March 12th, 2008 · No Comments

Exhaust gas temperature or the short : EGT.

In tuning turbocharged engines this is and should be a major concern regarding longevity of your engine and turbo.

By altering injection times, the start of injection, the injected amount and the turbo pressure you will in effect alter the temperature of the exhaust gasses that flow through the turbocharger.

As with all things metal and mechanical heat and friction are potential killers, so we must try to keep the exhaust gas temperature within the safe limits for the turbocharger.

A very good way to measure this is by using an EGT gauge or EGT meter. This probe can be installed in the exhaust manifold or right behind the turbo in the downpipe elbow.

When installed before the turbo we measure turbo inlet temperature ( TIT ) , when installed behind the turbo we measure turbo outlet temperature ( TOT ).Measuring TIT or TOT is a matter of preference, some people don’t want probes right before their turbo as it might break off and get ground up by the turbo who then self-destructs in the process. The most accurate measurement however is in the exhaust manifold. So, usually when talking about EGT people talk about TIT, for TOT add about 100-150 °C as the gasses leave the turbine cooler than they go in.

TIT installation in manifold

TOT installation in turbo elbow.

What are the common causes of high EGT’s in a diesel engine?

-A mixture that is too rich (not enough air or too much fuel). This could be caused by a restricted flow in the exhaust or intake path, outside air temperatures being high or high altitudes

-Pump timing too advanced (injecting earlier causes the temps to rise).

-Low gear driving with large load on the engine (hauling trailers and caravans). Shifting down a gear can help there.

 What are the common causes of high EGT’s in a petrol engine?

-Mixture too lean. Yes, the opposite of a diesel engine.

-Retarded timing causes higher EGT.

What is the maximum advisable EGT in a turbo diesel engine?

The general opinion for turbo diesel engines is 850 °C TIT or about 680 °C TOT as the maximum advised temperature for sustained periods. Going above them is seen as damaging.

What kind of damage will high EGT cause?

-Molten or cracked aluminium pistons.

-Turbo-vanes melting away and warping, causing unballance in the turbo which in turn causes shaft wear. Your turbo starts to go, causing even higher EGT’s. Hot molten metal bits flying into your engine is not something you want.

Tags: Technical