[Mxfarm]

Just throwing this out there -

But a diesel can't be ran lean. Reduce the fuel in the mixture you get less power - less power actually will give you lower temps. With diesels the it's overfueled or underfueled for the available air - overfueled = black smoke, underfueled = loss of/or less power. Let off the throttle and the injection pump reduces the fuel - air stays the same (turbos are a bit different). If you take a N/A diesel it's getting the same amount of air charge @ a idle as WOT. The only difference is the amount of fuel the injectors are spraying into the cylinder. Turbos change it a bit as the power goes up so does the amount of air being crammed into the cylinder. More air and you can inject more fuel w/o going into a overfuel state and only making black smoke. Black smoke isn't power it's only unburned fuel - but you know - probably - your not leaving any unused air in the cylinder. So your @ max power for the amount of available air.

Gas engine thinking doesn't apply to a diesel. So if your warmer than normal - I'd sure look on the coolant side first.