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i would like to know if my sensor or my gauge is bad. when i take the sensor wire off and turn switch on it stays at 0. when i ground the sensor wire,it pegs it all the way hot. has not worked since i owned the car.it's time to get all my gauges working.i've used meters before but when it comes to ohm's i get a little lost but i'm good on directions. looks good on the back where the resistor is and the fiber washers look good. thanks
That's what it's supposed to do. The gauge is reading as it should in an open and a shorted condition. What does the sensor read (in ohms) from the top connection to the engine when it's up to temp? And describe what you mean by gauge not working. Not accurate? No movement? Too much movement?
Last edited by 65GGvert; Mar 18, 2016 at 05:05 PM.
have not made that check yet.no movement at all when up to temp.i'll be back at it this weekend and make that check.set meter to ohm's and one point on sensor wire terminal and the black one on the block?
Originally Posted by 65GGvert
That's what it's supposed to do. The gauge is reading as it should in an open and a shorted condition. What does the sensor read (in ohms) from the top connection to the engine when it's up to temp? And describe what you mean by gauge not working. Not accurate? No movement? Too much movement?
have not made that check yet.no movement at all when up to temp.i'll be back at it this weekend and make that check.set meter to ohm's and one point on sensor wire terminal and the black one on the block?
Yes, and the warmer the car gets, the lower the resistance will read. I've seen a chart on the forum with resistances at different temperatures, but I don't have it available right now. I'm thinking at 180 you should read about 120 ohms, but I'll look later for that chart. At room temp, I think it reads over 600 ohms. If you're getting an open circuit or infinite ohms, or very high ohms, the sensor is not working, if you have the meter connected properly.
Here's one from an early 70's Olds, it should be the same, but it will give you an idea what you're looking for. If your's doesn't move at all, it must be open. I would suggest checking wiring or the firewall connector, except that you said when you ground the green wire it reads full hot, so that should be good.
I just went through trying to sort out what I thought was a component problem on my 68. I had taken the interior apart years ago and when putting it back together I relied on the GM schematic. Make sure the green wire (gage input) is on the top and the red (12V) is on the bottom of your pigtail. Hugh
thanks for the chart. i have a mechanical gauge hooked up under the hood along with a tach. vacuum and oil pres.and volt meter. i kind of use the engine for a distributor machine to set up a timing curve.today i'll check the sensor at room temp and probably remove it if it does measure up to snuff. i feel pretty confident on how to measure ohm's,just never had to in the past.i'll keep you informed on progress. i know this has been covered many times but i have not owned this vette that long (about 6 years).
Originally Posted by 65GGvert
Here's one from an early 70's Olds, it should be the same, but it will give you an idea what you're looking for. If your's doesn't move at all, it must be open. I would suggest checking wiring or the firewall connector, except that you said when you ground the green wire it reads full hot, so that should be good.
thanks for the reply. i'll probably check everything out while i have the instrument panel out. i would like to get it right before i reassemble. it's kind of a pita to work with.
Originally Posted by hugh9222
I just went through trying to sort out what I thought was a component problem on my 68. I had taken the interior apart years ago and when putting it back together I relied on the GM schematic. Make sure the green wire (gage input) is on the top and the red (12V) is on the bottom of your pigtail. Hugh
just went out to the garage and did an ohm measurement.i get a consistent 615 on my ohm meter. i'll call the temp in my garage at about 40 degres .thats where i get confused on the decimal points on the meter,but these are the three numbers i get consistently.when i move the range,sometimes i get nothing. i'll have to brush up a little on how to read it better. drained the block for now.
Originally Posted by 65GGvert
Here's one from an early 70's Olds, it should be the same, but it will give you an idea what you're looking for. If your's doesn't move at all, it must be open. I would suggest checking wiring or the firewall connector, except that you said when you ground the green wire it reads full hot, so that should be good.
saw this on the forum so i made one.soldered a 100 ohm resistor on a piece of wire with a clip on one end and a male spade terminal on the other. hooked the green sender wire on the spade end and grounded the other and turned the switch on and the temp needle went to the first mark on the gauge. outside temp is about 45 now here. really do not know what that means.
Originally Posted by 65GGvert
Here's one from an early 70's Olds, it should be the same, but it will give you an idea what you're looking for. If your's doesn't move at all, it must be open. I would suggest checking wiring or the firewall connector, except that you said when you ground the green wire it reads full hot, so that should be good.
That means your gauge is working. Temperature of the room or anything else doesn't matter when you're jumping resistance to ground. The only thing temp affects is the resistance of the sender, which is out of the circuit when you do that.
Last edited by 65GGvert; Mar 19, 2016 at 08:02 PM.
with the gauge working that leaves the sender as the weak link.any thoughts on a good sender? seems like a good one is hard to find is what i hear. thanks.
Originally Posted by 65GGvert
That means your gauge is working. Temperature of the room or anything else doesn't matter when you're jumping resistance to ground. The only thing temp affects is the resistance of the sender, which is out of the circuit when you do that.
Since you've made the needle on the gauge move....it's NOT the gauge. And your 'testing' has verified that. You need a new sender unit. But, don't put teflon tape on the threads. The electrical connection for 'ground' is between the sender threads and the engine block. If electricity can't flow between them, you will get NO signal to the gauge.
thanks for the reply,i'll remove the sensor today and if i cannot repair it i'll try the bwd#203 boil it and test it.
Originally Posted by 7T1vette
Since you've made the needle on the gauge move....it's NOT the gauge. And your 'testing' has verified that. You need a new sender unit. But, don't put teflon tape on the threads. The electrical connection for 'ground' is between the sender threads and the engine block. If electricity can't flow between them, you will get NO signal to the gauge.
I'm not sure where that chart above is from but the correct expected values are listed on the picture above I posted. The values I posted above are the values we use when calibrating a temperature gauge and were taken from multiple samples both NOS and used original working gauges years ago. I've used that scale for probably over 20 years. The test code in the chart is in conjunction with our potentiometer which has multiple ***** and settings so each test code is a **** being turned to a fixed position. (Translation is the test code us useless to you guys).
Willcox
Last edited by Willcox Corvette; Mar 20, 2016 at 07:14 PM.
temp. gauge or sender 71
