'67 SB temp sender replacement question...

[PTighe]

My old brass temperature sender, which is screwed into the intake always worked OK; the temp gauge in the car always read about 180 degrees. Recently I replaced it with an identical looking sender from Zip. The reason I replaced it was simply because the old one was so ratty looking.

Now with the new sender installed, I'm getting a constant 200-210 degree reading on the temp gauge in the car. I don't think the engine is really 210 because I haven't done anything to the engine or cooling system which would cause this big a fluctuation. Anyone know what the deal is on this? Are the newer temp sender units calibrated for a higher temperature? Any info appreciated.:confused

 

[bradfordsvettes]

the new replacements are not calibrated the same. clean up the old one and use it. the only trick you could do is add a resister in line to trick the gage to read correctlyoff the new sender but don't know what the value would be off the top of my head steve

 

[vigman]

Most electrical components...

Are built with a 10-20% tolerance in automotive.. and the makers want to make em generic as possible so 25% might be considered acceptable.

We're talking the resistance value between 180 & 200...20 degrees.. which will be maybe 20 ohms diff HIGHER.... When you short the sender out ( zero ohms ) you go MAX heat on the gauge and a open circut ( high ohms ) it shows nothing.

I would go to radio shack and get a 100 ohm pot... wire it in series with your sender... get the engine warm and put a thermometer in the coolant res... take a reading and twist the pot to match... then replace the pot with a fixed value resistor.

You actually don't know which one is correct ( based on the info in this post)..you LIKE the lower reading better though.. this is a way to actually know the temp vs gauge reading.

Yeah it's a pain..but it's the correct way to do it..otherwise it's hit & miss.

eg on an 88 sender
75 ohms=hot/MAX
1500 ohms= cold/off scale

The sender on my 65 motor ( new ) 720 ohms stone cold!

The 73 shop manual has NO spec given!

So this requires MORE research!



Vig!

 

[PTighe]

Thanks for the advice guys...sounds like I'm stuck with a search and destroy mission, since I threw the old one out! :duh

Guess I'll have to go to Radio Shack or buy an NOS sender on Ebay for $500. :L

 

[vigman]

DOH

I hate that when I do that!

I have to find my orig intake.. that had a sender in it ( but it was for a Camaro 68)

BUT it should be close.

Vig!

 

[IH2LOSE]

What type of sealent did you use?

You are not supposed to use sealent because the sealent prevents it from making 100% contact.
I used 1 drop of leak lock (used in the air condition feild) mine read almost excact from a lazer thermometer off the top of the themostat housing .I purchased a used one because I had an aftermarket one that was also reading TOO HIGH by about 20 to 30 degrees

 

[vigman]

AH HAH

So the truth arises from the experience of the masses.....


Vig~

 

[ChuckG]

It's a VERY common problem with the "new" senders. They read 20-30 degrees too high. The solution? Spend the "big bux" and buy a NOS model, look for a nice used one at a flea market, "wire" a resistor in circuit to compensate, or try the cheap solution.

The cheap solution? I believe NAPA has a sender that will work. Go to www.ncrs.org Point and click your way to the Discussion Board, and then search the archives. I'm fairly sure there is a cheap "aftermarket" solution that has been discussed there. It won't be AC Delco, or have the correct "markings" if judging is your "bag". I believe that Fred Oliva in Florida actually makes and calibrates "correct" AC Delco senders.

Two "warnings".....first, as others have said, NEVER use thread sealant on a temp sender, and second, if you go the used "flea market route, be aware that you need a sender for a gauge system, not for an "idiot" light system.

Gauge senders have variable resistance that varies with the temperature, whereas "idiot light" senders don't vary. When it gets to the overheating point, they go on. Your gauge won't work with an idiot light sender. AND....NEVER throw out an old Corvette part, no matter how "crummy" it is. Hope this helps. Chuck

 

[PTighe]

Thanks Ih2 and Chuck, no I didn't use sealant on the sender threads but I did wrap a couple loops of teflon tape around it. If I'm correct the threads usually pop through the tape and it makes a good connection, since the temp gauge does work.

I think my first stop will be Napa to see what the senders look like, if that doesn't work out, it won't be a big deal to wire in a 750 ohm resistor under the dash. I have a new Lectric Limited harness in the engine bay which is still under warranty, so I don't dare hack that up.

 

[IH2LOSE]

pj67

teflon tape has the same insulating properties as the sealent does remove the tape

 

[vigman]

Guys 2 points to remember

1) The sender threads are pipe threads so they will go metal to metal IF enough torque has been put on the adaptor/sender.

2) IF there was to much insulation used on the sender you would get NO reading... it's REALLY hard to get just 10 ohms of resistance from an errant piece of teflon tape..or Super Blue Goo!

And in this case MORE resistance would be better....

So where did the magic 750 ohm value come from?



Vig!

 

[PTighe]

Re: Guys 2 points to remember

1) The sender threads are pipe threads so they will go metal to metal IF enough torque has been put on the adaptor/sender.

2) IF there was to much insulation used on the sender you would get NO reading... it's REALLY hard to get just 10 ohms of resistance from an errant piece of teflon tape..or Super Blue Goo!

And in this case MORE resistance would be better....

So where did the magic 750 ohm value come from?
Vig!

Vig, I misread your first post above, I thought you said you had a 750 ohm resistor in your '65. What I'd like to do is just disconnect the lead at the sender on the intake and use a jumper lead to hook an inline resistor to the "signal" end of the sender, that way I don't have to cut any wires in the beginning and it's a lot easier than laying under the dash.

I already have a potentiometer. Since this seems to be a widespread problem, many people probably have already installed the correct value resistor. Would you or anyone else have a ballpark estimate of what value resistor I would need to lower the temp gauge from 210 down to 180 again? Otherwise, I think it would just be hit or miss, because right now I can't take the car out on the road. I'm not an EE, otherwise, I could probably figure this all out at a desk with a calculator and a circuit theory book! Thanks :eyerole

 

[WayneC]

In past posts it has been said that an AutoZone temp sender (Wells TU5... just ask for one that fits your 19xxx Corvette) will show temp within about 5 degrees of accurate. I haven't tried one. Autozone is a chain parts store, dunno if they're nationwide.

 

[PTighe]

In past posts it has been said that an AutoZone temp sender (Wells TU5... just ask for one that fits your 19xxx Corvette) will show temp within about 5 degrees of accurate. I haven't tried one. Autozone is a chain parts store, dunno if they're nationwide.

Thanks Wayne, I always try the easiest solution first. Right now there is no coolant in the engine, so it will be easy to take out the sender. There is an Auto Zone close by, so I will make a stop there if I can ever dig out of this snow!

 

[vigman]

What I ment was

The sender in my 65 engine read's 750 ohms from the tip to the case COLD...

BTW the 64 book has no spec on the sender!


Vig!

 

[PTighe]

I've been doing some reasearch on this problem and found out that Long Island Corvette Supply has new recalibrated senders which will work for 63-67 Vettes.They are a licensed GM Restoration Vendor and I was told they are identical to the original. For $30, I'm going to order one tomorrow, sounds like the easiest route.

I've been buying parts from them for years and have never had a problem. :bang

 

[MidShark]

I just received a new Corvette Central 63-67 catalog and under "new products" they list "Temperature Sender With Correct AC Delco-Made in USA Markings" Correct Calibration $19.95
Part # is 301083

Dick