Hi all, I have a problem choosing the right coolant temperature sensor with 3/8" thread that could work with the original '74 instrument.
When I had the iron 882 heads, i fitted a standard 1/2" thread sending unit that @200°F the ohmic value was about 100R.
For my new aluminum heads I bought the FOUR SEASONS36401 that is compatible with the 82 chevy corvette. The problem is that @200°F the homic value is about 200R so the instrument, obviously doesn't work.
Could you recomend a sensor to me that is 3/8" and about 100R@200°F?
Thank you!

 

https://www.corvettecentral.com/c3-6...r%26count%3d18

 

Wilcox Corvette makes one for that year in 3/8 npt.

 

I thought to use a trimmer in parallel to the actual sending unit to center the gauge at the right temperature. But the problem is that the reading is not longer linear.
I also thinked to use an op amp to condition the signal but if is possible I prefer to find a "ready to go" solution...

 

I saw it, but I think that 79$ + shipping + customs fees it's like a robbery... I'm sure that there is another sending unit that can solve the problem. The fact is that the producers not always give a datasheet with the curve of ohms/resistance.

 

Uhhhh ... how 'bout opening up your new heads to fit your old, larger sending unit ... drill & tap ?

Also, maybe you have a new intake manifold too ? Maybe it has a null port that fits your old sender?

 

This would have been the best solution. But (my mistake) thinking that the sending unit that i bought worked, I installed it and now the engine is closed...

In my intake edelbrok 2701 I have a 1/2 port. But a temperature sender placed there, will interfere with the water hose

 

Water neck/thermostat housing ... not expensive ... several years have ports in them ... some should fit your old sender

 

Good idea!

 

I paid the almost 100 bucks for that one on my build, they actually build them upon payment, took almost 6 weeks to receive mine. It works well though

 

oVoSanto
Just get ahold of willcox and order the sender they recommend for your vehicle, and also order the temp gauge adjustment kit. I works just wonderfully. I put up with my innaccurate gauge for decades and it was so easy to fix.

Here is my story. Just make it easy on yourself. https://www.corvetteforum.com/forums...-question.html

 

We make the senders for all cars 1963-1977 in a 3/8 thread.

https://willcoxcorvette.com/corvette...79-3-8-npt-new

It won't matter what sender you purchase, all the new senders are wrong in their readings. So once you have the proper style sender from the link above, purchase the adjustable resistor that installs on the back of the temperature gauge and you can dial the gauge in to match the sender.

https://willcoxcorvette.com/corvette...resistor-68-76

There is a video at that link that will show you how to install it once the gauge is out of the car.

Willcox

 

Thank you!

 

I have a bit more time right now than I had in my last post. I’ll save this post so that I don’t have to do it again later on down the road.

It matters not what sender brand you purchase for your car, they all read wrong in relation to the dash unit and that includes the so called “correct” sending units.

How do we know this? We purchased every brand of sender being made and tested them for hours on end. We also have tested in great detail what is called the expected input for each and every dash unit for their expected inputs at each temperature and most of these expected inputs can be found on our tech site. We have one page that I’ll post later because the PDF is not loading correctly right now but use the link below until I can repair the file. What is nice is that we did this using on original NOS gauges and original working used gauges before they all dried up. The scales we published for the inputs to the dash unit and those that we have used for years to calibrate original gauges that have been repair in our shop.

http://repairs.willcoxcorvette.com/?...perature+gauge

So what went wrong? What went wrong was in or about 1992 GM sent the production of senders down the boarder and when they made the senders they goofed on what is called the”thermister”. This is a resistor that is located inside the actual gauge and what controls the output of the sender. Once GM made them wrong the aftermarket people followed suit.

Now we are aware that the so called “correct” senders have inside of them what is missing from the other senders and that would be oil… Well we purchased and cut one apart and found no oil. Does this make a difference? No. The thermister is going to read what it is going to read with or without oil. What the oil does is keep the contacts from corroding inside and if you really search hard on our tech page you will see where we took an original sender, cut it apart and cleaned all the contacts. We then filled this sender with oil and fabricated a new top for it. The sender works and still does to this day as originally designed.

So I guess as far as senders go, it’s always best to try to find an original sender and if not, the purchase the adjustable resistor for the back side of your gauge.

Another question I get all the time is “can you install resistance inline” Yes you can do this and make changes to the reading but when you do this the dash unit will only read correctly at on given point and the rest of the scale goes out the window because the dash unit and the sender are both non linear gauges.

What the adjustable resistor allows you to do is make a linear change in a non linear gauge and doing this allows you to calibrate the dash unit to match your new sender.

IMHO,

Willcox
18243

 

This is really really useful.


Surely modifying the instrument is the cleanest solution.


In my situation, where the sender @200°F have 200R and when the expected resistance for the instrument is 100R for a true reading, the correct thing is to put a 200R resistor in parallel to the sending unit. Obviuosly is lost the linearity of the reading but at least you are centered at 200°F and is visible an overheating. I remark that this is a rough solution.


Said that, I'll go with purchasing the back resistor of the instrument that you propose.

Thank you for the precious support!

 

Hi everyone! After some time I resume this 3D to tell you what I did. The first workaround was to take a sending unit for '82 corvettes by paralleling a 180R resistor. More or less I had an indication of the temperature but obviously the linearity was lost.
There were 2 ways to definitively solve the problem.
1) change the resistance behind the little instrument. But will to disassemble the instrument = zero.
2) swap the NTC (Negative Temperature Coefficient: resistance that decreases with increasing temperature) of a 3/8 "sending unit with that of a 1/2" sending unit suitable for my '74.
I choosed the 2nd!



The first thing to do is to remove the collar that holds the connector in place with its black plastic spacer. You have to be very careful when you are about to open it because the spring that acts as a contact is very strong and compressed. Could make fly away the sensor, which is the small pill (marked in green and red):



Having filed away the collar that holds the connector, I had to seal the sensor with two-component epoxy. To reassemble it, I recommend that you first put the cardboard tube that acts as an insulator, insert the ntc and the brass support that optimize the contact (not visible above). Then I put a small amount of glue on the inside edge of the cylinder, And the spring. Then I closed with the plastic support that includes the connector. It only takes a few minutes for optimal adhesion.



739 ohms @ 16°C. Good!



At this point I had to ensure a perfect mechanical seal. I drilled 6 holes (1.5mm) inclined inwards and for maximum adhesion I scrached irregularry the surface of the device where I would have poured more resin:



This is the final result:




And here installed in the head:




Basically I spent a nice afternoon and solved the problem!

 

epoxy inf?
brand,& type
great job

 

General Chem RV47. It has an excellent resistance to mechanical and thermal stresses and good adhesion even to supports with very different coefficient of thermal expansion.
I'ts a professional product, I'm not sure that you can find it easily. But you can use another epoxy system like the Electrolube ER2224.
https://electrolube.com/wp-content/u...224_vdirxh.pdf

 

 

I mounted mine in the intake... works the same and its hidden under my rad hose. I actually have a different digital oil temp gauge with a sensor in a head and the two gauges are typically within a degree of each other.