Temp gauge
Thread Starter
Instructor
Joined: Jan 2013
Posts: 155
Likes: 2
From: Naples Florida
Temp gauge
How can I test the temp gauge. I am concerned about letting the car run very long. Just seems it runs hot. Just repaired the carbureted, the heat gasket had portions burnt out. Just purchased, even thought matching numbers and original, bubba was there.
Help
Help
Burning Brakes
Joined: Jan 2006
Posts: 1,073
Likes: 331
From: Clear Lake Shores Texas
2016 C3 of Year Finalist
Do you have an infrared thermometer you could use to check the temperature of the water outlet on the intake manifold? That is the easiest way I know of.
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
Wilcox has a write up on this subject. The basic problem is replacement sending units don't give the correct resistance (ohms) for the gauge to read correctly. He has documented the different ohms reading for various temps for the gauge to be accurate.
But the easiest way to verify your temp gauge is as Dan 1495 suggested to buy an infrared thermometer. Harbor Freight has them pretty reasonable. When you know what temp the engine is actually running, you can then evaluate the accuracy of the tamp gauge.
Pete
But the easiest way to verify your temp gauge is as Dan 1495 suggested to buy an infrared thermometer. Harbor Freight has them pretty reasonable. When you know what temp the engine is actually running, you can then evaluate the accuracy of the tamp gauge.
Pete
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
Wilcox has a write up on this subject. The basic problem is replacement sending units don't give the correct resistance (ohms) for the gauge to read correctly. He has documented the different ohms reading for various temps for the gauge to be accurate.
But the easiest way to verify your temp gauge is as Dan 1495 suggested to buy an infrared thermometer. Harbor Freight has them pretty reasonable. When you know what temp the engine is actually running, you can then evaluate the accuracy of the tamp gauge.
Pete
But the easiest way to verify your temp gauge is as Dan 1495 suggested to buy an infrared thermometer. Harbor Freight has them pretty reasonable. When you know what temp the engine is actually running, you can then evaluate the accuracy of the tamp gauge.
Pete
Advanced
Joined: Oct 2010
Posts: 80
Likes: 2
From: near Nuremberg Bavaria
- The water outlet is NOT where the temp sensor sits; That's in the driver side cylinder head (at least on a '70 LS5). Readings will not be directly comparable...
- Measuring metallic surfaces with an IR gun is, I believe, difficult. Has to do with the emission coefficients of different materials; Better / more expensive IR guns have an adjustment for that.
- Also, IR guns measure the temperature of a certain area, the size of which depends on the distance between the gun and the object being measured. The laser dot used to target the gun is somewhat misleading in this respect.
Anyone care to comment, esp. on #2 & #3?
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,595
Likes: 7,043
From: New Or-leens Loo-z-anna
If you are that unsure of the in-dashtemp gauge, buy an inexpensive $25 aftermarket gauge that has the direct (copper tube with bulb) reading to compare with your in-dash gauge---they generally come with threaded adapters to fit your engine.
They're not rocket-science gauges, but will get within a few degrees of the actual temperature and are good for temporary testing....also test your engine thermostat opening-temp in a pot of heating water on the kitchen stove with a cooking thermometer....then you will have two reference points to get an idea of how accurate your in-dash gauge is without dropping a c-note on a decent IR gun (unless you're concerned about exhaust temps also--but that's another can of worms this rookie won't open)
They're not rocket-science gauges, but will get within a few degrees of the actual temperature and are good for temporary testing....also test your engine thermostat opening-temp in a pot of heating water on the kitchen stove with a cooking thermometer....then you will have two reference points to get an idea of how accurate your in-dash gauge is without dropping a c-note on a decent IR gun (unless you're concerned about exhaust temps also--but that's another can of worms this rookie won't open)
Drifting
Joined: Jul 2008
Posts: 1,873
Likes: 27
From: Sonora CA
While I have gone down that path myself, three things keep me worried with this approach:
Anyone care to comment, esp. on #2 & #3?
- The water outlet is NOT where the temp sensor sits; That's in the driver side cylinder head (at least on a '70 LS5). Readings will not be directly comparable...
