In a well-maintained standard engine, with a correctly calibrated and timed fuel injection pump, the quantity of fuel injected should rarely, if ever, exceed that which can be efficiently combusted with the mass of air available. CI engines which have been 'tuned' for improved performance are likely to generate higher than normal EGT under heavy load conditions, even if the fuelling has been adjusted on a dynamometer.
But even with the best efforts of the factory or tuning specialists, excessive EGT can still occur due to a number of not uncommon factors:
Not Enough Air
The most likely cause is a restricted air supply to the cylinders. As well as the obvious possibility of a clogged air filter element, other possible causes that have been known to affect various engines include:
- Collapsing air inlet hose/duct and on Turbo charged engines
- De-laminated or partially blocked hoses at the turbo outlet
- De-laminated or partially blocked hoses at the intercooler
- Fouled/restrictive intercooler (either internally or externally)
- Air leaks, faulty waste gate or a partially blocked exhaust on turbo-charged engines, leading to low boost pressure. (Yes, lower than normal boost pressure can cause high EGT)
Too Much Fuel
Excessive fuel delivery will also cause high EGT. This could be a result of a failure within the injection pump itself, but is more likely to be a result of over-zealous 'tuning' of the pump.
These days, many specialists offer tuning services
to turbo-diesel owners to improve towing and overtaking performance. These modifications usually provide very satisfactory results but invariably lead to the engine operating closer to the limits at full load.
If 'overdone' or if any of the other factors mentioned previously come into play, excessive EGT can quickly result - and the damage may be done before any indication of a problem is provided (if at all) by the vehicle's standard coolant temperature gauge.