Originally Posted by cptgregger
I don't know about the newer diesels, but on the 2nd gen Dodge Cummins (98.5-02), despite conventional wisdom assuming it's ok to idle a diesel, idling that particular motor for more than 10 minutes is bad for it.
Idling any diesel engine at low idle RPM for more than a minute or so is a no no. Warming up a cold diesel engine by idling the engine at low RPM is a no no if you want the engine to last a half-million miles or more. Combustion chamber temps fall too low to provide complete combustion, and the result is a sticky tar-like mess called wet stacking that coats the valve seats and eventually results in an engine that won't run right.
Power Stroke diesels have options that elevate the idle RPM to high enough to result in combustion chamber temps that will support complete combustion. My '99.5 Power Stroke had logic built into the main computer (PCM) that elevated the engine idle RPM any time the engine was idling with freezing cold intake air temp (IAT). Mine also had an optional black box called an auxiliary idle controller (AIC) that could be set to automatically elevate the idle from low idle of 670 RPM to high idle of 1,200 or 1,300 RPM any time the engine was idling with the tranny in park and the parking brake engaged. Newer Power Strokes replaced the AIC with a built-in Stationary elevated idle control (SEIC) logic in the main computer that must be activated before it will work.
But in Texas heat is usually our problem, not cold IAT. So I used my AIC to elevate the idle RPM so the Air Conditioner would put out more and colder air to keep Puppydog happy while I was in Wal-Mart or the Mall or the SuperMarket. At low idle RPM the AIC didn't do much good, but at 1,200 RPM it did fine in 100° ambient temps to keep my CrewCab cool. I had that pickup for over 10 years, and never had a problem with someone trying to drive off with my idling pickup with the Border Collie inside.