- Measuring metallic surfaces with an IR gun is, I believe, difficult. Has to do with the emission coefficients of different materials; Better / more expensive IR guns have an adjustment for that.
- Also, IR guns measure the temperature of a certain area, the size of which depends on the distance between the gun and the object being measured. The laser dot used to target the gun is somewhat misleading in this respect.
Anyone care to comment, esp. on #2 & #3?
IR guns can be very confusing, for the exact reasons stated above. There are a hundred different places to measure coolant temp's and no two will be the same.
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Verdad Gallardo
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
More to the point:
If the gauge in your cluster reads at all, it is probably fine. If you have a 'calibration' problem, the issue is the sending unit. The sender provides the voltage signal which is merely "read" by the gauge in the cluster.
The sending unit is most likely your problem. To check the gauge function, remove the wire/connector from the sending unit. Now, turn the car's ignition switch to "RUN" position (engine OFF). With the wire removed from the sender, the gauge should read "0" [all the way to the left on the dial]. Now, touch (and hold) the sender wire to the engine block {ground}; the gauge should read all the way to the right on the dial.
If the gauge functions as expected, replace your sender unit.
If the gauge in your cluster reads at all, it is probably fine. If you have a 'calibration' problem, the issue is the sending unit. The sender provides the voltage signal which is merely "read" by the gauge in the cluster.
The sending unit is most likely your problem. To check the gauge function, remove the wire/connector from the sending unit. Now, turn the car's ignition switch to "RUN" position (engine OFF). With the wire removed from the sender, the gauge should read "0" [all the way to the left on the dial]. Now, touch (and hold) the sender wire to the engine block {ground}; the gauge should read all the way to the right on the dial.
If the gauge functions as expected, replace your sender unit.
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
While I have gone down that path myself, three things keep me worried with this approach:
Anyone care to comment, esp. on #2 & #3?
- The water outlet is NOT where the temp sensor sits; That's in the driver side cylinder head (at least on a '70 LS5). Readings will not be directly comparable...
- Measuring metallic surfaces with an IR gun is, I believe, difficult. Has to do with the emission coefficients of different materials; Better / more expensive IR guns have an adjustment for that.
- Also, IR guns measure the temperature of a certain area, the size of which depends on the distance between the gun and the object being measured. The laser dot used to target the gun is somewhat misleading in this respect.
Anyone care to comment, esp. on #2 & #3?
In the real world IR temp guns work very well. We're not looking at determining the correct temperature to the nearest one tenth degree, we're looking approximations and trends. Accuracy within a few degrees is sufficuient for this kind of work.
An IR gun is another tool to help in determining if there is a problem and where it might be.
Pete
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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Team Owner
Joined: Jan 2006
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From: Crossville TN
If removing the sender wire (with ignition in ON position) and then touching it to an electrically grounded spot registers no indication on the cluster gauge, then there are two possibilities:
1. The sender wire is damaged so that no signal can reach the gauge. Usually, this is at, or immediately behind, the connector that attaches to the sending unit...or somewhere in the engine compartment.
2. The gauge is defective. This would be unusual...unless there was significant voltage sent to that gauge by mistake.
The sender wire is the likely culprit.
1. The sender wire is damaged so that no signal can reach the gauge. Usually, this is at, or immediately behind, the connector that attaches to the sending unit...or somewhere in the engine compartment.
2. The gauge is defective. This would be unusual...unless there was significant voltage sent to that gauge by mistake.
The sender wire is the likely culprit.
Thread Starter
Instructor
Joined: Jan 2013
Posts: 155
Likes: 2
From: Naples Florida
Temp gauge
Yes I did have the ignition switch on.
I am in the process of replacing all wiring harnesses, like I said there is some bubba tracks. Not taking any chances. I am not fond of smoke.
So far, most items repaired or replaced was BS.
I am in the process of replacing all wiring harnesses, like I said there is some bubba tracks. Not taking any chances. I am not fond of smoke.
So far, most items repaired or replaced was BS.
Former Vendor
Joined: Aug 2006
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
All of this can be found on the website Mrh747. There is more info there too...
Testing a 68-76 Temperature Gauge -or- What your non working gauge can tell you!
Testing a 68-76 Temperature Gauge -or- What your non working gauge can tell you!