What Causes High EGT In A Diesel?

Diesel engines are not impervious to damage. Few things will harm or kill a diesel engine faster than high exhaust gas temperature (EGT), but oddly enough, no diesel pickups or RVs come standard with a pyrometer to monitor EGT. EGTs in such cars normally stay below safe limits during regular operation, but scenarios can arise where the EGT becomes too high, causing catastrophic engine damage without warning to the driver. A pyrometer that shows the EGT of a diesel engine can alert the driver to unsafe situations before they cause harm. That’s presumably why the Banks DynaFact pyrometer is one of our most popular things, and why many of our power systems contain a DynaFact pyrometer.

A pyrometer is a temperature gauge that can measure temperatures that are higher than those that can be measured using a regular thermometer. It comprises of a temperature-sensing probe (thermocouple) that is placed in the measurement region, or flow. The probe is attached to a gauge that is set back from the high-temperature source. The pyrometer sensing probe is located in the exhaust manifold or directly after the turbocharger’s turbine exit, and the gauge is mounted in the driver’s compartment on a diesel. The goal is to measure and display EGT in Fahrenheit degrees (F.). The EGT is also known as the turbine inlet temperature when the probe is placed before the turbine section of the turbocharger. Turbine output temperature is EGT measured after the turbo, as you might anticipate.

Some mechanics are hesitant to install the pyrometer thermocouple in the exhaust manifold because they are concerned that the probe will break or burn off and blast into the turbocharger. Such a piece of foreign material entering the turbine would do considerable damage, potentially breaking the turbo’s compressor wheel and sending broken parts into the engine’s intake system, causing even more harm. While the foregoing situation is frightening, it is also improbable. To avoid this, today’s high-quality pyrometers have thermocouples that are sheathed in stainless steel. A diesel mechanic who can honestly say he’s never seen a thermocouple fail and fall into the turbo on a diesel pickup or motorhome is extremely rare. With a decent pyrometer, this simply does not happen.

It’s mainly a matter of finding a good installation place or convenience whether the pyrometer thermocouple is mounted before or after the turbine. It should be noted that the turbine outlet temperature at full speed or under a heavy load is normally 200o to 300o F lower than the EGT reported in the exhaust manifold when the EGT is taken after the turbine. The amount of heat energy in the overall exhaust gas flow that was used to drive the turbocharger is shown by the temperature drop after the turbo. The total flow and speed of the flow through the turbo are also related to the temperature drop through the turbine. The turbine outlet EGT may be as much as 500o F lower than the turbine inlet temperature at part throttle, under mild load, such as cruise settings, yet the overall exhaust flow is substantially lower than at full speed. The exhaust gases just don’t have enough time to give up as much heat energy as they rush past the turbine at high turbine speeds (under heavy load). Because of this variation, thermocouple installation in the exhaust manifold is thought to be more precise. All of the EGTs addressed in the following sections are turbine inlet temperatures.

Any turbo-diesel vehicle should have a decent pyrometer installed, according to Banks. It’s a cheap modification that keeps the driver’s engine out of problems with EGTs, and it can even serve as a guide to optimum fuel economy, but more on that later. See Banks DynaFact Gauges for further information on the Banks pyrometer.

So, what is the significance of EGT? EGT measures how hot the combustion process is in the cylinders, as well as how much “afterburning” is taking place in the exhaust manifold. The air/fuel ratio has a direct impact on EGT. In a diesel, the higher the air/fuel ratio, the higher the EGT. Under heavy loads or at full speed, there are two things that can cause a rich mixture: too much fuel and not enough air. That seems simple enough, but the second half, not enough air, is what might cause problems in a stock, unmodified truck or RV. Any restriction in intake airflow, or intake air density, reduces the amount of air mass that reaches the cylinders. Consider the amount of oxygen that gets to the cylinders to sustain fuel combustion. A dirty or restrictive air cleaner, a partially blocked air intake, a high outside air temperature, a high altitude, restricted airflow to or via the radiator or intercooler, and a high water temperature are all examples of this. A cooling system problem will be indicated by the vehicle’s water temperature gauge, but other issues are unlikely to be detected without the use of a pyrometer unless the driver sees excessive exhaust smoke. A pyrometer also reacts faster than a water temperature gauge, allowing the driver to notice an issue and avoid engine damage sooner. A restrictive exhaust system can also impede engine airflow, resulting in a rich state. If the vehicle is working hard, such as pulling a big load, running at a high speed for an extended period of time, or climbing a long grade, any of the following factors can cause excessive EGT.

