Efficient Engine Montoring


Temperatures will vary whenever the throttle is moved or the terrain changes. The peak number is the most important while towing, the ISB can be safely run up to 1450 for short bursts and 1350 all day long. This number is strongly affected by modifications weather it be Air flow or Fuel delivery. If air flow and fuel flow are increased equally, we can increase power to very impressive levels with no increase in EGT or smoke.

Average temps for a stock truck

Idle – 250 to 450
Cruise no load – 400 to 700
Cruise with trailer – 500 to 800
Pulling hill no load – 500 to 1000
Pulling hill with trailer – 900 to 1250

Go too high and risk
exhaust gaskets

exhaust manifold
cylinder head casting
cylinder bores

Cylinder #1 has an obstruction of the intake port caused by a casting boss for accessory mounting bolt placement plus a forward facing valve port which causes the intake air to run a maze to reach the cylinder. These reduce the airflow to the #1 cylinder, causing it to run richer than the other cylinders. Often, the exhaust manifold gasket has been cooked on cyl #1, while the others are fine.


Boost pressure tells you how well your turbo is working, weather or not you have a boost leak, and how your waste gate is adjusted.

Average pressures for a stock truck

Idle – 0
Cruising 70 mph no trailer – 5 to 10 psi
Cruising 70 mph with trailer – 7 to 15 psi
Pulling a hill no trailer – 10 to 20 psi
Pulling a hill with trailer – 15 to 21 psi

Go too high and risk these…

Intercooler Boots
Head Gasket

Again this number will vary like EGT, with throttle position and load. Air flow and fuel flow increases will make this gauge move much faster.

Fuel Pressure:

Pressure created by the electric fuel pump that carries the fuel from the tank to the filter then on to the injection pump. This has become a very important gauge on the ISB with all the fuel pump failures that have occurred and cause drivability issues. This gauge is not very exciting but when there is a problem it becomes very important in diagnosis, plus it can save a very expensive injection pump from failure due to lack of lubrication and cooling.

Average Pressures on a stock truck

Idle – 10 to 14 psi

Cruising – 8 to 12 psi
Pulling a hill with trailer – 8 to 9 psi

Absolute minimum pressure is 8 psi; anything below that and you need either a new lift pump on a stock truck or an upgraded fuel system on a modified truck

Automatic Transmission Temperature:

Temperature of the transmission fluid that leaves the torque converter and goes on to the coolers. Again not very exciting be very important to the life of your transmission and or torque converter.

Average temperatures on a stock truck

Idle in neutral or park – 140 to 160
Idle in gear – 160 to 260 depending on how long.
Cruising – 70 mph no trailer 150-170
Cruising – 70 mph with trailer 160-180
Pulling hill no trailer – 180-220
Pulling hill with trailer – 190-280 depending on load and how long a hill, or weather you can pull the hill in lock up or not

Temps will always be higher when out of lock up, because 90% of the heat generated in an automatic transmission is from the shearing of the fluid in the converter. Temps will be lower when in lock up because the input shaft of your transmission is locked to the crankshaft on the engine.

[thanks to Ted Jannetty and others, used with permission]
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