Turbochargers operate at high temperatures. The Cool Down Timer V2.0 from BD Diesel is designed to keep the engine running when the ignition is turned off to prevent turbocharger bearing failure that could occur when the engine is shut down, stopping the cool lubricating oil flowing to the turbocharger while it is still hot. If the oil flow is shut off too early, the remaining oil in the bearing housing will overheat causing coking of the bearings which causes both premature bearing wear and reduced oiling of the bearings. Allowing the engine to idle to a minimum operating speed gives the turbocharger time to cool down. The BD Diesel Cool Down Timer Version 2.0 is adjustable for up to 5 minutes of idle time, or optionally works with any K-Type EGT probe for temperature-based shutdown.
The Cool Down Timer 2 (CDT2) is designed to keep the engine running when the ignition is turned to prevent turbocharger bearing failure that could occur when the engine is shut down and the turbocharger is still hot. The turbocharger is lubricated and cooled by the engine oil and when the engine is turned off, that oil supply is cut off. If the turbocharger is still hot at shutdown, the remaining oil in the bearing housing will overheat, causing coking of the turbocharger bearings. Over time this coking causes both premature bearing wear and reduced oiling of the bearings.
Allowing the engine to idle gives the turbocharger time to cool down before stopping the supply of lubrication oil which can prolong turbocharger life. Turbochargers rotate at high speeds, often in excess of 100,000rpm under load. If the engine is shut down too quickly after use, the residual oil in the bearing housing will not be sufficient for lubrication and may cause premature bearing wear. A short period of engine idling after use will help to ensure the turbocharger has reached a minimum operating speed before shutting down.
When the key is turned off, the CDT2 module will keep the power supplied to the ECM/PCM, which will in turn keep the engine running. On late model vehicles the CDT2 keeps most or all of the vehicle ignition system and accessories powered until engine shutdown, on early model vehicles only the engine will remain running. The CDT2 can shut the engine down once the exhaust temperature reaches a set temperature as this is the most effective method of determining a safe shut off point. The CDT2 can also be set to keep the engine on for a fixed time after the key is removed. The suggested shutdown exhaust temperature is below 400°F.