Excessive EGT has already been highlighted as a cause of engine or turbocharger damage, but let’s get more specific. The design and materials used in the various parts of the turbo-diesel determine which parts fail first, however the turbocharger is frequently the first to fail. The square corners at the outer extremities of the vanes, where the material is weakest on the turbine wheel, can become incandescent and then melt under sustained high EGT, resulting in the square corners being rounded off. Consider yourself fortunate if you or your mechanic notices this symptom before anything more serious occurs, because shortly after the tips melt, the turbine wheel loses balance and wipes out the turbocharger bearings, which may or may not result in shaft failure and destruction of the turbine and compressor wheels. Excessive EGT can also cause the turbine housing to deteriorate or crack. Due to the increased heat energy, high EGT can drive the turbocharger into an overspeed condition that exceeds the designed operating speed. Either the turbine wheel or the compressor wheel may explode as a result of this. Excessive EGT will destroy the pistons if the turbo does not start initially. Piston deformation, melting, burning, holes, cracking, and other types of damage can occur. If you slightly burn a piston top, the engine may continue to run without problems, but the next time you run extreme EGT, more damage may be done, and so on, until the engine fails. Piston failure can be disastrous, which means highly costly. At the very least, an engine overhaul will be required, which is also costly. Excessive EGT can also lead to cylinder head and exhaust manifold fracture. High EGT might also cause exhaust valve failure. Aluminum engine parts will be among the first to be damaged, as aluminum has a lower softening and melting temperature than steel or cast iron. Aluminum pistons and cylinder heads are used in a rising number of diesel engines.

So, what does it mean to have an excessive amount of EGT? Even for extended running, mile after mile, 1250o to 1300o F. is a safe turbine inlet temperature if everything is working properly. Things can get a little tense as the temperature rises above 1300 degrees Fahrenheit. Keep in mind that EGT damage accumulates over time. When the temperature rises above 1400o F, you’re usually playing against a stacked deck, and it’s just a matter of time before you lose. The shorter the period is, the higher the EGT.

As previously stated, large EGTs occur when there is too much fuel for the available air. When EGTs exceed 1300 degrees Fahrenheit, the quickest way to minimize the amount of fuel going to the engine is to ease off on the accelerator pedal. Downshifting is another option if your speed allows it. While the engine may be capable of pulling the load in fifth gear at high EGTs, operating in fourth gear at lower EGTs is far easier on the engine, as long as the engine’s RPM red limit is not surpassed.

How do you keep your EGT down?

Intercooler and exhaust manifold to be upgraded. Upgrading the turbo will lower the EGTs by more than 200°, but without more aggressive tuning and some larger injectors, turbo lag will occur. The standard turbo will be happier if you get the old gal to flow more air.

What is the maximum EGT diesel?

It’s debatable what the absolute maximum safe EGT range is. We recommend not exceeding 1250° F and not operating in the 1200° F – 1250° F range for a lengthy period of time, regardless of engine make/model/year. This is a cautious estimate, but 1) engines and engine components are costly to replace, and 2) the range is quite manageable. Many high-performance engines will experience exhaust gas temperatures well beyond this boundary in racing and sled pulling, but it’s important to remember that these engines were designed to withstand such abuse. To understand why this advise is made, it’s necessary to grasp a few critical aspects that limit an engine’s ability to withstand high exhaust gas temperatures.

To begin with, a high exhaust gas temperature is the result of a high combustion temperature and an inefficient burn – if the exhaust gas temperature is 1200° F, the combustion temperature is much higher. Factory pistons are commonly made of an aluminum alloy with this in mind. Aluminum has a melting point of about 1,200° F in its basic state. Fortunately, the fact that combustion occurs quickly and the piston is constantly cooled prevents heat from entering the piston. However, the higher the temperature applied to the piston’s face and the longer it takes for this heat to transmit, the greater the risk of the material yielding.

Heat-resistant iron and steel alloys, such as those found in turbochargers, absorb heat at a significantly slower pace. A turbine, on the other hand, can spin at speeds of over 100,000 rpm, exerting a massive centrifugal force on the rotating turbine wheel. The chance of failure increases exponentially as exhaust gas temperatures rise. This is in addition to the fact that oil in the turbocharger bearings can begin to boil. As a result, it’s critical to think about how EGTs affect a turbocharger and the strain it puts on its components. Furthermore, today’s cylinder heads might be composed of aluminum or cast iron. Head gasket failure is a possibility when exposed to high temperatures on a regular basis. The cylinder head may begin to distort and/or the yield stress of the head bolts may be dramatically lowered when the material absorbs heat.

We tend to err on the side of caution when it comes to EGT control because of these variables, as well as the high cost of replacement or repair.

Pyrometer basics

A pyrometer is a device that measures and displays the temperature of exhaust gases. The pyrometer, or pyro, itself, a thermocouple, and a calibrated wiring circuit are all included in a standard pyrometer. A thermocouple is a temperature sensor that works on the voltage formed when two dissimilar metals come into contact. A tiny voltage proportionate to the temperature of two dissimilar metals in contact will result. As a result, the pyrometer gauge reads the voltage across the thermocouple (on the order of millivolts). The thermocouple is commonly referred to as the “probe” in pyrometer setups. The probe is usually inserted in an exhaust manifold or turbocharger up-pipe in the exhaust system. The current EGT is relayed to the driver almost instantly by a pyrometer. In modified diesel engines, it’s critical to keep an eye on the pyrometer at all times, and it’s also a good idea in stock applications.

