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8/22/2019 3:27 PM  #1


Temp gague reading

Hello all, 67 mustang 390 gt.
Was wondering what temp would the motor be at if the gauge was reading in the middle. On a hot day like today mine is reading way low, I put a infer red thermometer on different parts of the motor, hottest spots only read  about 150 deg. Give or take a few. Edelbrock Aluminum heads and intake, 4 core 23 in radiator, 7 blade 18.25 fan and shroud . What temp would the gauge be reading at dead center?

 

8/22/2019 4:55 PM  #2


Re: Temp gague reading

What temperature of thermostat do you have?  That has something to do with what your gauge reads.  Gauges read differently from car to car, so we can't tell you what yours says although, a reading in the middle of the gauge usually means the water is the temp of your thermostat.  

You might take your reading from the water in the radiator.  Remove the cap when the car is up to temp and just after turning off the car to insure internal pressure doesn't come up to burn you.


Original owner - 351w,T-5, 4whl disks, power R&P
 

8/22/2019 5:14 PM  #3


Re: Temp gague reading

lowercasesteve wrote:

You might take your reading from the water in the radiator.  Remove the cap when the car is up to temp and just after turning off the car to insure internal pressure doesn't come up to burn you.

Hey, I would be very careful doing this... Even with engine shut off, you can wind up with a face full of scalding hot water...
 


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
 

8/22/2019 5:17 PM  #4


Re: Temp gague reading

I recently had a 160deg thermostat in my car and the temp gauge only read maybe a 1/4 (if that). After seeing some discussion on here about thermostats, I took Mustang Steve's advice and fitted a 191deg thermostat. Currently, my temp gauge is reading a solid 1/2 and this was at night. I am wondering if I may have gone too hot.


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
 

8/22/2019 6:20 PM  #5


Re: Temp gague reading

180 thermostat. So taking the coolant temp will give you the engine temp, and the infra red should be very close, guess ill take the upper and lower hose temps also.
K, thanx-will do tomorrow.

     Thread Starter
 

8/22/2019 6:28 PM  #6


Re: Temp gague reading

Those numberless gages are a guess. Lower 1/3 is too cold. Middle 1/3 somewhere is just right, top 1/3 is too hot.  I believe Ford intended the half way mark for decades to be “just right,” whatever that is.  On my ‘92 5.0 that stock gage read dead middle for over 20 years.  No matter how cold or hot it was outside dead middle was where it always sat. The bottom mark is 130 and the top mark is 270 so I figured the middle mark was 200. That gage has become nearly useless. I measure its uselessness by a new AutoMeter pillar mounted gage I installed which seems to function rationally. The old stock gage with a new sender registers 10-30 degrees hotter than the AutoMeter at any given time. My engine is at 27 years old and 292K miles and with cooling system upgrades AutoMeter says I never reach 210 even in 105+ heat, A/C full blast, idling at In-n-Out. Stock gage wants me to believe its 240.


'66 Fastback since July 27, 1981. Springtime Yellow, originally a 200 cu in, 4 speed. Also a '92 LX Coupe, 5.0, 5 speed.
 

8/22/2019 7:59 PM  #7


Re: Temp gague reading

I would think that the middle of the gage would be the temp of the recommended thermostat for the original engine that came in the car????

Just an opinion here but I would not remove the radiator cap while the engine is running until you have cooled it down with the water hose enough that you can place your bare hand on the radiator. Then you can remove the cap with the water running on it. You will know that the thermostat is open when you see the water flowing through the radiator. You still need to be carful because it can still flair up and burn you. The best way is to start with the engine cold and then watch the thermostat open and close.


70, ragtop 351W/416 stroker Edel Performer heads w pro flow 4, Comp roller 35-421-8. T5
 

8/23/2019 11:01 AM  #8


Re: Temp gague reading

rtmjr13@optonline.net wrote:

Hello all, 67 mustang 390 gt.
Was wondering what temp would the motor be at if the gauge was reading in the middle. On a hot day like today mine is reading way low, I put a infer red thermometer on different parts of the motor, hottest spots only read about 150 deg. Give or take a few. Edelbrock Aluminum heads and intake, 4 core 23 in radiator, 7 blade 18.25 fan and shroud . What temp would the gauge be reading at dead center?

Hi , times ago i post the result of reading with a digital sender and what the old gauge means on  the rise . 
I think was " true temp reading " 
check it 

 

8/23/2019 12:11 PM  #9


Re: Temp gague reading

There is a chart posted in the link below that references a temperature value with the needle reading. I run a 195 thermostat with an 1/8” hole drilled to the side of the spring for air to escape and my factory gauge was sent to RocketMan Classic Cougars for calibration.

The needle centered at 200 degrees and high line at 230 degrees matched my car pretty well. I verified the center mark with a infrared gun readings on the both side of the thermostat and a temperature probe into the radiator water using an adapter cap that came with my Mighty Vac hand pump. The 230 was by infrared gun alone.

 https://fyi.boardhost.com/viewtopic.php?id=9714 

One of these days, I will get a numbered gauge installed.  

At this point in life, I agree with th others about not removing radiator cap on a hot engine. 25 years ago was a different story. I would use an old shop towel to cover the cap then back off to the point it should pop free, make sure I’m at arms distance, then let it all go, and move quickly. Before I started using a heavy enough towel, the cap and water would go 3 feet in the air!! Luckily, the angels were watching over me and I never got burned.

Last edited by Bolted to Floor (8/23/2019 12:12 PM)


John  -- 67 Mustang Coupe 390 5 speed
 

8/24/2019 8:01 AM  #10


Re: Temp gague reading

When you use an infrared temp gun, I would suggest the following. 
Place a piece if black electric tape on the surface you’re checking.
Otherwise your temperature readings will be inaccurate. I’m sure you have a bare aluminum intake (or a shiny surface...since you mentioned the heads).
I learned about this at an infrared training a few years ago.
Infrared cannot shoot through glass either.
You will get a reflection temp reading...have someone in car and roll window up and down and watch them disappear and reappear respectively.
Non-stick pans, aluminum foil, ceramic coatings will be inaccurate as well.
Something like exhaust may have to use a header wrap temporarily in a spot to get a more accurate temperature.

Might be possible that your engine is as hot as temperature gauge shows.
Hope this helps.

 

8/24/2019 6:42 PM  #11


Re: Temp gague reading

Thanks for the tip Dan, I will have to look into that.


John  -- 67 Mustang Coupe 390 5 speed
 

Board footera


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