Engine How to test an aftermarket mechanical water temp gauge

MrPerfect2

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Jul 23, 2019
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I read an article - Best to test accuracy before install , but I did not ... so , my question is how to test without removing probe - to get an idea if accurate . Probe is behind the water inlet neck on manifold ( where stock sender was ) if I take reading of IR gun on the metal sender or say the hose or neck , should they be close to reading on gauge ? Point of this is to determine why my car reads hot ( mainly when A/C used in city crawl ) article said Stewart Warner gauges can be off - “ We used the boiling water test to check the Stewart Warner gauge in question, and with the probe in boiling water the gauge displayed approximately 235 degrees F! During a phone call to Stewart Warner in hopes of getting a replacement gauge, the author was told “Not to worry; that model of gauge is only accurate to plus-or-minus 14%.” Well that’s a handy explanation, since at actual 200degrees coolant temperature a 14% error would cause the reading to be 28degrees in error! We might as well not even have a coolant temperature gauge if it cannot be more accurate than those measurements.“
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You are stressing over temp readings. Let me put you at ease, coolant temp in the 220-230 range in traffic with the ac on is normal. The gauge they are testing is about the least expensive model they produce, yours is a higher end model and likely more accurate, that said if you want to test it with a temp gun point the dot into the coolant at the radiator opening where the cap is, it still may read a few degrees less than the gauge.
The metal around (actually aluminum) is going to give a higher temp reading than the coolant inside.
Hope this helps at least a little.
 
Why not put any other thermometer you trust in hot water (a thermos, or pot), and put the sending unit in the same water? You could do this right at your car. Just be careful not to burn yourself.

BTW, I think you're obsessed with this issue.
 
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“ We used the boiling water test to check the Stewart Warner gauge in question, and with the probe in boiling water the gauge displayed approximately 235 degrees F! During a phone call to Stewart Warner in hopes of getting a replacement gauge, the author was told “Not to worry; that model of gauge is only accurate to plus-or-minus 14%.” Well that’s a handy explanation, since at actual 200degrees coolant temperature a 14% error would cause the reading to be 28degrees in error! We might as well not even have a coolant temperature gauge if it cannot be more accurate than those measurements.“
To steal anothers concept... What are you going to use this data for?

This is a very common issue in the Engineering/test world. An engineer gets their hands on a slice of data, and doesn't understand why the data is the way it is... never mind that the data has ZERO impact on anything.

Are you going to shut down the car on the highway the next time you see the gauge reading hit 235F?
Are you going to pull the heads when it hits 245F?

This is very common for engineers to do, and some of the smartest engineers I've had the pleasure to work with have fallen victim to this line of thinking... I've done it myself...

In a control system, I would want better than 14%, but this is for a display gauge...


Why do you think your radiator has an issue?
 
Hitting 240-245 degrees in 95 degree ambient temp . Reason for radiator is deduction - has new 192 thermostat , water pump is older ( but flows good ) new heavy duty Hayden fan clutch , fan shroud , air dam under car , burped air - overflow tank - did some IR readings on outside of radiator when car was idling at 235 - various readings from 200 to 150 ( leading me to believe cool spots in tubing - clogs ? ) water going in the radiator was 235 ( IR reading on upper hose ) water going out radiator was 200 ( IR reading on lower hose ) I am guessing 35 degrees is not enough cooling - btw the temp gauge and upper hose are on sync ( so gauge is good ) can’t send video , but screenshot of flow in radiator below - my guess is some parts of radiator tubes are restricted and not getting good heat transfer
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I may be wrong but I believe we've all hashed out this coolant temperature with you in one of your first threads. I just left the oil dip stick obsessive thread that devolved into an eHarmony listing. That thread has several folks gently telling you that you worry too much about things we've made it past twenty years ago. I believe it was your thread that forced me to consider a UFC maneuver to convince you against putting under drive pulleys on your car. :D
So save yourself undue stress and enjoy fixing the things that do and will matter as you own that old car! Trust me. There will be plenty.

To summarize:
Do any of these matter?
-4 HP from underdrive pulleys. NO
-4.5 or 5.5 qts (1 qt spread) of oil mattering until you mark the stick next time. NO
-10 degrees of water temp up or down NO

On a good note....you have made it past the PITA new member place where some are never heard from again so congrats! I hope this small attempt at constructive humor sits ok with you. ;)
 
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