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Discussion Starter #81
Just coming back to this:

What are these temp gauges supposed to reflect when the dial hits the top mark?

I had my '56 hit this position yesterday, hot day with freeway driving then return home to stop/start traffic, and the thermometer gun reading on the stat casing was 205˚F.

Previous thread says this top mark should actually indicate 230˚F. Is there consensus for that? (Temperature gauge calibration.)
 

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Cocke County, TN. 55 Bel Air Sport Coupe
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Most of those infra red thermometers have an accuracy of about +- 20% at best aiming them at uneven surfaces, and pretty bad even for smooth surfaces. Try hanging a piece of sheetmetal and an "old fashioned" thermometer close to each other, away from a heat source, let the temps stabilize, then measure the sheetmetal with the infra red and compare it to the thermometer to see how close they are. Start pulling the infrared one back and back and watch the readings change. Another test, spray paint sections of the metal flat black, gloss black, and silver and see the different readings for the same piece of metal different colors. Also don't think that the little laser pointer has anything to do but make it look cool. At a few inches the guns measure a spot about 2" wide. The further you go from the thing you are measuring, the wider the test circle gets. A DMM with a thermocouple and a dab of heat sink compound will give you some real world temp readings.
 

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I was having a very similar issue with my 55. Hot summer driving in Houston. I had accidentally installed a 180 degree tstat when I swapped manifolds. After going back to the 160 tstat, I never saw the guage read that high again.

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Discussion Starter #85
Geez ... will have to test the temp gun. But the way I use it the results are consistent ... multiple readings and I go to the same four places every time.

I am about 6” to 18” inches away from the target, but the same for each one: thermostat case; top hose; radiator front face; bottom hose. (Bottom hose is more like a 24” distance, though.)

Interesting with this motor, the temps do not fall as quickly once I get going again – even though it is the same radiator. (Same 160 degree stat.)
 

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There are so many causes for overheating, Jon. Personally I have found that the IR type temperature guns are pretty good, if you get a good make, having compared calibrated temperature probes to the gun reading. 205° is more than I like to see in a Gen 1 SBC, so it looks like somethings not right.
Here's some overheating faults I have found (speaking of stock setup here).
  • wrong radiator core fitted - most cores these days are suited for force fed fan systems ala modern cars
  • incorrect or stubborn thermostats, out of 10 you buy, 6 will be faulty. This caused by faulty returns being restocked.
  • bottom hose sucking flat, most bottom hoses now sold without the inside spring.
  • incorrect radiator/fan position, too close air "stalls", too far, not enough air pulled through the core.
  • slipping fan belt, most of the replacements available in AUS/NZ don't fit properly, I had a 11A type which I replaced with a 3/8" OEM type from USA, problem solved.
  • sludged up system, water can't flow.
  • retarded ignition timing
  • fuel a/f not optimal
  • binding brakes.
  • mis-aligned wheels/tires
Add to this the aftermarket coolant temperature senders not able to report correctly. Speaking of '57 type, I've got 3 junk ones out there that don't read right, mostly over reporting. If you can find an OEM unit, go with it. They seldom go bad.
 
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Just a note on IR type temp sensors. Most will not give accurate temp readings on soft surfaces. So things like hoses wont read as accurately as hard surfaces like the T stat housing, block, intake, etc.
 

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Discussion Starter #88
Thanks for the checklist, Rod.

I'll be watching it again when the new distributor is in – that's the biggest change to (hopefully) complete this.

Interestingly, once the engine was getting hot even highway driving would not bring it down as much as I wanted.

Will report back.

Also interesting about the soft surfaces thing, 1971BB427 – I'll test that too. (The readings off the rubber hoses are certainly consistent, one to another, but I'll compare with the radiator front and see what the difference is – should not be much, if anything, between that and the top hose.)
 

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Take a reading on the hose outlets right next to the hose also. It will give you an example of how the metal at near proximity to the hose differs in temperature readings. Not a huge difference, but it does usually read a decent amount.
 
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