Either an exhaust manifold or a turbocharger up-pipe should be used to house the pyrometer probe. Installing a pyrometer probe at the turbocharger downpipe is not recommended since the exhaust gas temperature at the turbocharger outlet is always lower than, and in some cases much lower than, the temperature at the turbocharger inlet. This is because a turbocharger is a waste energy recovery device: as the turbocharger converts the engine’s waste heat on the turbine side into pressurized air on the compressor side, energy is extracted from the incoming exhaust stream, lowering its temperature at the outlet as a result of the energy conversion across the turbine. As a result, knowing the temperature at the turbocharger’s input is essential.

Does intercooler reduce EGT?

An intercooler will simply chill the intake charge, deliver more oxygen to the cylinder, and lower EGTs in an engine that does not have one.

What’s a good EGT temp?

We can absolutely declare that any engine running at 1,800 to 2,000 degrees EGT for more than a second or two should be rebuilt every season and may incur turbocharger, cylinder head, or piston damage during the season, based on our own experience in the sled pulling and drag racing worlds. It’s simply too much to expect a diesel to operate at those temperatures. We’d think 1,200 degrees is a safe number for towing, with occasional spikes of up to 1,400 degrees acceptable while climbing hills. EGT works in a similar way as placing something in the oven. Nothing happens if you put your hand in a hot oven for a second or two. You’ll get burned if you leave it in there. In a diesel engine, the same thing happens. The longer an engine is subjected to high EGT, the more likely it is to be harmed.

How does AFR affect EGT?

It’s worth noting that the goal EGT is only valid on the same engine configuration as the dyno. The ideal EGT may alter if the ignition timing, cams, pistons, headers, and other components are changed. At the same AFR, increasing the compression ratio without making any other adjustments will lower the EGT. At the same AFR, delaying the ignition timing will often raise the EGT. One engine may produce the most power at 1350 degrees, whereas another engine may prefer 1500 degrees. You can’t just guess at this; else, you’ll be wasting your money on instrumentation.

What is normal exhaust gas temperature?

The amount of exhaust gases produced by diesel engines varies depending on the engine’s speed and load. The maximum temperatures are produced by heavy loads and high speeds. In general, temperatures in the exhaust gases of diesel-cycle engines range from 500–700°C (932–1293°F) at full load to 200–300°C (392–572°F) at no load. The temperature of exhaust gases generally discharges about 420°C (788°F).

Many occurrences have been reported in which fumes from a leak were ignited by the exhaust of a diesel engine. To avoid the dangers of exhaust gases acting as an ignite source, several strategies are used. They might be routed to a safe area, or water sprays could be installed in the exhaust piping to reduce their temperatures. Combustible building should never be exposed to exhaust gases.

Will a bigger exhaust lower EGT?

It decreases EGTs by allowing the turbo to breathe more freely, allowing more exhaust gasses to escape. It’s more fluid now. It’s critical to keep egts cool because if you don’t, you risk melting a piston and causing damage to the engine.

Does more boost lower EGT?

This turbo shell is made of high-quality A-356 aluminum alloy and is both light and sturdy. It’s equipped with a billet CNC compressor wheel that’s engineered to provide maximum boost at all levels while reducing turbo lag and compressor surge. Your diesel engine will have a smooth power curve if you supply a smooth, consistent air intake flow. Faster spool-up and a boost curve that better fits engine needs are also achieved thanks to the lighter compressor wheel and improved vane design.

The internals of this turbo were also built to last by APP. A larger turbine shaft, improved step-gap oil seals, superior bearings, and greater quality control all contribute to a more consistent product than the original stock one.


According to the specifications, the APP turbo features a 62mm inducer wheel and a 92mm exducer wheel, compared to the standard unit’s 60mm and 80mm. While the wheels are larger, the casing is only slightly larger than the stock unit, allowing it to fit into the existing space with ease. The new turbo also includes a brand-new billet aluminum adjustable wastegate actuator that is pre-set at 24 psig. The factory unit’s pressure is set to 8 psig. Other enhancements over the OEM turbo include: The turbo shaft has a greater diameter than the stock unit (22 percent at the hub and 16 percent at the journal bearings). The thrust bearing’s contact area has been expanded from 270 degrees to 360 degrees. For better sealing, a step-gap oil seal was added to the turbine side, and the turbo inlet was increased from 3 inches to 4 inches. To make installation with the larger inlet easier, APP includes a new silicone intake tube and T-bolt clamps. All intake air passes via a ported-shroud housing, which is more efficient than the stock unit. When you combine the larger turbine and compressor wheels, the more efficient housing, and the higher wastegate actuation point, you obtain superior performance.

Is EGT gauge necessary?

A good EGT gauge is essential if you’re tinkering with the fuel/air ratio, installing a larger turbo, or running higher boost. Without it, the engine may become overheated and cause damage.