Greetings Fellow C3'rs,

As a followup to my previous post:

http://forums.corvetteforum.com/c3-g...anel-size.html

I have now fitted the full frame 32" 3 core radiator with twin 12" fans. I would have thought that would keep the water temps down however a quick test drive of 10-15 kms the temp gauge was reporting 240F.

She's a new BluePrint 383 running a new Summit SMP-TS6 SWITCH - TEMPERATURE which according to Summit is application correct.
\Frustrated, this morning I purchased an IR Thermometer and obtained the following readings (while the temp gauge was showing 240F).

Top Radiator Hose (Stainless steel) - 116F
Temp Sender / Switch - 136F
Radiator Top 112F / Core 127F

What's the verdict? Sender or Temp gauge???

Feedback welcomed.

 

Sender.

The gauge is a 'generic' millivolt gauge. There is really no "calibration" per se. And, since it is giving a reading, the most likely culprit in your vehicle is the sender. To find a sender that is reasonably accurate with your car's temp gauge, I suggest that you contact Willcox (vendor here on the Forum). They have done quite a bit to understand the differences in these temp senders (by model year) and would be best suited to supply you one that may work well with your gauge.

 

 

Be sure there is no air in the system! An air lock can cause this.
Good luck.

 

to test the gauge you just unplug it from the sender and it should drop to zero then touch that connector to a ground such as the frame and it should peg out. If the gauge does this it is working as it should. Willcox is great but I got the correct sender from Lectric Limited. The generic senders resistance is not correct for our old cars. When I had the wrong sender, purchased at autozone, the gauge was way way off. A lot more than yours was. Did you leave the radiator cap off and let the car run at idle for a while so as to "burp" the cooling system?

Sully

 

Thanks for all the replies thus far.

Given it's a new radiator (and sender) I'm inclined to think it is an incorrect sender unit. Summit's technical advice service has not been overly helpful.

The IR Thermometer confirms actual temps throughout the cooling system and the variation in temps is what I would expect.

And yes the system has no airlocks.

I recall seeing a "resistance chart" for the correct sender in the Vette, but cannot source that info again. If it was available, I could check the resistance values at given temps.

So, what's the best method to determine which is the correct sender for the gauge?

 

220* = 70 ohms
200* = 90
160* = 140
120* = 250

 

"Lectric Limited" carries properly calibrated send units, assuming you're using a factory gauge. I'm running a 450 hp 383 in my 61 with a stock radiator from Dewitt's and a stock clutch fan. It runs 180 all day. You probably didn't need all the fancy fans. Good luck

 

Thanks. Exactly what I was in need of.

It's 5.30am at present and a bit too early to fire up the beast - (it would wake the neighbors) so I;ll have to wait a few hours to test mine.

capevettes, thanks for your feedback as well. Reassuring to know your results. Once I determine what my sending is doing, I'll source from your supplier, assuming they ship to Oz.

Now I'm patiently waiting for sunrise

 

temp senders made in the aftermarket vary greatly. Good advice on working with Wilcox. Just to be safe even when the car gauge says <210, i installed a separate temp gauge to compare. Maybe I am just the guy that uses a belt and suspenders too.

 

I've monitored the temp (gauge & sender) and resistance. The following is an approximation given I was bouncing between gauge, IR thermometer and multimeter:

Gauge* Sender* ohms

160 = 120 = 43

210 = 112 = 40

250 = 130 = 35

This is considerably different to the table provided by petes74ttop.

Looks like the culprit is the sender.

I've been in touch with Summit again to see what the specs are of the sender provided by them.

I've also been in touch with Lectric Limited as their shopping cart reports a freight cost to Oz exceeding $400 waiting on a reply with a sensible and realistic cost.

Thanks for all the input...

 

Below is the test chart we have used for years when setting needles on gauges and testing working units for 1968-1974. The input readings were created by taking a large sample of original NOS gauges and inputting ohm’s until the gauges read at a fixed point. This test was repeated with dozens of gauges to verify accuracy and has been something I've actually kept only in my shop until about a year ago. The inputs are not the same for say a… 65 76 or any other year. (Ignore the test codes in this chart.. they are the setting combo's for each **** on our tester so that we may set the output quickly).

Can the dash units be calibrated? Actually yes they can and it is a royal pain in the rear end right now. Calibration can be done and this has been discussed for a long time in some other threads Roger and I participated in. Roger tried to get me to make this for the longest time so I added it to the “To Do” list…. We’ll the time has come because we started working on this project right after the low fuel warning modules were completed. You’ll have to be patient for this one... We’re doing three things with this project… One is the make a workable resistor for the back of the gauges for both 1968-1977 and 1977-1982 (different resistor), and one is to make a working pot for the back of the gauges for self calibration.

Senders.. I sell them.. I hate them all…

I've tested sending units until I'm blue in the face from ALL suppliers. Every now and then you'll get one that will be close... But for the most part none of them work correctly. I do have another batch of senders in from yet another source but I fear they will replay the same numbers as the other senders. What you’ll find is a sender that is not capable of reaching 51-65 or for that matter 79 ohms of out put.. most of the newer senders will max out at around 90-100 ohms max. Knowing this will allow you to boil any new sender you get and instantly take an ohms reading. If you find one boiling at or around 79 ohms.. you have found a winner..

The issue is the thermister disc located inside the sender combined with the lack of oil in the senders. I’ve tested and I’ve cut open one from each vendor I’ve purchased from and to date I’ve not found one drop of oil in any of them.

My suggestion for now.. is to always to seek out an original sender working or not!

I'm thinking about doing a video on how to repair these but it is quite simple. Most of the original senders that malfunction have lost the oil from inside and corrode. You can remove the top of the sending unit if you are careful. I have a metal lathe here that I chuck them up in and actually cut off the end of the crimped brass. Once I have the end off I then remove the top, pull out the paper tube (you’ll find one inside), remove the spring and in the very bottom you’ll find what is called a thermister. This is the resistance disc that causes the senders to work. Clean all parts and refill the sender with oil. Epoxy the top back in place with your favorite stuff and you’ll find your original sender, while not looking so hot will work correctly again.

 

BigBadBorry...

Are you sure that your sender unit is for an early C3 Corvette? Some other Chevy's had a sender/switch that turned on a "TEMP" light when the coolant got too hot. Yours doesn't appear to change resistance with temperature. I'm thinking it's not the correct item.

 

This is the potential culprit:

http://www.summitracing.com/parts/smp-ts6

and this was recommended by Summit...

 

That is a Wells TU5 and it will not work worth a hoot.. It might be boxed in a standard products box or available in many other forms.. but it won't work.. It will not reach the needed lower ohm's points.. and it has been known to go haywire when it gets to the lower ohms area. (or around 200 deg). Actually it say's Standard.. I didn't see that. But Standard and Wells use the same supplier on this product. Again.. you may get one close one out of 100 but the odds are not in your favor.

 

Are you sure about the sender output.. You must remove the wire from the sender when taking the reading. If you tested with the wire on the sender it would account for the low ohms readings. Pull the wire and test again when the gauge hits fixed points.

Willcox

 

Thanks to everybody who contributed to the pool of knowledge regarding this problem. It was a learning experience for me.

In the end, I went back to the original 350 that was in storage, removed the sender, cleaned it up on the buff (looks all shiny and brand new now) and installed into the 383.

I ran the engine for some time, then proceeded with a 10-15km drive. The IR thermometer reports a temperature within 5 degrees of the gauge now!!!

Big smiles all round

Thanks again for all the input and advice, it was certainly appreciated.