Best Cummins EGT Probe Location

Pyrometer positioning on a Cummins Dodge Ram


What is a Pyrometer?

Pyrometers or Exhaust Gas Temperature (EGT) sensors are used in a variety of applications where there is a need to measure high temperatures. Here at XL Mechanical Service we have installed many of these over the years. As the name suggests, usually the medium measured is a product of burning, or combustion if we analyse the case of an internal combustion engine.

Why do we need Pyrometers?

During development, engine manufacturers use pyrometers installed in the exhaust manifold of their test engines to accurately monitor temperature changes. This is one of the most accurate ways of determining the quality of combustion and prevent excessive thermal and mechanical stress on internal and external components. While an engine is developed, engineers change the fuelling characteristics constantly to find the best balance of power, consumption and emissions. During overfuelling, high temperatures and pressures occur in the cylinders, so by having an EGT sensor measuring temperature changes will help prevent engine failure. Typical components which suffer failures from prolonged exposure to high temperatures are valves and valve seats, piston crown, piston rings and turbochargers.

Why can’t we just use the coolant temperature sensor?

On liquid-cooled engines, heat from the cylinder walls is transferred to the coolant. Then the coolant circulates around the block increasing its temperature even further and then it goes to the head. It still picks up more heat, until it reaches the thermostat where (in the case of an up-to-temperature engine) it is directed to the radiator. The coolant temperature is measured near the thermostat. If you carefully analyse the heat transfer path described, you will realise that if the temperature of the cylinder increases, this will cause the coolant’s temperature to increase, but because it still has to travel, the coolant temperature sensor will provide a delayed response.

What is the benefit of installing a pyrometer to my Cummins engine?

Vehicle owners might want to install an aftermarket pyrometer in their engine’s exhaust manifold so they can quickly monitor changes of exhaust temperature. This would help in preventing valve or turbocharger failure (believe me, that’s an expensive repair!), or even detect injector or pump failures, especially on mechanical engines.

Where is the best position to install an EGT sensor in my exhaust manifold?

So where is the best position to install an exhaust pyrometer on a Cummins ISB, commonly found in a Dodge Ram? It depends on how accurate you want the measurement to be! Let’s analyse this step-by-step and reach a logical conclusion.
Cummins B series 12 Valve mechanical engines in Dodge trucks (1989 onwards), ISB 24 Valve (1998 onwards), and Commonrail ISB 24 Valve (2003 onwards), have the same coolant path.

Picture 1 – Cummins ISB EPA 2017 coolant flow

As we can see in Picture 1, Coolant travels from the inlet (1) into the pump (2), then to the oil cooler cavity (3) and finally into the engine block (4) to cool down the cylinders.
Considering that the pump (2) is at the front of the engine, which cylinder is the last to receive coolant? That’s right! Its number 6. Typically, cylinder #6 will run a little bit hotter than the rest due to cooling system design and limitations. This means that if you want to install a pyrometer to your exhaust manifold, you would get quicker and more accurate results if you install it as close as possible to exhaust port #6.
Remember that early detection of overfuelling will save you money!
Desired EGT sensor locations
Here are some examples of exhaust manifolds of two generations of Cummins ISB engines. We have marked the ideal pyrometer position on engines without EGR cooler (Picture 2) and with EGR cooler (Picture 3).

Picture 2 – Pyrometer positioning on Cummins without EGR cooler

Picture 3 – Pyrometer positioning on Cummins with EGR cooler

Tom Zelinka has been an Alberta Journeyman Automotive Mechanic and Interprovincial Red Seal since 1978. In 1981 he then received his Alberta Journeyman Heavy Duty Mechanic Certificate and Interprovincial Red Seal. He has received Certificates for:  Cummins engine certification on N855/N14/M11 Engines, Cummins B/C/ ISB Series Engines, Cummins B/C/ISB Series Engine Fuel Systems, and Cummins B/C/ISB Series Electronic Engine Controls.

Interprovincial CFC/HCFC/HFC certification, Alberta Liquid Petroleum Gas Certification, Alberta Certified Advanced Mobile Hydraulics, Alberta Certified Diesel Engine Control Systems.

As the technology and models change, Tom continues to stay on top of the industry to be sure that you are receiving superior service for your Dodge Cummins diesel truck.

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