What is an exhaust gas temperature gauge?

An EGT gauge measures (ahem) exhaust gas temperature. This reading is directly related to the internal combustion temperature of the engine, and indirectly related to the quality of the air/fuel mixture entering the engine.

The principle is obvious: if the engine gets too hot inside, parts melt. While other gauges can give an indirect indication, only an EGT can give a direct indication that the engine is operating correctly.

EGT gauges consist of a high-temperature thermocouple (usually K-type) attached to a analog or digital readout. A hole is drilled into the chosen measurement location - exhaust manifold, oxygen sensor housing, or downpipe. The thermocouple is placed inside the using air-tight compression fittings. Simple bandclamps can also be used, but only on downpipe installations - they are not air-tight and will allow exhaust to escape.