J'ai (enfin) trouvé quleques des infos sur les EGT (Exhaust Gaz Temperature).J'ai converti les °F en °C, mais n'ai pas eu le courage de traduite
Pour ceux que cela intéresse .... désolé pour la longueur !!!Arnaud
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Exhaust Gas Temperature (EGT) is a good indicator of your engine's performance. Accuracy in Exhaust Gas Temp (EGT) is very important. The
turbo doesn't make heat; it absorbs the heat and uses the exhaust pressure. As the exhaust is blown across the turbine blades, the blades spin
at incredible speeds. The shaft of the turbine wheel is slaved to the compressor wheel so they spin together. When you spool up the turbine, the
compressor turns as well. Generally speaking, the faster it spins, the more boost the turbo will make. The problem comes when you're trying to
turn the turbine too fast. To do this, it takes a lot of heat and pressure. If you get the turbine too hot, it can damage the turbo. At 1270 degrees F,
the tips of the turbine blades begin to blow. If you get them too hot, they'll straighten out or even melt and you'll ruin the turbo. The factory Garrett
turbocharger will pull all day long at 670°C, but in our opinion, 700°C degrees is the DO NOT EXCEED temp for sustained use.
There is contradictory opinion and advice about the best place to install the temperature reading device (thermocouple) that supports the
pyrometer, but there is no disagreement that watching EGTs with a graduated gauge is a good thing to do.
EGT's will run about 150°C at idle to 760°C under an extreme load (such as merging onto the interstate with 25,000 lbs.) Normal running temps
will be between 260°C to 500°C. With EGT's at 300°C, the 7.3L engine wis operating at its peak efficiency. Complete combustion is being
achieved and converted into usable horsepower and torque as efficiently as possible. Maximum fuel mileage is achieved at this point. Above
300°C the engine gets wasteful with the fuel due to load demands. Below 300°C and you lose efficiency (Power and Torque). So when you're out
on the road, pay attention to the gauge. If EGT's start to creep up, simply ease out of the throttle.
Some publications dealing with EGT temps favor Turbocharger Inlet Temp (TIT) and not Turbocharger Outlet Temp (TOT). This suggests that the
thermocouple should be mounted Pre-Turbo (in the exhaust manifold) and not Post-turbo. (in the down pipe) In their view, if you choose to mount
the thermocouple in the down pipe, EGT readings will be inaccurate. With the thermocouple in the down pipe, the gauge reacts more slowly and
is reading the TOT which is lower than the actual temp of the turbocharger. The difference between TIT and TOT can be as little as 10°C to as
much as 200°C under a heavy load.
One expert gauge manufacturer suggests that mounting the thermocouple in the downpipe and watching for a sustained temperature of 570°C, is
just as good as mounting in the pre-turbo position.
The most convenient installation of the thermocouple for a TIT application is in the lowest point of the driver's side exhaust manifold. The manifold
itself is made of a high silicon cast iron and is very easy to drill and tap. There is a place on the manifold that makes for an easy installation and
since it's the lowest point of the exhaust manifold, the metal chips are easy to clean out. (Greasing the drill bit to capture and contain any loose
metal chips does not seem to help much. Some owners drill with the motor running to blow the metal chips out in real time.)
The best location for installation of the thermocouple for a TOT application is in the downpipe as close to the turbo as possible.
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A pyrometer is a temperature gauge designed to measure high temperatures above those measurable with an ordinary thermometer. It consists of
a temperature-sensing probe (thermocouple) that is placed in the area, or flow, to be measured. The probe is connected to a gauge, which is
located a safe distance away from the high temperature source. On a diesel, this means the pyrometer sensing probe is mounted in the exhaust
manifold or immediately after the turbine outlet of the turbocharger, and the gauge is mounted in the driver’s compartment. The purpose is to
measure and display EGT. Where the probe is positioned before the turbine section of the turbocharger, the EGT may also be called the turbine
inlet temperature. As you would expect, EGT measured after the turbo is called turbine outlet temperature.
We might mention that some mechanics fear installing the pyrometer thermocouple in the exhaust manifold for fear the probe will break or burn off
and blow into the turbocharger. Such a piece of foreign material entering the turbine would cause serious damage that could in turn break the
compressor wheel of the turbo, sending broken pieces into the intake system of the engine where even more damage could occur. While the
above scenario is scary, it is also unlikely. Today’s quality pyrometers feature thermocouples that are sheathed in stainless steel to prevent just
such an occurrence. It is exceedingly rare to find a diesel mechanic that can honestly say he’s ever seen a thermocouple that has failed and
fallen into the turbo on a diesel pickup or motorhome. It just doesn’t happen with a good pyrometer.
Whether the pyrometer thermocouple is mounted before or after the turbine is usually a matter of finding a suitable mounting location, or of
convenience. It should be noted that when the EGT is measured after the turbine, the turbine outlet temperature at full throttle or under a heavy
load typically would be 90°C to 150°C. lower than the EGT measured in the exhaust manifold. The temperature drop after the turbo indicates the
amount of heat energy in the total exhaust gas flow that was used to drive the turbocharger. The temperature drop through the turbine is also
related to the total flow and speed of the flow through the turbo. At part throttle, under light load, such as cruise conditions, the turbine outlet EGT
may be as much as 260°C. lower than the turbine inlet temperature, but the total exhaust flow is much less than at full throttle. At high turbine
speeds (under heavy load) the exhaust gases simply don’t have time to give up as much heat energy as they speed through the turbine. This
variance is why installation of the thermocouple in the exhaust manifold is considered more accurate. The EGTs discussed in the remainder of
this article will all be turbine inlet temperatures.
Bravo Arnaud 
