Correct Thermocouple

Bending it round to just press against the surface won't give you a reliable result (I've tried similar things). Maybe a little blob of heatsink compound would help.

Heatsink compound is probably best. If you want something that will dry and provide a little strength you might check Omega's web site. Somewhere around 20+ years ago I got some sort of ceramic thermocouple paste from them. I don't recall how good it actually was, but it did dry and therefore not provide a sticky surface for dust, dirt, etc.

But it should run low not high in this situation. (reading a heated surface) Correct? I am getting readings quite a bit higher than the readout on the unit controlling the heater. If built correctly, they should be reading the temperature of the same surface, on opposites sides of the cylinders walls, which is only 0.187" thick. I am looking for confirmation that the bead type thermocouple would not read way off in a positive sense. (higher than actual)

Wouldn't expect it to read high - unless there's any other source of heat in the system (is there?).

You should not have a large thermal gradient across a metallic wall, so you can make your measurements on the outside. Select the smallest diameter thermocouple that you can easily handle. This will provide fastest response time. If you are reading higher than the wall temperature, you may have the wrong thermocouple element for the readout instrument. Make sure your thermocouple is the proper type for your read out instrument. Common types are J,K,E,and T. Also make sure you use a compatible thermocouple connection to your instrument and the that the polarity is correct. Then do a quick calibration of the thermocouple using boiling and ice water. Once those things are correct, you can clamp your thermocouple tip to the outside of the cylinder with a radiator hose clamp. You should then obtain an accurate reading.

Your thermocouple probably has a sensing bead on its end. The temperature your instrument reads is the temperature of bead, not the temperature of the surface you are attempting to measure . To obtain an accurate temperature reading you can drill a hole (called a thermowell) about 10 times as deep as the diameter of your thermocouple. When the thermocouple is inserted to the bottom of the thermowell, it will read the temperature of the housing. If you can't drill this hole, consider using a temperature indicating paint or crayon that melts at a specified temperature. These indicators are made for applications where you can see the surface and are available from Omega or a welding shop.