all times. (no oil should come out of the case and into the scuffed bonding area) Place the cap on top, center it, and then clamp it! (Again... being careful to keep it level). While clamped you then us PC7 two part epoxy to hold the top together. You have to work the epoxy down around the cap. Shown below.



Once our epoxy is dry, We then put the sender back in the lathe and dress the epoxy down to look as close to the original cap as possible then sanding a bit to smooth it out.

We then paint the top (the epoxy is gray) with heat resistant paint and we are done. The finished product.. A sender that looks close, but functions as original.



I'm sure I made some typo's... so please point them out if you find any.

Questions welcome... and remember, I did say if you dare.

Ernie

MrJlr

That's very cool!

AirBusPilot

My car must have one of those new temp sensors, as the needle will barely get off the first mark when warm.

0Willcox Corvette

Either your sender is bad, you have a wire broken or the wire is off the sender. A gauge that reads cold all the time is missing ohms input. Go to the sender and pull the wire from it... ground that wire to the engine and with the key on see if the gauge goes to full hot!

If it does you've done the following:
You've confirmed the wire from the gauge to the sender is good
You've confirmed the gauge has good power and ground.
You've confirmed the sender is the issue.

If it doesn't.. you pull the center cluster out of the car and take a look at the gauge, and gauge wiring. There are more test once you get to this point.

Testing a 68-82 Temperature Gauge -or- What your non working gauge can tell you!

AirBusPilot

Wow, thanks. Based on the video, it appears my guage may be missing the insulating washer, as it hovers around the 100* mark, barely moving above it when hot. Do you guys sell that washer? Or is it something I can probably fab up?

0Willcox Corvette

It very well may be.. If your gauge is pointing exactly like the one in the picture below, I'd almost bet money it's your problem.

If you need to remove the center cluster, here are directions that will help you.

Corvette Center Gauge Bezel Install 68-76
http://willcoxcorvette.com/repairand...lp.php?hID=112 <-- Click on supporting document

AirBusPilot

Ok, did the wire test and the gauge pegged. Just to confirm, that means the sender is the issue?

0Willcox Corvette

Do you have an old flasher laying around anywhere? If you do.. plug the temperature sender wire into one flasher terminal, and then ground out the other end of the flasher to the block (old school tester).

A flasher generally has around 50 ohms.. so knowing this your gauge should to to around 250 on the face. When you tested it by grounding out the ohms wire it went way past the numbers to around the 3 o'clock position.. so doing this will give you a good idea the gauge is working.

If it does this then by all means you should look for a sender.

AirBusPilot

Thanks!

0Willcox Corvette

If you don't have a flasher.. you have a 71.. there is one located right under the right hand vent ball behind the dash.. rob that one and test away..

labhound

Hmm, maybe I should keep my old one, it worked till I broke off the connector, hopefully the one I just got from Willcox will work good...

AirBusPilot

I will give that a try, thanks!

FireballXL5

Awesome write-ups man! Much appreciated ! Ordered a temp sending unit the other day , hope/plan to install it tomorrow... Hope it reads accurate when I'm finished... A little worried over the statement the new ones don't like reading below 100ohms... But I won't know til I try to replace it ... Time... And temperature will tell... THANKS again!

AirBusPilot

Just tried that test and the gauge swung to 250, like you said.

Time to order a new sending unit. Thanks again!

0Willcox Corvette

You can use a flasher to test Fuel gauge, Oil pressure Gauge, and Temp Gauge. If you purchase a new one.... no way would I toss the old one. What you should do is remove the sender, clean both the contact and the threads and test for ohms. A cold sender should have 600 or more ohms. If you get a reading after it's clean re-install it by putting Teflon tape, two turns on the first couple of threads only. Teflon is not a sealant, it is a lubricant to assist the brass threads in seating.

Odds are against you that a new one will work correctly..

Willcox

Griff2002

Thanks for posting this very interesting information. I have developed an intermittent problem with my temperature reading. As the car warms up, the temperature gauge reads appropriately. However after a few minutes the gauge starts to flip back and forth rapidly and then settles all the way to the left. Resistance between the terminal and the block at about 75 degrees is 564 ohms which I think is about right. I checked with the car warm and had a difficult time getting a good reading, but eventually got a reading of 140 ohms which seemed reasonable as the car had started cooling down. The resistance between the wire that attaches to the sensor and the block is 60 ohms.

So I am wondering if my sensor is bad or if the problem is with the gauge?

FireballXL5

Struck out... The sending units I tried to order were not the correct ones... The one I thought was for the water temp, they had listed for the oil temp... So I returned it for now so I can get the right ones through you guys...

The other one had a different style plug in also, so returned that... Took pics of the part numbers and sending units just for future reference of what NOT to order... But perhaps I'll be best to pull mine to get part numbers off them...

Or hopefully pull mine, clean em, test em, and hope for a little corvette miracle that the oil temp one can come back to life...

FireballXL5

Losing connection at temp in the sending unit wire ? Full left (like mine) is lack of signal... If you're confident that the connection at the motor is good and tight... Could be the connection at the gauge? Or perhaps the wire running between both has a rub through the casing somewhere and could ground out? Would that provide the symptom?

FireballXL5

This is what they had listed as my oil temp sender... But mine has two prongs coming out of it...

FireballXL5

This is what they had listed as water temp sending unit... But mine has a single spade clip similar to the first picture... Not like this plug in.. Need to investigate further into what I actually have in my 383 block...