Quote:
Originally Posted by CarpeDiem51392
I'm sure this is a well hashed topic, but I've often wondered what the fuel saving "cut-off" is for shutting down vs idling in a diesel. Surely 30 secs of idle uses less fuel than shutting down and restarting? What's the upper limit though? 1min, 2, 3? I'm sure it's temperature dependent as well, a warmed up engine probably uses less fuel to restart than a cold one. How much "extra" diesel is used during the starting process if any? I realize there is probably no end all be all answer considering the multitude of diesel engines and affecting variables; I'm just wondering in an honest attempt to save fuel. Facts, testimonies,...opinions???
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What Vehicle is this question about?
I can only speak for My own Year and Model.
During Cold Weather there is no thermostatically controled Fuel Enrichment/Cold Start feature.
Glow Plugs which can be cycled for about 30 seconds of time if you ignore the Glow Plug Light before the Relay Timer turns it off; and you can repeat the Glow Plulg Cycles if you want to before starting dependant on how Good Your Battery is.
Using the Glow Plugs uses no Fuel and shortens how many times the Engine is going to Crank before it starts. Shorter Cranking time means less Fuel Used.
Using a Block Heater also costs no Diesel Fuel and aids in quick starting.
After that the Cranking time is realted to what is left in the Battery after using the Glow Plugs (during cranking the Glow Plugs are also on), the Condition of the Starter Motor, what type of Oil is in the Crankcase, how well tuned the Engine is (good Injectors, Fuel Injection Pump Timing, Valve Timing and in My case Valves adjusted), outside temp and Engine Compression.
If all of the above stuff is fixed and in good condition your wasted Fuel during cranking should be minimal.
I am not understanding other parts of the question concerning the Fuel used idling verses starting.
I can only make a guess based on what I remember from Calibrating Fuel Injection Pumps. The old Chevy Diesels used about 3.5-4 cubic centimeters of Fuel per 1000 rotations of the Fuel Injection Pump on the Test Stand.
So on the Engine that would be 3.5-4 cubic centimeters per 2000 rotations of the Engine Crankshaft.