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5/2/13 9:24am - Original Message: 'Coolant Temperature Gauge Not Working'
PB2
Former Member
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Portland, OR - USA

Vette(s):
1974 roadster

Joined: 9/30/2012
Posts: 26
The coolant temperature gauge in my 74 is not working. I replaced the sender, but it did not help. The resistance from the center terminal of the sender to the block when the engine is cold is 1.37K ohms, when the engine is hot it is 0.293K ohms, does anyone have any idea if this is correct? The voltage at the sender with the engine cold is 11.01 volts, with the engine hot it is 9.55 volts. The voltage at the green wire on the back of the gauge that goes to the sender reads the same as the voltage at the sender, so I think the wire is OK. Any help would be appreciated, I am looking forward to getting it out this summer but don't like running with out a temp gauge.    

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5/2/13 12:21pm - Reply: 'Re: Coolant Temperature Gauge Not Working'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19449
Take the green wire off of the sender unit, and ground it. With the key on, the temp gauge should peg HOT.
If it does not, you either have a wiring issue, or the gauge is kaput. There shold be a small resistor bolted across the terminals of the gauge itself, and if it is bad, the gauge will not read correctly, or may not work at all.
If the gauge pegs HOT, then you have verified the wiring and the gauge, so the only other problem would be the sender.
Just to be sure, you are testing/checking the sender unit on the driver side, between the two front cylinders correct? There are two temp senders...one on the driver side for the temp gauge, and one on the passenger side for the Transmission Controlled Spark(TCS) system. Thumbs Up

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Joel Adams
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5/2/13 10:44pm - Reply: 'Re: Coolant Temperature Gauge Not Working'
PB2
Former Member
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Portland, OR - USA

Vette(s):
1974 roadster

Joined: 9/30/2012
Posts: 26
Thanks Joel
 
   I grounded the green wire at the sender on the drivers side of the block and it pegged the gauge . As you stated this would indicate that the sender is the issue. I am surprised, as it is a new sender, supposedly correct for the car. I also checked the resistance between the case of the sender and the block and it was 0 ohms, so that should not be an issue. I am going to go back to the supplier and question the application of the sender. I really appreciate having the C3 community to bounce these kind of issues off of, its really great to have all of this knowledge and support to keep the C3's going.
 
                        Thanks for your help
 
                                         Pete     


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5/3/13 7:31am - Reply: 'Re: Coolant Temperature Gauge Not Working'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19449
I have said many times, "New don't mean diddly"....LOL
How many new light bulbs have you screwed in, just to have them pop as soon as you turn them on?
Temp sending units are made for the masses, and rarely does "one size fits all" actually ring true. It's next to impossible to get a correctly calibrated one to begin with, but...you should be able to expect them to at least work some.
Part house senders may work, they may not...it's a crap shoot. Lectric Limited has about the best reputation for quality senders, correctly calibrated for the application. If a replacement sender for your non-working one  doesn't solve the problem, you might want to check into Lectric Limited's stuff.....it's a little more pricey, compared to off-the-shelf stuff from the local parts house, but the price is usually well worth it. imo.Thumbs Up


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Joel Adams
C3VR Lifetime Member #56    
My Link


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             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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5/3/13 11:50am - Reply: 'Re: Coolant Temperature Gauge Not Working'
dc502
Former Member
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Colusa, CA - USA

Vette(s):
1972 Corvette. Base 350 with hooker headers and side pipes. 265/50/15 tires on stock wheels

Joined: 1/24/2013
Posts: 15
Wilcox has a great video that will show you how to test and trouble shoot your gauge. I think there was 3 steps to it. I agree with Adam about parts house senders. I read somewhere that the generic aftermarket ones will not work. Id go to that vendor he suggested, you might find you pay more but it will work right the first time.  make sure you watch that video it really will help you pin it down.

P

|UPDATED|5/3/2013 8:50:54 AM (AZT)|/UPDATED|
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5/6/13 7:54pm - Reply: 'Re: Coolant Temperature Gauge Not Working'
PB2
Former Member
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Portland, OR - USA

Vette(s):
1974 roadster

Joined: 9/30/2012
Posts: 26
Thanks for the tip on the Wilcox site. They had exactly what I was looking for in their tech tips, the resistance range for the gauge. The sender that I bought online registers over 1000 ohms cold and never goes below 290 ohms even with the engine at operating temperature. According to the Wilcox site the gauge does not even start registering until the resistance is down to 220 ohms, at normal operating temperature it should be around 80 ohms.
 
 
             Great info
 
                           Thanks again!
        


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