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Checking engine temperatures

1418 Views 6 Replies 4 Participants Last post by  gwscheil
Has anyone else tried using an infrared thermometer to check engine temperatures? I bought one recently when the price of a basic unit dropped to $50. Mine is a Sentry model ST650 with a pistol grip, range to 999F, 12:1 focus spot, and switchable laser pointer. It basically reads the surface temperature of almost any non-polished surface. Direct contact is not necessary - spot size is about 1.5 inches at 10 inches, hitting maximum focus at 40 inches with a 3 inch spot. At a couple of inches it probably reads about a 1/2 inch spot.

The backhead and smokebox readings on my Ida are pretty close to expected. The main boiler readings are not very useful due to that empty saddle tank. With a little experience, it should be able to tell when you are overfiring or running low on water. Readings on fuel tanks, piston housings, etc. are sometimes interesting. It should not read steam unless reflectance is very high.
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George, I bought one from Harbor Freight and have noticed that it does not like shiny surfaces as you say. I tried using it on my as yet unpainted Mason Bogie and most of the temps I got were obviously low, like the smoke box too hot to touch was reading about 80 degrees. I'm hoping it wil be more accurate on painted surfaces. I haven't tried it on either of my other locos.
You can calculate the temperature of the contents of the boiler via the boiler pressure (psi). The calculator for this is online at the website "eFund" (Engineering Fundamentals). You can do pressure to temp or temp to pressure.

So far, even white painted surfaces seem to be accurate. I bought it to check the house for heat losses and it found some unexpected locations. For steamers, I hope it will be able to quickly warn of overheating problems without loss of skin or eyebrows. Way to cold now to make any more tests - 1 degree at 9:30 in the morning.
As Chris stated, saturated steam temperature is a function of pressure. Without bothering to look up the table in a thermo book, the answer is 400 degrees. (or 4 bars)
Getting the temp of steam from a table is fine if all you are interested in is the boiler temp. However I personally am also interested in the temp of things like the cylinders, smoke box, stack, back head, gas tank, etc. For those things a remote sensing thermometer is great if it is accurate.
So far, only Ida's cylinder temp may be off, but it also a small target. Backhead, smokebox, and fuel tank are all pretty reasonable. Still too cold to try Willi or Mikey yet.
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