Temp gauge accuracy

-
MOPARJ

MOPARJ

What can I upgrade now?
Joined
Nov 3, 2006
Messages
861
Reaction score
7
Location
Thousand Oaks, Ca
Trying to determine the accuracy of my 72 Scamp stock temperature gauge. The rest of the gauges are pretty accurate. If the gauge has read at its warmest at about dead center with no boiling over, does anyone have an idea what the middle of the gauge translates to? 210-215 degrees?
 
A '72 scamp came with a factory thermostat of 195 degrees F.

Assuming you kept the stock thermostat middle of the gauge should be about 195. I had a '72 Plymouth Satellite and when I had a 160 degree thermostat the gauge stayed close to the cool end of the scale. When I put the correct thermostat in it read in the middle of the scale.

A note about temperatures. Cooler is not better. Engine wear is much greater at 160 than at 195. This is why new cars run at 210 or slightly higher. New cars with higher temps and low expansion pistons now routinely run over 200K miles. This does not mean you should run your Scamp at 210 it wasn't designed to run this hot.

While cooler is not better it is, or can be faster. This is why many hot-rodders run 160 degree thermostats. The lower temp allows for a slightly denser air charge and thus a few free HP, at the expense of longevity.

Regards,

Joe Dokes
 
Middle of the scale is supposed to be 200 to 210. Being a range indicator, center of its scale is center of range, considered perfect.
 
mine reads 250* on the gauge @ 190* engine temp with a 175* thermostat. Stock gauges are about as accurate as waving your hand over it and guessing
 
805moparkid said:
mine reads 250* on the gauge @ 190* engine temp with a 175* thermostat. Stock gauges are about as accurate as waving your hand over it and guessing
Click to expand...

That's funny, I've had great luck with my stock temperature gauges. The stock fuel gauges not so much :violent1:. The stock temp gauge in my Duster gives a better representation of the actual temperature than the autometer I added to have a readout in degrees. My autometer gets progressively further off as the temp goes up. By the time the actual temperature hits 200*F the autometer reads 210-212. Meanwhile, the stock temp gauge is pointing just above center of range, which tells me I'm where I need to be, as it should.

The autometer gauge doesn't even follow its own sending unit, the Dakota digital controller than runs my fans is hooked to the same sender, it gives me a nice digital readout with the push of a button that tells me my autometer temp gauge reads high. All confirmed with an infrared thermometer. Kind of annoying, since what the autometer tells me doesn't match what my fans are doing.
 
Get yourself an infrared temp pistol about 50 bucks. Point it at the boss on the intake manifold where the temp sender is to get the real temp, then look at your temp gauge to see where it's at.
 
iw378 said:
Get yourself an infrared temp pistol about 50 bucks. Point it at the boss on the intake manifold where the temp sender is to get the real temp, then look at your temp gauge to see where it's at.
Click to expand...

I agree. There were on sale for $24 at Harbor Freight last week.

Many of the parts store replacement sending units have the wrong ohm resistance.
 
iw378 said:
Get yourself an infrared temp pistol about 50 bucks. Point it at the boss on the intake manifold where the temp sender is to get the real temp, then look at your temp gauge to see where it's at.
Click to expand...

And never question the accuracy of that toy ?
Infrared light is estimating the heat coming off the surface. The fan can effect what it sees. Ambient lighting, daylight, florescent light, etc.. will too. Anyway, The water temperature below can be significantly hotter.
Look at it this way, infrared can see a man running around in the dark but if you want to know if he has a fever, you'll need to stick a thermometer in him.
 
Redfish is correct,those infrared guns are terribly inaccurate.
...temporarily install a quality gauge and then you'll know what
temperature you're operating at.
 
ir3333 said:
Redfish is correct,those infrared guns are terribly inaccurate.
...temporarily install a quality gauge and then you'll know what
temperature you're operating at.
Click to expand...

Thank you. Excuse this brief hijack. In servicing these gauges the first and deepest thorn in my side was "bend the little thingy". I dealt with that as best I could. Then this infrared crap came along. I took my website down. I give up !
Happy moparing to all
 
They are more accurate if the target color is dull black. A thermal couple provides better measurement, there are adapter modules for multi-meters.
 
Cheap way. BUT a refrigeration style thermometer, you can get a decent digi one for 20 bucks

http://viot.us/images/WT5.jpg

There are all kinds of these. Hundreds. Maybe thousands

CHECK IT FOR ACCURACY

Easy Boil a can of water on the kitchen range. Unless you live in Denver this should read very close to 212 degrees that's F as in Farenheit.

TAPE it to the bottom THE BOTTOM of your TOP radiator hose.

Improvise some insulation. This can be a towel. TAPE the towel/ insulation on there.

