Diagnosing with a temperature gun.

Diagnosing with a temperature gun.

August 7, 2018 0 By Ray Bohacz

The ability to quickly determine the temperature of a part without any disassembly is a wonderful aid when things go wrong. All it requires is an infrared temperature gun and applying logic of how the component functions. In some cases heat will be an indication of a problem while in others it will be a lack of temperature. Think it through in your mind. Some common tests and the expected results are provided here.

Engine misfire: To determine which cylinder is misfiring on either a gas or diesel engine, measure the temperature as close to the exhaust port of the cylinder head as possible. Compare this reading with the other cylinders.

If the cylinder is not burning the fuel (bad ignition wire, fouled spark plug or failed/lazy injector/nozzle) it will be cooler than the others. Think simple first; do look to make a small problem into something big. Lean bores will be hotter on a gas engine under load.

Confirmation of engine coolant gauge: Measure the temperature at the location of the sending unit for the gauge (usually it is a single wire sensor). It should read within reason of the gauge. If not the sending unit/gauge/wiring is the problem.

Engine oil temperature: To confirm engine oil temperature shoot the oil pan and if possible the oil filter. There will be a small amount of heat loss but it will be close enough for diagnostics.

Blockage in radiator/intercooler/oil cooler/heater core: Follow the liquid or air flow into the heat exchanger. It should drop in temperature as it travels through it. Look for either excessively high or low temperature spots to find a blockage.

Excessive brake drag: Measure the drum or rotor temperature to find a dragging brake shoe or pad.

Stuck thermostat (open or closed): When stuck closed the temperature will be high on the engine side of the thermostat and low on the outlet. If stuck open it will be almost the same on both sides of the flow in and out.

Tires: When balancing tire pressure on a machine that is in the sun keep in mind that for every 10 degrees F change the pressure is skewed by one psi. For example, the ambient temperature is 60 degrees F and you want 32 psi in all tires. The temperature of the tires in the sun is 90 degrees F. Those will need to read 35 psi on the gauge to be 32 psi when they drop to 60 degrees F.  It is not perfect but very close.

Bearings: A bearing will run hotter when it is starting to fail. Find a noisy bearing on any machine by taking its temperature.

Planting seed: Dig to the intended seed depth and measure soil temperature.

The possibilities are endless if you just apply some American farmer ingenuity!