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Re: 2002 duramax will heat up underload but not at idle...
No diesel I have ever owned will heat up to operating temp while idling. I have had semi's and dump truck and a Dodge with a Cummings turbo diesel. If you don't idle a diesel up to around 1200 rpm while sitting the combustion chamber temperature will drop because the diesel does not ignite fully at low rpm. You may also notice after an extended period of idling 1/2 hour or more that when you pull away the exhaust will be whitish blue because of the unburnt diesel fuel sitting on top of the rings. Also extended low idle will wash down the cylinder walls with unburnt diesel and remove the oil from lubricating the cylinders and rings. Hope this helps you understand why your diesel won't heat up while idling. Mike
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This happens when the vacuum in the manifold is at maximum and the air is drawn down past the valve stems into the combustion chamber. IT takes oil with it and so when you increase the RPM's ( moving off at lights)the burnt oil in the exhaust is expelled as a cloud of smoke . The fix here is to replace the valve stem seals that have gone hard/cracked and are no longer sealing on the valve stems
most likely a bad injector, you need to check balance rates for the injectors with a scanner. if the rates are farly equal then it is probably a rod bearing but injectors are a common problem that's why they changed the original LB7 duramax(2000-2004) from internal injectors to external so they would be easyer to change.
Check spark plugs, leads, distributor cap & rotor arm, fuel pump, fuel filter, coil pack(s), relays, replace any items that are suspect IE Fuel filter which has probably not been changed since new even though they should be changed on all vehicles every 18 months, all of this can be done at home & will save you a lot of bucks in mechanic/garage fees,