Be absolutely sure the fan or belts is not going to eat any of it

Run the car until stable and take some comparison readings.
 
Mine is really inaccurate. 2 tenths of a degree.That should be close enough for what we want to know.
 
I use a "candy" thermoter..there are differnet styles and pretty cheap, you can get them at Target, Walmart, etc.... I just remove the radiator cap and test the antifreeze. I always get an accurate reading. As always be careful removing the rad. cap when hot.
 

Attachments

  • 20140831_131210.jpg
    78 KB · Views: 254
RedFish said:
You still don't get it. Pour some boiling water in a coffee cup and measure the temp of the outside of the cup. This test equals what you have been doing under your hood.
Click to expand...

Sort of. The cup will reach the same temperature as the water over time. How much time depends on the thermal conductivity constant for the material of the cup. A styrofoam cup will take forever, an aluminum cup will take a minute or two. If you're checking the temperature of the water by pointing the infrared thermometer at an aluminum intake manifold next to your temp sending unit, it doesn't take much time at all for the aluminum to be the same temp as the water. Yes, the temperature curve on the aluminum will be slightly delayed compared to the temp curve on the water, but it's not an irrelevant way to check the gauge, it just won't be a perfect match. Cast iron would be slower to react, the rubber hoses slower still. Just depends on what you point the infrared thermometer at. And if it's a infrared thermometer from harbor freight, that's another source is error right there.
 
Errors in IR are related to the emissivity of the objects surface. Dull black sitck-on targets are used to help minimize significant errors. Shiny aluminum or chrome temperatures will be way off. It is best to verify the target object with a thermometer, or thermal couple. Often a IR gun is used for convenience, but without verification, it can be a misleading tool.
 
72bluNblu said:
Sort of. The cup will reach the same temperature as the water over time. How much time depends on the thermal conductivity constant for the material of the cup. A styrofoam cup will take forever, an aluminum cup will take a minute or two. If you're checking the temperature of the water by pointing the infrared thermometer at an aluminum intake manifold next to your temp sending unit, it doesn't take much time at all for the aluminum to be the same temp as the water. Yes, the temperature curve on the aluminum will be slightly delayed compared to the temp curve on the water, but it's not an irrelevant way to check the gauge, it just won't be a perfect match. Cast iron would be slower to react, the rubber hoses slower still. Just depends on what you point the infrared thermometer at. And if it's a infrared thermometer from harbor freight, that's another source is error right there.
Click to expand...

No sir. A intake will never reach the actual water temp so long as the water is flowing.
Turn the engine off and watch the temp rise at the intake and temp sender. At that point the metals become more like a heat sink in that they absorb heat from the water. If the water circulation didn't transfer heat there would be no need for the circulation.
 
RedFish said:
You still don't get it. Pour some boiling water in a coffee cup and measure the temp of the outside of the cup. This test equals what you have been doing under your hood.
Click to expand...
I GET IT DUDE ,your theory that is. First of all I do not buy diagnostic tools from harbor freight
the only things I get there is crap made from china that I can beat the hell out of like punches and such that I know I will destroy. One use items . A quality(not made in China crap) infrared gun is a great tool to have in the chest after it has been verified to be accurate. My temp pistol cost me about 70 bucks and the greatest error I have gotten from it has been 2 degrees and that's close enough for me.
 
RedFish said:
No sir. A intake will never reach the actual water temp so long as the water is flowing.
Turn the engine off and watch the temp rise at the intake and temp sender. At that point the metals become more like a heat sink in that they absorb heat from the water. If the water circulation didn't transfer heat there would be no need for the circulation.
Click to expand...

This is probably minutia, but there will always be a temperature change at the interface between materials, so even stagnant water won't necessarily read exactly what the heat source is. Flowing water provides a different Tcold (in this case, the radiator, which, with forced air is really convective cooling and not radiative) and a better heat transfer coefficient since you are going convective and not conductive.

Knowing the interfaces and heat transfer coefficients you can figure out what the source temperature is measuring the manifold, but that sounds similar to some problems I used to do in college and don't have to do anymore :)

A thermocouple would probably be the most accurate way to check the temperature gage, but rigging it into the system might take some figuring.
 
This is the setup I use to see what the gauge is reading at certain temps. I take the sensor out and put it in a pan of water. Run jumper wires to reconnect the sensor to the vehicle (don't forget the ground wire). Start heating the water and compare readings.
 

Attachments

  • Temp sender tester 002 small.jpg
    29.8 KB · Views: 173
All that comes to mind this morning is an old expression, "Out of the frying pan and into the fire". There is no theory there. The fire is in fact the hotter.
Where you bought the infrared gun and/or what you paid for it isn't the issue here. A infrared gun is in fact the wrong tool for this task.
 
You must log in or register to reply here.
-

Back
Top