Diesel Engine Installation Information
The installation position of an EGT probe is important and requires planning in your diesel engine application.
Installation locations in turbo and non-turbo engines are different for EGT probes and require consideration.
Turbo engines, it is the preferable the probe in front of the turbo inlet for higher accuracy and sensitivity. There are temperature drops (up to 250+ degrees F) across the turbine as heat is extracted from the exhaust gases, but this is not always possible; the alternative is in the exhaust pipe directly after the turbo in the dump tube. The short cast iron section of exhaust manifold and the first section of thin-walled pipe are other areas.
Regarding non-turbo engines, the long exhaust runner is most accessible. The next area for consideration is the upper section of the exhaust manifold collector.
EGT Probe Installation Methods
The probe should be installed in the exhaust manifold closest to the exhaust outlet at the head (this is the closest physical location to the exhaust valve). EGT probe placement close to the exhaust valve isn't always easy. If you don't have a turbocharged engine, the exhaust manifold can be drilled and tapped while remaining on the engine. However, doing this on a turbo engine without removing the manifold is not recommended and can potentially cause failure of the turbine from drill fragments getting into the turbine.
Drilling a hole in the thin-walled exhaust tube using a clamp style EGT probe fitting is the simplest method. A robust method is a bung welded into place, thus screwing the EGT thermocouple adapter into the bung. Stainless steel adapters are preferable and much better than brass. They withstand higher temperatures, temperature cycling, better anti-corrosion and structural stresses occurring in exhaust systems.
Diesel engine applications use long primary extractors. Placement of the EGT probe on a runner close to the head depends on your particular application. It is your decision to detect the temperature of the exhaust gases at the collector or just one cylinder.
It is not uncommon in high performance, racing and R&D applications for thermocouples to be installed at every cylinder. General use applications require one EGT probe per cylinder bank installed either near the head (exhaust valve) or at the collector.
The exhaust gas temperature is lower the further from the valve, thus leading to slower and less accuracy in EGT probe readings. However, probe installation further away from the head is typically easier since there is more room from other engine components.
Typically EGT probes are installed in different methods. Clamp type installations require a hole drilled just large enough to take the probe, and a large clamp, much similar to a radiator hose clamp, secures it. This clamp need to be good quality to withstand the high exhaust temperatures, and is often stainless steel . Alternatively, and our preferred approach, is to drill and tap the manifold or headers to accept a compression fitting that holds the probe in place. This also permits the probe depth to be adjusted, and the assembly removed and hole plugged with appropriate threaded bolt when the EGT probe is no longer required. Weld on bosses may be required on thin walled tubing sections.
Excessive EGT temperatures lead to turbo failures and / or damage to the exhaust valves and pistons. If you are after more power, you may need to lower your current exhaust gas temperature to permit increased boost and fuel delivery. Typically this can be achieved by the use of properly sized turbo dump pipe to increase exhaust flow, mixture adjustments, increased boost and improvement in the induction system for higher efficiencies.
EGT Monitor Placement
Locate the EGT gauge easily visible to the driver and with an audible alarm. This will alert the driver if safe operating temperatures are exceeded.
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