Ever since the PowerStroke came out, Ford has said not to allow the engine to idle for prolonged periods especially in cold temperatures or engine damage may occur. They have never defined exactly what they mean by prolonged idle or what damage may occur.
I had an opportunity to talk to a Field Service Engineer from International Engines. He told me that if the engine is allowed to idle for long periods there is the possiblity of fuel residue collecting on the exhaust valve at the stem. This usually happens when fuel quality is low. This residue may build up over a period of time to form a sludge which may harden into a resin over night in cold temperatures. This resin can prevent the valve from fully closing, which can lead to piston-valve contact. Also the resin may cause the valve to stick which will result in the push rod becoming bent.
The hydraulic lifters will pump up to reduce the clearence caused by the bent push rod and this can cause the push rod to bent more. It is possible that the rod can bend enough to become dislodged from the rocker arm or lifter, which in itself may cause damage due to the rod being loose inside the engine, and the lifter may come out of its bore which would be indicated by no indicated oil pressure on the gauge.
Due to the high compression of a diesel engine, if the exhaust valve is stuck closed this can lead to the intake push rod becoming bent and the same series of events describe for the exhaust valve above may occur. This condition where fuel residue collects on the valve stem is referred to as "wet stacking".
It seems to me that if extended idle can cause this to happen, the following may also cause wet stacking:
Starting the engine before the wait light has gone out.
Operating the engine with a non-functioning glow plug system.
Removing the thermostat or installing a lower temp thermostat.
Deactivating the Exhaust Back Pressure valve on the turbo.
To help prevent "wet stacking" from happening, use a fuel additive like Stanadyne Performance if fuel quality is in question. Allow the wait light to go out before starting and have the glow plug system checked if you suspect a problem (excessive white smoke on start-up, long crank time, crank/no start cold). If you have a turbo-mounted exhaust brake that has deleted the operation of the EBP valve, activate the brake during warm-up in cold weather. If extended idling is necessary, install an idle controller.
